How to pretty print XML from Java

Question

I have a Java String that contains XML  with no line feeds or indentations  I would like to turn it into a String with nicely formatted XML  How do I do this   String unformattedXml     lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt    String formattedXml   new  UnknownClass    format unformattedXml     Note  My input is a String  My output is a String     Basic  mock result      lt  xml version  1 0  encoding  UTF-8   gt   lt root gt     lt tag gt       lt nested gt hello lt  nested gt     lt  tag gt   lt  root gt

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There is a very nice command line XML utility called xmlstarlet(http://xmlstar.sourceforge.net/) that can do a lot of things which a lot of people use.

You could execute this program programmatically using Runtime.exec and then read in the formatted output file. It has more options and better error reporting than a few lines of Java code can provide.

download xmlstarlet : http://sourceforge.net/project/showfiles.php?group_id=66612&package_id=64589

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I ve pretty printed in the past using the org dom4j io OutputFormat createPrettyPrint   method  public String prettyPrint final String xml          if  StringUtils isBlank xml             throw new RuntimeException  xml was null or blank in prettyPrint                 final StringWriter sw       try           final OutputFormat format   OutputFormat createPrettyPrint            final org dom4j Document document   DocumentHelper parseText xml           sw   new StringWriter            final XMLWriter writer   new XMLWriter sw  format           writer write document             catch  Exception e            throw new RuntimeException  Error pretty printing xml  n    xml  e             return sw toString

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I have found that in Java 1 6 0 32 the normal method to pretty print an XML string  using a Transformer with a null or identity xslt  does not behave as I would like if tags are merely separated by whitespace  as opposed to having no separating text  I tried using  lt xsl strip-space elements      gt  in my template to no avail  The simplest solution I found was to strip the space the way I wanted using a SAXSource and XML filter  Since my solution was for logging  I also extended this to work with incomplete XML fragments  Note the normal method seems to work fine if you use a DOMSource but I did not want to use this because of the incompleteness and memory overhead    public static class WhitespaceIgnoreFilter extends XMLFilterImpl         Override     public void ignorableWhitespace char   arg0                                      int arg1                                      int arg2  throws SAXException                 Ignore it then                Override     public void characters  char   ch                              int start                              int length  throws SAXException               if   new String ch  start  length  trim   equals                      super characters ch  start  length             public static String prettyXML String logMsg  boolean allowBadlyFormedFragments  throws SAXException  IOException  TransformerException               TransformerFactory transFactory   TransformerFactory newInstance            transFactory setAttribute  indent-number   new Integer 2            Transformer transformer   transFactory newTransformer            transformer setOutputProperty OutputKeys INDENT   yes            transformer setOutputProperty   http   xml apache org xslt indent-amount    4            StringWriter out   new StringWriter            XMLReader masterParser   SAXHelper getSAXParser true           XMLFilter parser   new WhitespaceIgnoreFilter            parser setParent masterParser            if allowBadlyFormedFragments                        transformer setErrorListener new ErrorListener                                  Override                 public void warning TransformerException exception  throws TransformerException                                                       Override                 public void fatalError TransformerException exception  throws TransformerException                                                       Override                 public void error TransformerException exception  throws TransformerException                                                                        try                       transformer transform new SAXSource parser  new InputSource new StringReader logMsg     new StreamResult out                      catch  TransformerException e                        if e getCause      null  amp  amp  e getCause   instanceof SAXParseException                                if  allowBadlyFormedFragments      XML document structures must start and end within the same entity   equals e getCause   getMessage                                           throw e                                              else                               throw e                                  out flush            return out toString

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I was trying to achieve something similar  but without any external dependency  The application was already using DOM to format just for logging the XMLs   Here is my sample snippet  public void formatXML final String unformattedXML        final int length   unformattedXML length        final int indentSpace   3      final StringBuilder newString   new StringBuilder length   length   10       final char space            int i   0      int indentCount   0      char currentChar   unformattedXML charAt i         char previousChar   currentChar      boolean nodeStarted   true      newString append currentChar       for    i  lt  length - 1             currentChar   unformattedXML charAt i             if   int  currentChar  lt  33   amp  amp   nodeStarted                continue                    switch  currentChar            case   lt                if    gt      previousChar  amp  amp         unformattedXML charAt i - 1   amp  amp         unformattedXML charAt i   amp  amp         unformattedXML charAt i                     indentCount                              newString append System lineSeparator                 for  int j   indentCount   indentSpace  j  gt  0  j--                    newString append space                             newString append currentChar               nodeStarted   true              break          case   gt                newString append currentChar               nodeStarted   false              break          case                  if    lt      previousChar      gt      unformattedXML charAt i                     indentCount--                            newString append currentChar               break          default              newString append currentChar                     previousChar   currentChar            newString append unformattedXML charAt length - 1        System out println newString toString

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Kevin Hakanson said   However  if you know your XML string is valid  and you don t want to incur the memory overhead of parsing a string into a DOM  then running a transform over the DOM to get a string back - you could just do some old fashioned character by character parsing  Insert a newline and spaces after every  characters  keep and indent counter  to determine the number of spaces  that you increment for every  lt      and decrement for every  you see    Agreed  Such an approach is much faster and has far fewer dependencies   Example solution          XML utils  including formatting      public class XmlUtils     private static XmlFormatter formatter   new XmlFormatter 2  80      public static String formatXml String s          return formatter format s  0          public static String formatXml String s  int initialIndent          return formatter format s  initialIndent          private static class XmlFormatter         private int indentNumChars      private int lineLength      private boolean singleLine       public XmlFormatter int indentNumChars  int lineLength              this indentNumChars   indentNumChars        this lineLength   lineLength             public synchronized String format String s  int initialIndent              int indent   initialIndent        StringBuilder sb   new StringBuilder          for  int i   0  i  lt  s length    i                    char currentChar   s charAt i           if  currentChar      lt                        char nextChar   s charAt i   1             if  nextChar                     indent -  indentNumChars            if   singleLine       Don t indent before closing element if we re creating opening and closing elements on a single line              sb append buildWhitespace indent              if  nextChar         amp  amp  nextChar         amp  amp  nextChar                     indent    indentNumChars            singleLine   false      Reset flag                    sb append currentChar           if  currentChar      gt                        if  s charAt i - 1                                  indent -  indentNumChars              sb append   n                          else                         int nextStartElementPos   s indexOf   lt    i               if  nextStartElementPos  gt  i   1                              String textBetweenElements   s substring i   1  nextStartElementPos                     If the space between elements is solely newlines  let them through to preserve additional newlines in source document                if  textBetweenElements replaceAll   n       length      0                                  sb append textBetweenElements     n                                     Put tags and text on a single line if the text is short                else if  textBetweenElements length    lt   lineLength   0 5                                  sb append textBetweenElements                   singleLine   true                                   For larger amounts of text  wrap lines to a maximum line length                else                                 sb append   n    lineWrap textBetweenElements  lineLength  indent  null      n                                  i   nextStartElementPos - 1                            else                             sb append   n                                                      return sb toString                 private static String buildWhitespace int numChars          StringBuilder sb   new StringBuilder        for  int i   0  i  lt  numChars  i          sb append           return sb toString                    Wraps the supplied text to the specified line length        lineLength the maximum length of each line in the returned string  not including indent if specified         indent optional number of whitespace characters to prepend to each line before the text        linePrefix optional string to append to the indent  before the text         returns the supplied text wrapped so that no line exceeds the specified line length   indent  optionally with      indent and prefix applied to each line          private static String lineWrap String s  int lineLength  Integer indent  String linePrefix          if  s    null        return null       StringBuilder sb   new StringBuilder        int lineStartPos   0      int lineEndPos      boolean firstLine   true      while lineStartPos  lt  s length                if   firstLine          sb append   n          else         firstLine   false         if  lineStartPos   lineLength  gt  s length            lineEndPos   s length   - 1        else                 lineEndPos   lineStartPos   lineLength - 1          while  lineEndPos  gt  lineStartPos  amp  amp   s charAt lineEndPos          amp  amp  s charAt lineEndPos       t              lineEndPos--                sb append buildWhitespace indent          if  linePrefix    null          sb append linePrefix          sb append s substring lineStartPos  lineEndPos   1          lineStartPos   lineEndPos   1            return sb toString              other utils removed for brevity

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Using scala   import xml   val xml   XML loadString   lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt    val formatted   new PrettyPrinter 150  2  format xml  println formatted    You can do this in Java too  if you depend on the scala-library jar  It looks like this   import scala xml     public class FormatXML       public static void main String   args            String unformattedXml     lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt            PrettyPrinter pp   new PrettyPrinter 150  3           String formatted   pp format XML loadString unformattedXml   TopScope  MODULE            System out println formatted             The PrettyPrinter object is constructed with two ints  the first being max line length and the second being the indentation step

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Here s an answer to my own question  I combined the answers from the various results to write a class that pretty prints XML   No guarantees on how it responds with invalid XML or large documents   package ecb sdw pretty   import org apache xml serialize OutputFormat  import org apache xml serialize XMLSerializer  import org w3c dom Document  import org xml sax InputSource  import org xml sax SAXException   import javax xml parsers DocumentBuilder  import javax xml parsers DocumentBuilderFactory  import javax xml parsers ParserConfigurationException  import java io IOException  import java io StringReader  import java io StringWriter  import java io Writer          Pretty-prints xml  supplied as a string      lt p  gt     eg      lt code gt     String formattedXml   new XmlFormatter   format   lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt         lt  code gt      public class XmlFormatter        public XmlFormatter                public String format String unformattedXml            try               final Document document   parseXmlFile unformattedXml                OutputFormat format   new OutputFormat document               format setLineWidth 65               format setIndenting true               format setIndent 2               Writer out   new StringWriter                XMLSerializer serializer   new XMLSerializer out  format               serializer serialize document                return out toString              catch  IOException e                throw new RuntimeException e                        private Document parseXmlFile String in            try               DocumentBuilderFactory dbf   DocumentBuilderFactory newInstance                DocumentBuilder db   dbf newDocumentBuilder                InputSource is   new InputSource new StringReader in                return db parse is             catch  ParserConfigurationException e                throw new RuntimeException e             catch  SAXException e                throw new RuntimeException e             catch  IOException e                throw new RuntimeException e                        public static void main String   args            String unformattedXml                     lt  xml version   1 0   encoding   UTF-8    gt  lt QueryMessage n                                     xmlns   http   www SDMX org resources SDMXML schemas v2 0 message   n                                     xmlns query   http   www SDMX org resources SDMXML schemas v2 0 query   gt  n                                  lt Query gt  n                                      lt query CategorySchemeWhere gt  n                                 t t t t t          lt query AgencyID gt ECB n n n n lt  query AgencyID gt  n                                      lt  query CategorySchemeWhere gt  n                                  lt  Query gt  n n n n n                              lt  QueryMessage gt             System out println new XmlFormatter   format unformattedXml

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Since you are starting with a String  you need to covert to a DOM object  e g  Node  before you can use the Transformer    However  if you know your XML string is valid  and you don t want to incur the memory overhead of parsing a string into a DOM  then running a transform over the DOM to get a string back - you could just do some old fashioned character by character parsing   Insert a newline and spaces after every  lt      gt  characters  keep and indent counter  to determine the number of spaces  that you increment for every  lt     gt  and decrement for every  lt      gt  you see   Disclaimer - I did a cut paste text edit of the functions below  so they may not compile as is   public static final Element createDOM String strXML       throws ParserConfigurationException  SAXException  IOException        DocumentBuilderFactory dbf   DocumentBuilderFactory newInstance        dbf setValidating true       DocumentBuilder db   dbf newDocumentBuilder        InputSource sourceXML   new InputSource new StringReader strXML        Document xmlDoc   db parse sourceXML       Element e   xmlDoc getDocumentElement        e normalize        return e     public static final void prettyPrint Node xml  OutputStream out      throws TransformerConfigurationException  TransformerFactoryConfigurationError  TransformerException       Transformer tf   TransformerFactory newInstance   newTransformer        tf setOutputProperty OutputKeys OMIT XML DECLARATION   yes        tf setOutputProperty OutputKeys ENCODING   UTF-8        tf setOutputProperty OutputKeys INDENT   yes        tf transform new DOMSource xml   new StreamResult out

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I always use the below function   public static String prettyPrintXml String xmlStringToBeFormatted        String formattedXmlString   null      try           DocumentBuilderFactory documentBuilderFactory   DocumentBuilderFactory newInstance            documentBuilderFactory setValidating true           DocumentBuilder documentBuilder   documentBuilderFactory newDocumentBuilder            InputSource inputSource   new InputSource new StringReader xmlStringToBeFormatted            Document document   documentBuilder parse inputSource            Transformer transformer   TransformerFactory newInstance   newTransformer            transformer setOutputProperty OutputKeys INDENT   yes            transformer setOutputProperty   http   xml apache org xslt indent-amount    2             StreamResult streamResult   new StreamResult new StringWriter             DOMSource dOMSource   new DOMSource document           transformer transform dOMSource  streamResult           formattedXmlString   streamResult getWriter   toString   trim          catch  Exception ex            StringWriter sw   new StringWriter            ex printStackTrace new PrintWriter sw            System err println sw toString               return formattedXmlString

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Underscore-java has static method U formatXml string   I am the maintainer of the project  Live example  import com github underscore lodash U   public class MyClass       public static void main String args              String xml     lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt             System out println U formatXml   lt  xml version   1 0   encoding   UTF-8    gt  lt root gt     xml     lt  root gt                Output    lt  xml version  1 0  encoding  UTF-8   gt   lt root gt      lt tag gt         lt nested gt hello lt  nested gt      lt  tag gt   lt  root gt

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I should have looked for this page first before coming up with my own solution   Anyway  mine uses Java recursion to parse the xml page   This code is totally self-contained and does not rely on third party libraries   Also    it uses recursion      you call this method passing in the xml text public static void prettyPrint String text       prettyPrint text  0          index  corresponds to the number of levels of nesting and or the number of tabs to print before printing the tag public static void prettyPrint String xmlText  int index       boolean foundTagStart   false      StringBuilder tagChars   new StringBuilder        String startTag           String endTag           String   chars   xmlText split             find the next start tag     for String ch   chars           if ch equalsIgnoreCase   lt                  tagChars append ch               foundTagStart   true            else if ch equalsIgnoreCase   gt     amp  amp  foundTagStart               startTag   tagChars append ch  toString                String tempTag   startTag              endTag    tempTag contains          tempTag split      0      gt      tempTag  replace   lt      lt          lt startTag attr1 1 attr2 2 gt    gt   lt  startTag gt              break            else if foundTagStart               tagChars append ch                          once start and end tag are calculated  print start tag  then content  then end tag     if foundTagStart           int startIndex   xmlText indexOf startTag           int endIndex   xmlText indexOf endTag              handle if matching tags NOT found         if  startIndex  lt  0      endIndex  lt  0                if startIndex  lt  0                       no start tag found                 return                else                      start tag found  no end tag found  handles single tags aka   lt mytag  gt   or   lt  xml     gt                    printTabs index                   System out println startTag                      move on to the next tag                    NOTE   index   not index 1  because next tag is on same level as this one                 prettyPrint xmlText substring startIndex startTag length    xmlText length     index                   return                           handle when matching tags found           else               String content   xmlText substring startIndex startTag length    endIndex               boolean isTagContainsTags   content contains   lt        content contains tags             printTabs index               if isTagContainsTags      ie   lt tag1 gt  lt tag2 gt stuff lt  tag2 gt  lt  tag1 gt                  System out println startTag                   prettyPrint content  index 1       index 1  because  content  is nested                 printTabs index                 else                   System out print startTag      ie   lt tag1 gt stuff lt  tag1 gt  or  lt tag1 gt  lt  tag1 gt                  System out print content                             System out println endTag               int nextIndex   endIndex   endTag length                if xmlText length    gt  nextIndex      if there are more tags on this level  continue                 prettyPrint xmlText substring nextIndex  xmlText length     index                                 else           System out print xmlText            private static void printTabs int counter       while counter--  gt  0            System out print   t

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Try this    try                                               TransformerFactory transFactory   TransformerFactory newInstance                            Transformer transformer   null                          transformer   transFactory newTransformer                            StringWriter buffer   new StringWriter                            transformer setOutputProperty OutputKeys OMIT XML DECLARATION   yes                            transformer transform new DOMSource element                                     new StreamResult buffer                             String str   buffer toString                            System out println  XML INSIDE IS                                            str                           return element                                            catch  TransformerConfigurationException e                                                e printStackTrace                                              catch  TransformerException e                                                e printStackTrace

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Here s a way of doing it using dom4j   Imports   import org dom4j Document    import org dom4j DocumentHelper    import org dom4j io OutputFormat    import org dom4j io XMLWriter    Code    String xml     lt your xml  here   gt      Document doc   DocumentHelper parseText xml     StringWriter sw   new StringWriter      OutputFormat format   OutputFormat createPrettyPrint      XMLWriter xw   new XMLWriter sw  format     xw write doc     String result   sw toString

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For those searching for a quick and dirty solution - which doesn t need the XML to be 100  valid  e g  in case of REST   SOAP logging  you never know what the others send  -    I found and advanced a code snipped I found online which I think is still missing here as a valid possible approach    public static String prettyPrintXMLAsString String xmlString           Remove new lines        final String LINE BREAK     n       xmlString   xmlString replaceAll LINE BREAK           StringBuffer prettyPrintXml   new StringBuffer           Group the xml tags        Pattern pattern   Pattern compile    lt        gt    gt       lt      lt     gt    gt     lt        gt     gt           Matcher matcher   pattern matcher xmlString       int tabCount   0      while  matcher find              String str1    null    matcher group 1      null  equals matcher group            matcher group 1           String str2    null    matcher group 2      null  equals matcher group            matcher group 2           String str3    null    matcher group 3      null  equals matcher group            matcher group 3           String str4    null    matcher group 4      null  equals matcher group            matcher group 4            if  matcher group      null  amp  amp   matcher group   trim   equals                    printTabs tabCount  prettyPrintXml               if   str1 equals      amp  amp  str3 equals                          tabCount                            if  str1 equals      amp  amp   str3 equals                        --tabCount                  prettyPrintXml deleteCharAt prettyPrintXml length   - 1                              prettyPrintXml append str1               prettyPrintXml append str2               prettyPrintXml append str3               if   str4 equals                        prettyPrintXml append LINE BREAK                   printTabs tabCount  prettyPrintXml                   prettyPrintXml append str4                             prettyPrintXml append LINE BREAK                       return prettyPrintXml toString       private static void printTabs int count  StringBuffer stringBuffer        for  int i   0  i  lt  count  i              stringBuffer append   t             public static void main String   args        String x   new String                lt soap Envelope xmlns soap   http   schemas xmlsoap org soap envelope    gt  lt soap Body gt  lt soap Fault gt  lt faultcode gt soap Client lt  faultcode gt  lt faultstring gt INVALID MESSAGE lt  faultstring gt  lt detail gt  lt ns3 XcbSoapFault xmlns      xmlns ns3   http   www someapp eu xcb types xcb v1   gt  lt CauseCode gt 20007 lt  CauseCode gt  lt CauseText gt INVALID MESSAGE lt  CauseText gt  lt DebugInfo gt Problems creating SAAJ object model lt  DebugInfo gt  lt  ns3 XcbSoapFault gt  lt  detail gt  lt  soap Fault gt  lt  soap Body gt  lt  soap Envelope gt         System out println prettyPrintXMLAsString x        here is the output    lt soap Envelope xmlns soap  http   schemas xmlsoap org soap envelope   gt     lt soap Body gt       lt soap Fault gt           lt faultcode gt soap Client lt  faultcode gt           lt faultstring gt INVALID MESSAGE lt  faultstring gt           lt detail gt               lt ns3 XcbSoapFault xmlns    xmlns ns3  http   www someapp eu xcb types xcb v1  gt                   lt CauseCode gt 20007 lt  CauseCode gt                   lt CauseText gt INVALID MESSAGE lt  CauseText gt                   lt DebugInfo gt Problems creating SAAJ object model lt  DebugInfo gt               lt  ns3 XcbSoapFault gt           lt  detail gt       lt  soap Fault gt     lt  soap Body gt   lt  soap Envelope gt

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The solutions I have found here for Java 1 6  do not reformat the code if it is already formatted  The one that worked for me  and re-formatted already formatted code  was the following   import org apache xml security c14n CanonicalizationException  import org apache xml security c14n Canonicalizer  import org apache xml security c14n InvalidCanonicalizerException  import org w3c dom Element  import org w3c dom bootstrap DOMImplementationRegistry  import org w3c dom ls DOMImplementationLS  import org w3c dom ls LSSerializer  import org xml sax InputSource  import org xml sax SAXException   import javax xml parsers DocumentBuilderFactory  import javax xml parsers ParserConfigurationException  import javax xml transform TransformerException  import java io IOException  import java io StringReader   public class XmlUtils       public static String toCanonicalXml String xml  throws InvalidCanonicalizerException  ParserConfigurationException  SAXException  CanonicalizationException  IOException           Canonicalizer canon   Canonicalizer getInstance Canonicalizer ALGO ID C14N OMIT COMMENTS           byte canonXmlBytes     canon canonicalize xml getBytes             return new String canonXmlBytes              public static String prettyFormat String input  throws TransformerException  ParserConfigurationException  IOException  SAXException  InstantiationException  IllegalAccessException  ClassNotFoundException           InputSource src   new InputSource new StringReader input            Element document   DocumentBuilderFactory newInstance   newDocumentBuilder   parse src  getDocumentElement            Boolean keepDeclaration   input startsWith   lt  xml            DOMImplementationRegistry registry   DOMImplementationRegistry newInstance            DOMImplementationLS impl    DOMImplementationLS  registry getDOMImplementation  LS            LSSerializer writer   impl createLSSerializer            writer getDomConfig   setParameter  format-pretty-print   Boolean TRUE           writer getDomConfig   setParameter  xml-declaration   keepDeclaration           return writer writeToString document             It is a good tool to use in your unit tests for full-string xml comparison    private void assertXMLEqual String expected  String actual  throws ParserConfigurationException  IOException  SAXException  CanonicalizationException  InvalidCanonicalizerException  TransformerException  IllegalAccessException  ClassNotFoundException  InstantiationException       String canonicalExpected   prettyFormat toCanonicalXml expected        String canonicalActual   prettyFormat toCanonicalXml actual        assertEquals canonicalExpected  canonicalActual

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As an alternative to the answers from max  codeskraps  David Easley and milosmns  have a look at my lightweight  high-performance pretty-printer library  xml-formatter     construct lightweight  threadsafe  instance PrettyPrinter prettyPrinter   PrettyPrinterBuilder newPrettyPrinter   build     StringBuilder buffer   new StringBuilder    String xml          also works with char   or Reader  if prettyPrinter process xml  buffer             valid XML  print buffer   else           invalid XML  print xml     Sometimes  like when running mocked SOAP services directly from file  it is good to have a pretty-printer which also handles already pretty-printed XML   PrettyPrinter prettyPrinter   PrettyPrinterBuilder newPrettyPrinter   ignoreWhitespace   build      As some have commented  pretty-printing is just a way of presenting XML in a more human-readable form - whitespace strictly does not belong in your XML data    The library is intended for pretty-printing for logging purposes  and also includes functions for filtering  subtree removal   anonymization  and pretty-printing of XML in CDATA and Text nodes

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Regarding comment that  you must first build a DOM tree   No  you need not and should not do that   Instead  create a StreamSource  new StreamSource new StringReader str    and feed that to the identity transformer mentioned  That ll use SAX parser  and result will be much faster  Building an intermediate tree is pure overhead for this case  Otherwise the top-ranked answer is good

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I saw one answer using Scala  so here is another one in Groovy  just in case someone finds it interesting  The default indentation is 2 steps  XmlNodePrinter constructor can be passed another value as well   def xml     lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt   def stringWriter   new StringWriter   def node   new XmlParser   parseText xml   new XmlNodePrinter new PrintWriter stringWriter   print node  println stringWriter toString     Usage from Java if groovy jar is in classpath    String xml     lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt      StringWriter stringWriter   new StringWriter      Node node   new XmlParser   parseText xml     new XmlNodePrinter new PrintWriter stringWriter   print node     System out println stringWriter toString

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slightly improved version from milosmns     public static String getPrettyXml String xml        if  xml    null    xml trim   length      0  return          int stack   0      StringBuilder pretty   new StringBuilder        String   rows   xml trim   replaceAll   gt      gt  n   replaceAll   lt      n lt    split   n         for  int i   0  i  lt  rows length  i              if  rows i     null    rows i  trim   length      0  continue           String row   rows i  trim            if  row startsWith   lt                    pretty append row     n              else if  row startsWith   lt                    String indent   repeatString --stack               pretty append indent   row     n              else if  row startsWith   lt     amp  amp  row endsWith    gt       false                String indent   repeatString stack                 pretty append indent   row     n                if  row endsWith     gt     stack--            else               String indent   repeatString stack               pretty append indent   row     n                         return pretty toString   trim       private static String repeatString int stack         StringBuilder indent   new StringBuilder         for  int i   0  i  lt  stack  i              indent append                   return indent toString

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a simpler solution based on this answer    public static String prettyFormat String input  int indent        try           Source xmlInput   new StreamSource new StringReader input            StringWriter stringWriter   new StringWriter            StreamResult xmlOutput   new StreamResult stringWriter           TransformerFactory transformerFactory   TransformerFactory newInstance            transformerFactory setAttribute  indent-number   indent           Transformer transformer   transformerFactory newTransformer             transformer setOutputProperty OutputKeys INDENT   yes            transformer transform xmlInput  xmlOutput           return xmlOutput getWriter   toString          catch  Exception e            throw new RuntimeException e      simple exception handling  please review it          public static String prettyFormat String input        return prettyFormat input  2       testcase   prettyFormat   lt root gt  lt child gt aaa lt  child gt  lt child  gt  lt  root gt       returns    lt  xml version  1 0  encoding  UTF-8   gt   lt root gt     lt child gt aaa lt  child gt     lt child  gt   lt  root gt

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Just for future reference  here s a solution that worked for me  thanks to a comment that  George Hawkins posted in one of the answers    DOMImplementationRegistry registry   DOMImplementationRegistry newInstance    DOMImplementationLS impl    DOMImplementationLS  registry getDOMImplementation  LS    LSSerializer writer   impl createLSSerializer    writer getDomConfig   setParameter  format-pretty-print   Boolean TRUE   LSOutput output   impl createLSOutput    ByteArrayOutputStream out   new ByteArrayOutputStream    output setByteStream out   writer write document  output   String xmlStr   new String out toByteArray

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If you re sure that you have a valid XML  this one is simple  and avoids XML DOM trees  Maybe has some bugs  do comment if you see anything  public String prettyPrint String xml                if  xml    null    xml trim   length      0  return                  int stack   0              StringBuilder pretty   new StringBuilder                String   rows   xml trim   replaceAll   gt      gt  n   replaceAll   lt      n lt    split   n                 for  int i   0  i  lt  rows length  i                          if  rows i     null    rows i  trim   length      0  continue                       String row   rows i  trim                        if  row startsWith   lt                                       xml version tag                             pretty append row     n                          else if  row startsWith   lt                                       closing tag                             String indent   repeatString         --stack                               pretty append indent   row     n                          else if  row startsWith   lt                                      starting tag                             String indent   repeatString         stack                                 pretty append indent   row     n                          else                                  tag data                             String indent   repeatString         stack                               pretty append indent   row     n                                                     return pretty toString   trim

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Hmmm    faced something like this and it is a known bug      just add this OutputProperty     transformer setOutputProperty OutputPropertiesFactory S KEY INDENT AMOUNT   8      Hope this helps

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In case you do not need indentation that much but a few line breaks  it could be sufficient to simply regex     String leastPrettifiedXml   uglyXml replaceAll   gt  lt      gt  n lt       The code is nice  not the result because of missing indentation       For solutions with indentation  see other answers

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Just to note that top rated answer requires the use of xerces   If you don t want to add this external dependency then you can simply use the standard jdk libraries  which actually are built using xerces internally    N B  There was a bug with jdk version 1 5 see http   bugs sun com bugdatabase view bug do bug id 6296446 but it is resolved now     Note if an error occurs this will return the original text   package com test   import java io ByteArrayInputStream  import java io ByteArrayOutputStream   import javax xml transform OutputKeys  import javax xml transform Source  import javax xml transform Transformer  import javax xml transform sax SAXSource  import javax xml transform sax SAXTransformerFactory  import javax xml transform stream StreamResult   import org xml sax InputSource   public class XmlTest       public static void main String   args            XmlTest t   new XmlTest            System out println t formatXml   lt a gt  lt b gt  lt c  gt  lt d gt text D lt  d gt  lt e value  0   gt  lt  b gt  lt  a gt                 public String formatXml String xml           try              Transformer serializer  SAXTransformerFactory newInstance   newTransformer                serializer setOutputProperty OutputKeys INDENT   yes                  serializer setOutputProperty OutputKeys OMIT XML DECLARATION   yes                serializer setOutputProperty   http   xml apache org xslt indent-amount    2                  serializer setOutputProperty   http   xml customer org xslt indent-amount    2                Source xmlSource new SAXSource new InputSource new ByteArrayInputStream xml getBytes                   StreamResult res    new StreamResult new ByteArrayOutputStream                             serializer transform xmlSource  res               return new String   ByteArrayOutputStream res getOutputStream    toByteArray              catch Exception e                 TODO log error             return xml

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I had the same problem and I m having great success with JTidy  http   jtidy sourceforge net index html   Example   Tidy t   new Tidy    t setIndentContent true   Document d   t parseDOM      new ByteArrayInputStream  HTML goes here   null    OutputStream out   new ByteArrayOutputStream    t pprint d  out   String html   out toString

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Just another solution which works for us  import java io StringWriter  import org dom4j DocumentHelper  import org dom4j io OutputFormat  import org dom4j io XMLWriter         Pretty Print XML String         param inputXmlString     return     public static String prettyPrintXml String xml         final StringWriter sw       try           final OutputFormat format   OutputFormat createPrettyPrint            final org dom4j Document document   DocumentHelper parseText xml           sw   new StringWriter            final XMLWriter writer   new XMLWriter sw  format           writer write document             catch  Exception e            throw new RuntimeException  Error pretty printing xml  n    xml  e             return sw toString

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I mix all of them and writing one small program  It is reading from the xml file and printing out  Just Instead of xzy give your file path       public static void main String   args  throws Exception       DocumentBuilderFactory dbf   DocumentBuilderFactory newInstance        dbf setValidating false       DocumentBuilder db   dbf newDocumentBuilder        Document doc   db parse new FileInputStream new File  C  Users xyz xml          prettyPrint doc       private static String prettyPrint Document document          throws TransformerException       TransformerFactory transformerFactory   TransformerFactory              newInstance        Transformer transformer   transformerFactory newTransformer        transformer setOutputProperty OutputKeys INDENT   yes        transformer setOutputProperty   http   xml apache org xslt indent-amount    2        transformer setOutputProperty OutputKeys ENCODING   UTF-8        transformer setOutputProperty OutputKeys OMIT XML DECLARATION   no        DOMSource source   new DOMSource document       StringWriter strWriter   new StringWriter        StreamResult result   new StreamResult strWriter  transformer transform source  result       System out println strWriter getBuffer   toString          return strWriter getBuffer   toString

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Transformer transformer   TransformerFactory newInstance   newTransformer    transformer setOutputProperty OutputKeys INDENT   yes    transformer setOutputProperty   http   xml apache org xslt indent-amount    2      initialize StreamResult with File object to save to file StreamResult result   new StreamResult new StringWriter     DOMSource source   new DOMSource doc   transformer transform source  result   String xmlString   result getWriter   toString    System out println xmlString     Note  Results may vary depending on the Java version  Search for workarounds specific to your platform

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I ve pretty printed in the past using the org dom4j io OutputFormat createPrettyPrint   method  public String prettyPrint final String xml          if  StringUtils isBlank xml             throw new RuntimeException  xml was null or blank in prettyPrint                 final StringWriter sw       try           final OutputFormat format   OutputFormat createPrettyPrint            final org dom4j Document document   DocumentHelper parseText xml           sw   new StringWriter            final XMLWriter writer   new XMLWriter sw  format           writer write document             catch  Exception e            throw new RuntimeException  Error pretty printing xml  n    xml  e             return sw toString

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This code below working perfectly  import javax xml transform OutputKeys  import javax xml transform Source  import javax xml transform Transformer  import javax xml transform TransformerFactory  import javax xml transform stream StreamResult  import javax xml transform stream StreamSource   String formattedXml1   prettyFormat   lt root gt  lt child gt aaa lt  child gt  lt child  gt  lt  root gt      public static String prettyFormat String input        return prettyFormat input   2       public static String prettyFormat String input  String indent        Source xmlInput   new StreamSource new StringReader input        StringWriter stringWriter   new StringWriter        try           TransformerFactory transformerFactory   TransformerFactory newInstance            Transformer transformer   transformerFactory newTransformer            transformer setOutputProperty OutputKeys INDENT   yes            transformer setOutputProperty   http   xml apache org xslt indent-amount   indent           transformer transform xmlInput  new StreamResult stringWriter             String pretty   stringWriter toString            pretty   pretty replace   r n     n            return pretty                      catch  Exception e            throw new RuntimeException e

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Now it s 2012 and Java can do more than it used to with XML  I d like to add an alternative to my accepted answer  This has no dependencies outside of Java 6   import org w3c dom Node  import org w3c dom bootstrap DOMImplementationRegistry  import org w3c dom ls DOMImplementationLS  import org w3c dom ls LSSerializer  import org xml sax InputSource   import javax xml parsers DocumentBuilderFactory  import java io StringReader          Pretty-prints xml  supplied as a string      lt p  gt     eg      lt code gt     String formattedXml   new XmlFormatter   format   lt tag gt  lt nested gt hello lt  nested gt  lt  tag gt         lt  code gt      public class XmlFormatter        public String format String xml             try               final InputSource src   new InputSource new StringReader xml                final Node document   DocumentBuilderFactory newInstance   newDocumentBuilder   parse src  getDocumentElement                final Boolean keepDeclaration   Boolean valueOf xml startsWith   lt  xml                May need this  System setProperty DOMImplementationRegistry PROPERTY  com sun org apache xerces internal dom DOMImplementationSourceImpl                  final DOMImplementationRegistry registry   DOMImplementationRegistry newInstance                final DOMImplementationLS impl    DOMImplementationLS  registry getDOMImplementation  LS                final LSSerializer writer   impl createLSSerializer                 writer getDomConfig   setParameter  format-pretty-print   Boolean TRUE      Set this to true if the output needs to be beautified              writer getDomConfig   setParameter  xml-declaration   keepDeclaration      Set this to true if the declaration is needed to be outputted               return writer writeToString document             catch  Exception e                throw new RuntimeException e                        public static void main String   args            String unformattedXml                     lt  xml version   1 0   encoding   UTF-8    gt  lt QueryMessage n                                     xmlns   http   www SDMX org resources SDMXML schemas v2 0 message   n                                     xmlns query   http   www SDMX org resources SDMXML schemas v2 0 query   gt  n                                  lt Query gt  n                                      lt query CategorySchemeWhere gt  n                                 t t t t t          lt query AgencyID gt ECB n n n n lt  query AgencyID gt  n                                      lt  query CategorySchemeWhere gt  n                                  lt  Query gt  n n n n n                              lt  QueryMessage gt             System out println new XmlFormatter   format unformattedXml

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If using a 3rd party XML library is ok  you can get away with something significantly simpler than what the currently highest-voted answers suggest     It was stated that both input and output should be Strings  so here s a utility method that does just that  implemented with the XOM library   import nu xom    import java io            public static String format String xml  throws ParsingException  IOException       ByteArrayOutputStream out   new ByteArrayOutputStream        Serializer serializer   new Serializer out       serializer setIndent 4       or whatever you like     serializer write new Builder   build xml            return out toString  UTF-8        I tested that it works  and the results do not depend on your JRE version or anything like that  To see how to customise the output format to your liking  take a look at the Serializer API   This actually came out longer than I thought - some extra lines were needed because Serializer wants an OutputStream to write to  But note that there s very little code for actual XML twiddling here    This answer is part of my evaluation of XOM  which was suggested as one option in my question about the best Java XML library to replace dom4j  For the record  with dom4j you could achieve this with similar ease using XMLWriter and OutputFormat  Edit     as demonstrated in mlo55 s answer

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Using jdom2   http   www jdom org   import java io StringReader  import org jdom2 input SAXBuilder  import org jdom2 output Format  import org jdom2 output XMLOutputter   String prettyXml   new XMLOutputter Format getPrettyFormat                              outputString new SAXBuilder   build new StringReader uglyXml

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All above solutions didn t work for me  then I found this http   myshittycode com 2014 02 10 java-properly-indenting-xml-string   The clue is remove whitespaces with XPath      String xml     lt root gt                    n                      n lt name gt Coco Puff lt  name gt                    n         lt total gt 10 lt  total gt      lt  root gt     try       Document document   DocumentBuilderFactory newInstance                newDocumentBuilder                parse new InputSource new ByteArrayInputStream xml getBytes  utf-8            XPath xPath   XPathFactory newInstance   newXPath        NodeList nodeList    NodeList  xPath evaluate    text   normalize-space                                                           document                                                    XPathConstants NODESET        for  int i   0  i  lt  nodeList getLength      i            Node node   nodeList item i           node getParentNode   removeChild node              Transformer transformer   TransformerFactory newInstance   newTransformer        transformer setOutputProperty OutputKeys ENCODING   UTF-8        transformer setOutputProperty OutputKeys OMIT XML DECLARATION   yes        transformer setOutputProperty OutputKeys INDENT   yes        transformer setOutputProperty   http   xml apache org xslt indent-amount    4         StringWriter stringWriter   new StringWriter        StreamResult streamResult   new StreamResult stringWriter        transformer transform new DOMSource document   streamResult        System out println stringWriter toString       catch  Exception e        e printStackTrace

[java] How to pretty print XML from Java?

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