How to replace a set of tokens in a Java String

Question

I have the following template String   Hello  Name  Please find attached  Invoice Number  which is due on  Due Date     I also have String variables for name  invoice number and due date - what s the best way to replace the tokens in the template with the variables      Note that if a variable happens to contain a token it should NOT be replaced      EDIT  With thanks to  laginimaineb and  alan-moore  here s my solution   public static String replaceTokens String text                                      Map lt String  String gt  replacements        Pattern pattern   Pattern compile                     Matcher matcher   pattern matcher text       StringBuffer buffer   new StringBuffer         while  matcher find              String replacement   replacements get matcher group 1            if  replacement    null                   matcher appendReplacement buffer  replacement                  see comment              matcher appendReplacement buffer                   buffer append replacement                       matcher appendTail buffer       return buffer toString

User · Accepted Answer

The most efficient way would be using a matcher to continually find the expressions and replace them  then append the text to a string builder   Pattern pattern   Pattern compile                 Matcher matcher   pattern matcher text   HashMap lt String String gt  replacements   new HashMap lt String String gt       populate the replacements map     StringBuilder builder   new StringBuilder    int i   0  while  matcher find          String replacement   replacements get matcher group 1        builder append text substring i  matcher start          if  replacement    null          builder append matcher group 0        else         builder append replacement       i   matcher end      builder append text substring i  text length      return builder toString

User · Answer

In the past  I ve solved this kind of problem with StringTemplate and Groovy Templates     Ultimately  the decision of using a templating engine or not should be based on the following factors    Will you have many of these templates in the application  Do you need the ability to modify the templates without restarting the application  Who will be maintaining these templates   A Java programmer or a business analyst involved on the project  Will you need to the ability to put logic in your templates  like conditional text based on values in the variables   Will you need the ability to include other templates in a template    If any of the above applies to your project  I would consider using a templating engine  most of which provide this functionality  and more

User · Answer

I really don t think you need to use a templating engine or anything like that for this   You can use the String format method  like so   String template    Hello  s Please find attached  s which is due on  s    String message   String format template  name  invoiceNumber  dueDate

User · Answer

My solution for replacing   variable  style tokens  inspired by the answers here and by the Spring UriTemplate    public static String substituteVariables String template  Map lt String  String gt  variables        Pattern pattern   Pattern compile                        Matcher matcher   pattern matcher template          StringBuilder cannot be used here because Matcher expects StringBuffer     StringBuffer buffer   new StringBuffer        while  matcher find              if  variables containsKey matcher group 1                  String replacement   variables get matcher group 1                   quote to work properly with   and     signs             matcher appendReplacement buffer  replacement    null   Matcher quoteReplacement replacement     null                        matcher appendTail buffer       return buffer toString

User · Answer

String format  Hello  s Please find attached  s which is due on  s   name  invoice  date

User · Answer

With Apache Commons Library  you can simply use Stringutils replaceEach   public static String replaceEach String text                               String   searchList                               String   replacementList    From the documentation      Replaces all occurrences of Strings within another String       A null reference passed to this method is a no-op  or if any  search   string  or  string to replace  is null  that replace will be ignored    This will not repeat  For repeating replaces  call the overloaded   method     StringUtils replaceEach null                 null    StringUtils replaceEach                            StringUtils replaceEach  aba   null  null     aba     StringUtils replaceEach  aba   new String 0   null     aba     StringUtils replaceEach  aba   null  new String 0      aba     StringUtils replaceEach  aba   new String    a    null      aba     StringUtils replaceEach  aba   new String    a    new String            b     StringUtils replaceEach  aba   new String   null   new String    a        aba     StringUtils replaceEach  abcde   new String    ab    d    new String    w    t        wcte     example of how it does not repeat   StringUtils replaceEach  abcde   new String    ab    d    new String    d    t        dcte

User · Answer

It depends of where the actual data that you want to replace is located   You might have a Map like this   Map lt String  String gt  values   new HashMap lt String  String gt       containing all the data that can be replaced   Then you can iterate over the map and change everything in the String as follows   String s    Your String with  Fields    for  Map Entry lt String  String gt  e   values entrySet        s   s replaceAll         e getKey            e getValue         You could also iterate over the String and find the elements in the map   But that is a little  bit more complicated because you need to parse the String searching for the      You could do it with a regular expression using Pattern and Matcher

User · Answer

You could try using a templating library like Apache Velocity   http   velocity apache org   Here is an example   import org apache velocity VelocityContext  import org apache velocity app Velocity   import java io StringWriter   public class TemplateExample       public static void main String args    throws Exception           Velocity init             VelocityContext context   new VelocityContext            context put  name    Mark            context put  invoiceNumber    42123            context put  dueDate    June 6  2009             String template    Hello  name  Please find attached invoice                                 invoiceNumber which is due on  dueDate            StringWriter writer   new StringWriter            Velocity evaluate context  writer   TemplateName   template            System out println writer             The output would be   Hello Mark  Please find attached invoice 42123 which is due on June 6  2009

User · Answer

http   github com niesfisch tokenreplacer

User · Answer

System out println MessageFormat format  Hello  0   You have  1  messages    Join  10L      Output  Hello Join  You have 10 messages

User · Answer

You can use template library for complex template replacement   FreeMarker is a very good choice   http   freemarker sourceforge net   But for simple task  there is a simple utility class can help you   org apache commons lang3 text StrSubstitutor  It is very powerful  customizable  and easy to use      This class takes a piece of text and substitutes all the variables   within it  The default definition of a variable is   variableName     The prefix and suffix can be changed via constructors and set methods       Variable values are typically resolved from a map  but could also be   resolved from system properties  or by supplying a custom variable   resolver    For example  if you want to substitute system environment variable into a template string  here is the code   public class SysEnvSubstitutor       public static final String replace final String source            StrSubstitutor strSubstitutor   new StrSubstitutor                  new StrLookup lt Object gt                           Override                     public String lookup final String key                            return System getenv key                                                     return strSubstitutor replace source

User · Answer

Unfortunately the comfortable method String format mentioned above is only available starting with Java 1 5  which should be pretty standard nowadays  but you never know   Instead of that you might also use Java s class MessageFormat for replacing the placeholders   It supports placeholders in the form   number    so your message would look like  Hello  0  Please find attached  1  which is due on  2    These Strings can easily be externalized using ResourceBundles  e  g  for localization with multiple locales   The replacing would be done using the static format  method of class MessageFormat   String msg    Hello  0  Please find attached  1  which is due on  2    String   values        John Doe    invoice  123    2009-06-30     System out println MessageFormat format msg  values

User · Answer

The following replaces variables of the form  lt  lt VAR gt  gt   with values looked up from a Map  You can test it online here  For example  with the following input string  BMI   lt  lt Weight gt  gt    lt  lt Height gt  gt   lt  lt Height gt  gt      70 Hi there  lt  lt Weight gt  gt  was here   and the following variable values  Weight  42 Height  HEIGHT 51   outputs the following  BMI  42  HEIGHT 51 HEIGHT 51     70  Hi there 42 was here   Here s the code    static Pattern pattern   Pattern compile   lt  lt   a-z  a-z0-9    gt  gt    Pattern CASE INSENSITIVE      public static String replaceVarsWithValues String message  Map lt String String gt  varValues        try         StringBuffer newStr   new StringBuffer message         int lenDiff   0        Matcher m   pattern matcher message         while  m find              String fullText   m group 0           String keyName   m group 1           String newValue   varValues get keyName              String replacementText   newValue          newStr   newStr replace m start   - lenDiff  m end   - lenDiff  replacementText           lenDiff    fullText length   - replacementText length                  return newStr toString          catch  Exception e          return message                public static void main String args    throws Exception         String testString    BMI   lt  lt Weight gt  gt    lt  lt Height gt  gt   lt  lt Height gt  gt      70 n nHi there  lt  lt Weight gt  gt  was here         HashMap lt String String gt  values   new HashMap lt  gt           values put  Weight    42          values put  Height    HEIGHT 51          System out println replaceVarsWithValues testString  values          and although not requested  you can use a similar approach to replace variables in a string with properties from your application properties file  though this may already be being done   private static Pattern patternMatchForProperties         Pattern compile           a-z0-9          Pattern CASE INSENSITIVE    protected String replaceVarsWithProperties String message        try         StringBuffer newStr   new StringBuffer message         int lenDiff   0        Matcher m   patternMatchForProperties matcher message         while  m find              String fullText   m group 0           String keyName   m group 1           String newValue   System getProperty keyName           String replacementText   newValue          newStr   newStr replace m start   - lenDiff  m end   - lenDiff  replacementText           lenDiff    fullText length   - replacementText length                  return newStr toString          catch  Exception e          return message

User · Answer

I used  String template    Hello  s Please find attached  s which is due on  s    String message   String format template  name  invoiceNumber  dueDate

User · Answer

FYI  In the new language Kotlin  you can use  String Templates  in your source code directly   no 3rd party library or template engine need to do the variable replacement   It is a feature of the language itself   See  https   kotlinlang org docs reference basic-types html string-templates

[java] How to replace a set of tokens in a Java String?

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