Parsing query strings on Android

Question

Java EE has ServletRequest getParameterValues    On non-EE platforms  URL getQuery   simply returns a string  What s the normal way to properly parse the query string in a URL when not on Java EE   It is popular in the answers to try and make your own parser   This is very interesting and exciting micro-coding project  but I cannot say that it is a good idea  The code snippets below are generally flawed or broken  Breaking them is an interesting exercise for the reader  And to the hackers attacking the websites that use them  Parsing query strings is a well defined problem but reading the spec and understanding the nuances is non-trivial  It is far better to let some platform library coder do the hard work  and do the fixing  for you

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On Android   import android net Uri          Uri uri Uri parse url string   uri getQueryParameter  para1

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On Android  the Apache libraries provide a Query parser   http   developer android com reference org apache http client utils URLEncodedUtils html and http   hc apache org httpcomponents-client-ga httpclient apidocs org apache http client utils URLEncodedUtils html

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If you have jetty  server or client  libs on your classpath you can use the jetty util classes  see javadoc   e g    import org eclipse jetty util    URL url   new URL  www example com index php foo bar amp bla blub    MultiMap lt String gt  params   new MultiMap lt String gt     UrlEncoded decodeTo url getQuery    params   UTF-8     assert params getString  foo   equals  bar    assert params getString  bla   equals  blub

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You say  Java  but  not Java EE   Do you mean you are using JSP and or servlets but not a full Java EE stack  If that s the case  then you should still have request getParameter   available to you   If you mean you are writing Java but you are not writing JSPs nor servlets  or that you re just using Java as your reference point but you re on some other platform that doesn t have built-in parameter parsing     Wow  that just sounds like an unlikely question  but if so  the principle would be   xparm 0 word    loop   get next char   if no char     exit loop   if char          param name xparm  word     word      else if char    amp       param value xparm  word     word        xparm xparm 1   else if char          read next two chars     word word interpret the chars as hex digits to make a byte   else     word word char    I could write Java code but that would be pointless  because if you have Java available  you can just use request getParameters

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this method takes the uri and return map of par name and par value    public static Map lt String  String gt  getQueryMap String uri         String queryParms     uri split              Map lt String  String gt  map   new HashMap lt  gt             if  queryParms    null    queryParms length    0  return map       String   params   queryParms 1  split   amp         for  String param   params            String name   param split      0           String value   param split      1           map put name  value             return map

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Guava s Multimap is better suited for this  Here is a short clean version   Multimap lt String  String gt  getUrlParameters String url            try               Multimap lt String  String gt  ret   ArrayListMultimap create                for  NameValuePair param   URLEncodedUtils parse new URI url    UTF-8                      ret put param getName    param getValue                               return ret            catch  URISyntaxException e                throw new RuntimeException e

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Since Android M things have got more complicated  The answer of android net URI getQueryParameter   has a bug which breaks spaces before JellyBean  Apache URLEncodedUtils parse   worked  but was deprecated in L  and removed in M  So the best answer now is UrlQuerySanitizer  This has existed since API level 1 and still exists  It also makes you think about the tricky issues like how do you handle special characters  or repeated values  The simplest code is UrlQuerySanitizer ValueSanitizer sanitizer   UrlQuerySanitizer getAllButNullLegal       remember to decide if you want the first or last parameter with the same name    If you want the first call setPreferFirstRepeatedParameter true   sanitizer parseUrl url   String value   sanitizer getValue  quot paramName quot     If you are happy with the default parsing behavior you can do  new UrlQuerySanitizer url  getValue  quot paramName quot    but you should make sure you understand what the default parsing behavor is  as it might not be what you want

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if  queryString    null        final String   arrParameters   queryString split  quot  amp  quot        for  final String tempParameterString   arrParameters                final String   arrTempParameter   tempParameterString split  quot   quot            if  arrTempParameter length  gt   2                        final String parameterKey   arrTempParameter 0               final String parameterValue   arrTempParameter 1                 do something with the parameters

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On Android its simple as the code below   UrlQuerySanitizer sanitzer   new UrlQuerySanitizer url   String value   sanitzer getValue  your get parameter      Also if you don t want to register each expected query key use   sanitzer setAllowUnregisteredParamaters true    Before calling   sanitzer parseUrl yourUrl

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public static Map lt String  List lt String gt  gt  getUrlParameters String url          throws UnsupportedEncodingException       Map lt String  List lt String gt  gt  params   new HashMap lt String  List lt String gt  gt         String   urlParts   url split  quot     quot        if  urlParts length  gt  1            String query   urlParts 1           for  String param   query split  quot  amp  quot                  String pair     param split  quot   quot   2               String key   URLDecoder decode pair 0    quot UTF-8 quot                String value    quot  quot               if  pair length  gt  1                    value   URLDecoder decode pair 1    quot UTF-8 quot                              List lt String gt  values   params get key               if  values    null                    values   new ArrayList lt String gt                     params put key  values                             values add value                       return params

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Apache AXIS2 has a self-contained implementation of QueryStringParser java  If you are not using Axis2  just download the sourcecode and test case from here -  http   svn apache org repos asf axis axis2 java core trunk modules kernel src org apache axis2 transport http util QueryStringParser java  http   svn apache org repos asf axis axis2 java core trunk modules kernel test org apache axis2 transport http util QueryStringParserTest java

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I have methods to achieve this   1    public static String getQueryString String url  String tag        String   params   url split   amp         Map lt String  String gt  map   new HashMap lt String  String gt         for  String param   params            String name   param split      0           String value   param split      1           map put name  value              Set lt String gt  keys   map keySet        for  String key   keys            if key equals tag             return map get key                     System out println  Name     key           System out println  Value     map get key              return         2  and the easiest way to do this Using Uri class   public static String getQueryString String url  String tag        try           Uri uri Uri parse url           return uri getQueryParameter tag        catch Exception e           Log e TAG  getQueryString       e getMessage               return         and this is an example of how to use either of two methods   String url    http   www jorgesys com advertisements publicidadmobile htm position x46 amp site reform amp awidth 800 amp aheight 120         String tagValue   getQueryString url  awidth      the value of tagValue is 800

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Just for reference  this is what I ve ended up with  based on URLEncodedUtils  and returning a Map    Features    it accepts the query string part of the url  you can use request getQueryString    an empty query string will produce an empty Map a parameter without a value   test  will be mapped to an empty List lt String gt    Code   public static Map lt String  List lt String gt  gt  getParameterMapOfLists String queryString        Map lt String  List lt String gt  gt  mapOfLists   new HashMap lt String  List lt String gt  gt         if  queryString    null    queryString length      0            return mapOfLists            List lt NameValuePair gt  list   URLEncodedUtils parse URI create  http   localhost      queryString    UTF-8        for  NameValuePair pair   list            List lt String gt  values   mapOfLists get pair getName             if  values    null                values   new ArrayList lt String gt                 mapOfLists put pair getName    values                     if  pair getValue      null                values add pair getValue                          return mapOfLists      A compatibility helper  values are stored in a String array just as in ServletRequest getParameterMap      public static Map lt String  String   gt  getParameterMap String queryString        Map lt String  List lt String gt  gt  mapOfLists   getParameterMapOfLists queryString        Map lt String  String   gt  mapOfArrays   new HashMap lt String  String   gt         for  String key   mapOfLists keySet              mapOfArrays put key  mapOfLists get key  toArray new String                    return mapOfArrays

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Parsing the query string is a bit more complicated than it seems  depending on how forgiving you want to be   First  the query string is ascii bytes   You read in these bytes one at a time and convert them to characters   If the character is   or  amp  then it signals the start of a parameter name   If the character is   then it signals the start of a paramter value   If the character is   then it signals the start of an encoded byte   Here is where it gets tricky   When you read in a   char you have to read the next two bytes and interpret them as hex digits   That means the next two bytes will be 0-9  a-f or A-F   Glue these two hex digits together to get your byte value   But remember  bytes are not characters   You have to know what encoding was used to encode the characters   The character    does not encode the same in UTF-8 as it does in ISO-8859-1   In general it s impossible to know what encoding was used for a given character set   I always use UTF-8 because my web site is configured to always serve everything using UTF-8 but in practice you can t be certain   Some user-agents will tell you the character encoding in the request  you can try to read that if you have a full HTTP request   If you just have a url in isolation  good luck   Anyway  assuming you are using UTF-8 or some other multi-byte character encoding  now that you ve decoded one encoded byte you have to set it aside until you capture the next byte   You need all the encoded bytes that are together because you can t url-decode properly one byte at a time   Set aside all the bytes that are together then decode them all at once to reconstruct your character   Plus it gets more fun if you want to be lenient and account for user-agents that mangle urls   For example  some webmail clients double-encode things   Or double up the   amp   chars  for example   http   yoursite com blah  p1  v1 amp  amp p2  v2    If you want to try to gracefully deal with this  you will need to add more logic to your parser

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On Android  you can use the Uri parse static method of the android net Uri class to do the heavy lifting   If you re doing anything with URIs and Intents you ll want to use it anyways

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I don t think there is one in JRE  You can find similar functions in other packages like Apache HttpClient  If you don t use any other packages  you just have to write your own  It s not that hard  Here is what I use   public class QueryString     private Map lt String  List lt String gt  gt  parameters    public QueryString String qs      parameters   new TreeMap lt String  List lt String gt  gt           Parse query string      String pairs     qs split   amp          for  String pair   pairs                String name              String value              int pos   pair indexOf                      for  n    the value is     for  n   the value is null          if  pos    -1              name   pair            value   null             else          try           name   URLDecoder decode pair substring 0  pos    UTF-8                  value   URLDecoder decode pair substring pos 1  pair length      UTF-8                         catch  UnsupportedEncodingException e               Not really possible  throw unchecked            throw new IllegalStateException  No UTF-8                                 List lt String gt  list   parameters get name            if  list    null              list   new ArrayList lt String gt               parameters put name  list                       list add value               public String getParameter String name              List lt String gt  values   parameters get name     if  values    null     return null     if  values size      0     return        return values get 0        public String   getParameterValues String name              List lt String gt  values   parameters get name     if  values    null     return null     return  String   values toArray new String values size           public Enumeration lt String gt  getParameterNames         return Collections enumeration parameters keySet           public Map lt String  String   gt  getParameterMap       Map lt String  String   gt  map   new TreeMap lt String  String   gt       for  Map Entry lt String  List lt String gt  gt  entry   parameters entrySet         List lt String gt  list   entry getValue       String   values     if  list    null      values   null     else     values    String    list toArray new String list size         map put entry getKey    values         return map

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If you re using Spring 3 1 or greater  yikes  was hoping that support went back further   you can use the UriComponents and UriComponentsBuilder   UriComponents components   UriComponentsBuilder fromUri uri  build    List lt String gt  myParam   components getQueryParams   get  myParam      components getQueryParams   returns a MultiValueMap lt String  String gt   Here s some more documentation

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Use Apache HttpComponents and wire it up with some collection code to access params by value  http   www joelgerard com 2012 09 14 parsing-query-strings-in-java-and-accessing-values-by-key

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Origanally answered here  On Android  there is Uri class in package android net   Note that Uri is part of android net  while URI is part of java net    Uri class has many functions to extract query key-value pairs    Following function returns key-value pairs in the form of HashMap   In Java   Map lt String  String gt  getQueryKeyValueMap Uri uri       HashMap lt String  String gt  keyValueMap   new HashMap        String key      String value       Set lt String gt  keyNamesList   uri getQueryParameterNames        Iterator iterator   keyNamesList iterator         while  iterator hasNext             key    String  iterator next            value   uri getQueryParameter key           keyValueMap put key  value             return keyValueMap      In Kotlin   fun getQueryKeyValueMap uri  Uri   HashMap lt String  String gt            val keyValueMap   HashMap lt String  String gt            var key  String         var value  String          val keyNamesList   uri queryParameterNames         val iterator   keyNamesList iterator            while  iterator hasNext                  key   iterator next   as String             value   uri getQueryParameter key  as String             keyValueMap put key  value                    return keyValueMap

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Answering here because this is a popular thread   This is a clean solution in Kotlin that uses the recommended UrlQuerySanitizer api  See the official documentation   I have added a string builder to concatenate and display the params        var myURL  String    null        if the url is sent from a different activity where you set it to a value     if  intent hasExtra  my value              myURL   intent extras getString  my value         else           myURL   intent dataString            val sanitizer   UrlQuerySanitizer myURL         We don t want to manually define every expected query  key   so we set this to true     sanitizer allowUnregisteredParamaters   true     val parameterNamesToValues  List lt UrlQuerySanitizer ParameterValuePair gt    sanitizer parameterList     val parameterIterator  Iterator lt UrlQuerySanitizer ParameterValuePair gt    parameterNamesToValues iterator           Helper simply so we can display all values on screen     val stringBuilder   StringBuilder        while  parameterIterator hasNext              val parameterValuePair  UrlQuerySanitizer ParameterValuePair   parameterIterator next           val parameterName  String   parameterValuePair mParameter         val parameterValue  String   parameterValuePair mValue             Append string to display all key value pairs         stringBuilder append  Key   parameterName nValue   parameterValue n n                 Set a textView s text to display the string     val paramListString   stringBuilder toString       val textView  TextView   findViewById R id activity title  as TextView     textView text    Paramlist is  n n paramListString          to check if the url has specific keys     if  sanitizer hasParameter  type              val type   sanitizer getValue  type           println  sanitizer has type param  type

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using Guava   Multimap lt String String gt  parseQueryString String queryString  String encoding        LinkedListMultimap lt String  String gt  result   LinkedListMultimap create         for String entry   Splitter on   amp    omitEmptyStrings   split queryString             String pair      entry split      2           try               result put URLDecoder decode pair 0   encoding   pair length    2   URLDecoder decode pair 1   encoding    null             catch  UnsupportedEncodingException e                throw new RuntimeException e                        return result

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public static Map  lt String  String gt  parseQueryString  final URL url          throws UnsupportedEncodingException       final Map  lt String  String gt  qps   new TreeMap  lt String  String gt          final StringTokenizer pairs   new StringTokenizer  url getQuery       amp         while  pairs hasMoreTokens                   final String pair   pairs nextToken             final StringTokenizer parts   new StringTokenizer  pair                final String name   URLDecoder decode  parts nextToken      ISO-8859-1            final String value   URLDecoder decode  parts nextToken      ISO-8859-1            qps put  name  value             return qps

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On Android  I tried using  diyism answer but I encountered the space character issue raised by  rpetrich  for example  I fill out a form where username    us us  and password    pw pw  causing a URL string to look like   http   somewhere username us 2Bus amp password pw pw   However   diyism code returns  us us  and  pw pw   i e  it doesn t detect the space character  If the URL was rewritten with  20 the space character gets identified   http   somewhere username us 2Bus amp password pw 20pw   This leads to the following fix   Uri uri   Uri parse url string replace        20     uri getQueryParameter  para1

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This works for me   I m not sure why every one was after a Map  List  All I needed was a simple name value Map   To keep things simple I used the build in URI getQuery      public static Map lt String  String gt  getUrlParameters URI uri      throws UnsupportedEncodingException       Map lt String  String gt  params   new HashMap lt String  String gt         for  String param   uri getQuery   split   amp               String pair     param split               String key   URLDecoder decode pair 0    UTF-8            String value               if  pair length  gt  1                value   URLDecoder decode pair 1    UTF-8                      params put new String key   new String value              return params

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For a servlet or a JSP page you can get querystring key value pairs by using request getParameter  paramname    String name   request getParameter  name      There are other ways of doing it but that s the way I do it in all the servlets and jsp pages that I create

[java] Parsing query strings on Android

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