How to convert map to url query string

Question

Do you know of any utility class library  that can convert Map into URL-friendly query string   Example   I have a map    param1  12   param2   cat    I want to get    param1 12 amp param2 cat   final output  relativeUrl param1 12 amp param2 cat

User · Answer

Here s something that I quickly wrote  I m sure it can be improved upon   import java util    import java io UnsupportedEncodingException  import java net URLEncoder   public class MapQuery       static String urlEncodeUTF8 String s            try               return URLEncoder encode s   UTF-8              catch  UnsupportedEncodingException e                throw new UnsupportedOperationException e                       static String urlEncodeUTF8 Map lt     gt  map            StringBuilder sb   new StringBuilder            for  Map Entry lt     gt  entry   map entrySet                  if  sb length    gt  0                    sb append   amp                               sb append String format   s  s                   urlEncodeUTF8 entry getKey   toString                     urlEncodeUTF8 entry getValue   toString                                      return sb toString                     public static void main String   args            Map lt String Object gt  map   new HashMap lt String Object gt             map put  p1   12           map put  p2    cat            map put  p3    a  amp  b                     System out println urlEncodeUTF8 map               prints  p3 a  26 b amp p2 cat amp p1 12

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I think this is better for memory usage and performance  and I want to send just the property name when the value is null   public static String toUrlEncode Map lt String  Object gt  map        StringBuilder sb   new StringBuilder        map entrySet   stream                forEach entry                     - gt   entry getValue      null                       sb append entry getKey                          sb append entry getKey                                 append                                   append URLEncoder encode entry getValue   toString    StandardCharsets UTF 8                         append   amp                       sb delete sb length   - 1  sb length         return sb toString

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I found a smooth solution using java 8 and polygenelubricants  solution   parameters entrySet   stream        map p - gt  urlEncodeUTF8 p getKey            urlEncodeUTF8 p getValue          reduce  p1  p2  - gt  p1     amp     p2       orElse

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There s nothing built into java to do this  But  hey  java is a programming language  so   let s program it  map entrySet   stream   map e - gt  e getKey      quot   quot    e getValue    collect Collectors joining  quot  amp  quot     This gives you  quot param1 12 amp param2 cat quot   Now we need to join the URL and this bit together  You d think you can just do  URL    quot   quot    theAbove but if the URL already contains a question mark  you have to join it all together with  quot  amp  quot  instead  One way to check is to see if there s a question mark in the URL someplace already  Also  I don t quite know what is in your map  If it s raw stuff  you probably have to safeguard the call to e getKey   and e getValue   with URLEncoder encode or similar  Yet another way to go is that you take a wider view  Are you trying to append a map s content to a URL  or    are you trying to make an HTTP S  request from a java process with the stuff in the map as  additional  HTTP params  In the latter case  you can look into an http library like OkHttp which has some nice APIs to do this job  then you can forego any need to mess about with that URL in the first place

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Personally  I d go for a solution like this  it s incredibly similar to the solution provided by  rzwitserloot  only subtle differences    This solution is small  simple  amp  clean  it requires very little in terms of dependencies  all of which are a part of the Java Util package   Map lt String  String gt  map   new HashMap lt  gt      map put  param1    12    map put  param2    cat     String output    someUrl    output    map entrySet        stream        map x - gt  x getKey           x getValue       amp         collect Collectors joining   amp       System out println output substring 0  output length   -1

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This is the solution I implemented  using Java 8 and org apache http client URLEncodedUtils  It maps the entries of the map into a list of BasicNameValuePair and then uses Apache s URLEncodedUtils to turn that into a query string   List lt BasicNameValuePair gt  nameValuePairs   params entrySet   stream       map entry - gt  new BasicNameValuePair entry getKey    entry getValue         collect Collectors toList      URLEncodedUtils format nameValuePairs  Charset forName  UTF-8

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Using EntrySet and Streams    map    entrySet      stream      map e - gt  e getKey           e getValue       collect Collectors joining   amp

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If you actually want to build a complete URI  try URIBuilder from Apache Http Compoments  HttpClient 4    This does not actually answer the question  but it answered the one I had when I found this question

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Update June 2016  Felt compelled to add an answer having seen far too many SOF answers with dated or inadequate answers to very common problem - a good library and some solid example usage for both parse and format operations   Use org apache httpcomponents httpclient library  The library contains this org apache http client utils URLEncodedUtils class utility   For example  it is easy to download this dependency from Maven     lt dependency gt       lt groupId gt org apache httpcomponents lt  groupId gt       lt artifactId gt httpclient lt  artifactId gt       lt version gt 4 5 lt  version gt    lt  dependency gt    For my purposes I only needed to parse  read from query string to name-value pairs  and format  read from name-value pairs to query string  query strings  However  there are equivalents for doing the same with a URI  see commented out line below       Required imports  import org apache http NameValuePair  import org apache http client utils URLEncodedUtils  import java io UnsupportedEncodingException  import java net URLDecoder  import java nio charset StandardCharsets       code snippet  public static void parseAndFormatExample   throws UnsupportedEncodingException           final String queryString    nonce 12345 amp redirectCallbackUrl http   www bbc co uk           System out println queryString                gt  nonce 12345 amp redirectCallbackUrl http   www bbc co uk          final List lt NameValuePair gt  params                   URLEncodedUtils parse queryString  StandardCharsets UTF 8              List lt NameValuePair gt  params   URLEncodedUtils parse new URI url    UTF-8             for  final NameValuePair param   params                System out println param getName             param getValue                      gt  nonce   12345                  gt  redirectCallbackUrl   http   www bbc co uk                    final String newQueryStringEncoded                   URLEncodedUtils format params  StandardCharsets UTF 8                decode when printing to screen         final String newQueryStringDecoded                   URLDecoder decode newQueryStringEncoded  StandardCharsets UTF 8 toString             System out println newQueryStringDecoded                gt  nonce 12345 amp redirectCallbackUrl http   www bbc co uk         This library did exactly what I needed and was able to replace some hacked custom code

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Kotlin mapOf     quot param1 quot  to 12     quot param2 quot  to  quot cat quot    map    quot   it key    it value  quot       joinToString  quot  amp  quot

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The most robust one I saw off-the-shelf is the URLEncodedUtils class from Apache Http Compoments  HttpClient 4 0    The method URLEncodedUtils format   is what you need   It doesn t use map so you can have duplicate parameter names  like     a 1 amp a 2 amp b 3   Not that I recommend this kind of use of parameter names

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For multivalue map you can do like below  using java 8 stream api s  Url encoding has been taken cared in this  MultiValueMap lt String  String gt  params    new LinkedMultiValueMap lt  gt     String urlQueryString   params entrySet                stream                flatMap stringListEntry - gt  stringListEntry getValue                        stream                        map s - gt  UriUtils encode stringListEntry getKey    StandardCharsets UTF 8 toString       quot   quot                                UriUtils encode s  StandardCharsets UTF 8 toString                   collect Collectors joining  quot  amp  quot

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To improve a little bit upon  eclipse s answer  In Javaland a request parameter map is usually represented as a Map lt String  String   gt   a Map lt String  List lt String gt  gt  or possibly some kind of MultiValueMap lt String  String gt  which is sort of the same thing  In any case  a parameter can usually have multiple values  A Java 8 solution would therefore be something along these lines   public String getQueryString HttpServletRequest request  String encoding        Map lt String  String   gt  parameters   request getParameterMap         return parameters entrySet   stream                flatMap entry - gt  encodeMultiParameter entry getKey    entry getValue    encoding                reduce  param1  param2  - gt  param1     amp     param2               orElse         private Stream lt String gt  encodeMultiParameter String key  String   values  String encoding        return Stream of values  map value - gt  encodeSingleParameter key  value  encoding       private String encodeSingleParameter String key  String value  String encoding        return urlEncode key  encoding          urlEncode value  encoding      private String urlEncode String value  String encoding        try           return URLEncoder encode value  encoding         catch  UnsupportedEncodingException e            throw new IllegalArgumentException  Cannot url encode     value  e

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I wanted to build on  eclipse s answer using java 8 mapping and reducing    protected String formatQueryParams Map lt String  String gt  params          return params entrySet   stream              map p - gt  p getKey           p getValue               reduce  p1  p2  - gt  p1     amp     p2             map s - gt        s             orElse            The extra map operation takes the reduced string and puts a   in front only if the string exists

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Another  one class  no dependency way of doing it  handling single multiple   import java io UnsupportedEncodingException  import java net URLEncoder  import java util ArrayList  import java util Arrays  import java util Iterator  import java util LinkedHashMap  import java util List  import java util Map  import java util Map Entry   public class UrlQueryString     private static final String DEFAULT ENCODING    UTF-8      public static String buildQueryString final LinkedHashMap lt String  Object gt  map        try         final Iterator lt Map Entry lt String  Object gt  gt  it   map entrySet   iterator          final StringBuilder sb   new StringBuilder map size     8         while  it hasNext              final Map Entry lt String  Object gt  entry   it next            final String key   entry getKey            if  key    null              sb append URLEncoder encode key  DEFAULT ENCODING              sb append                 final Object value   entry getValue              final String valueAsString   value    null   URLEncoder encode value toString    DEFAULT ENCODING                  sb append valueAsString             if  it hasNext                  sb append   amp                           else                Do what you want   for example            assert false   String format  Null key in query map   s   map entrySet                             return sb toString          catch  final UnsupportedEncodingException e          throw new UnsupportedOperationException e                public static String buildQueryStringMulti final LinkedHashMap lt String  List lt Object gt  gt  map        try         final StringBuilder sb   new StringBuilder map size     8         for  final Iterator lt Entry lt String  List lt Object gt  gt  gt  mapIterator   map entrySet   iterator    mapIterator hasNext               final Entry lt String  List lt Object gt  gt  entry   mapIterator next            final String key   entry getKey            if  key    null              final String keyEncoded   URLEncoder encode key  DEFAULT ENCODING             final List lt Object gt  values   entry getValue              sb append keyEncoded             sb append                 if  values    null                for  final Iterator lt Object gt  listIt   values iterator    listIt hasNext                     final Object valueObject   listIt next                  sb append valueObject    null   URLEncoder encode valueObject toString    DEFAULT ENCODING                       if  listIt hasNext                      sb append   amp                     sb append keyEncoded                   sb append                                                           if  mapIterator hasNext                  sb append   amp                           else                Do what you want   for example            assert false   String format  Null key in query map   s   map entrySet                             return sb toString          catch  final UnsupportedEncodingException e          throw new UnsupportedOperationException e                public static void main final String   args           Examples  could be turned into unit tests                 final LinkedHashMap lt String  Object gt  queryItems   new LinkedHashMap lt String  Object gt           queryItems put  brand    C amp A          queryItems put  count   null         queryItems put  misc   42         final String buildQueryString   buildQueryString queryItems         System out println buildQueryString                     final LinkedHashMap lt String  List lt Object gt  gt  queryItems   new LinkedHashMap lt String  List lt Object gt  gt           queryItems put  usernames   new ArrayList lt Object gt  Arrays asList new String      bob    john              queryItems put  nullValue   null         queryItems put  misc   new ArrayList lt Object gt  Arrays asList new Integer     1  2  3             final String buildQueryString   buildQueryStringMulti queryItems         System out println buildQueryString                 You may use either simple  easier to write in most cases  or multiple when required  Note that both can be combined by adding an ampersand    If you find any problems let me know in the comments

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In Spring Util  there is a better way     import org springframework util LinkedMultiValueMap  import org springframework util MultiValueMap  import org springframework util concurrent ListenableFuture  import org springframework web util UriComponents  import org springframework web util UriComponentsBuilder   MultiValueMap lt String  String gt  params   new LinkedMultiValueMap lt String  String gt     params add  key   key   params add  storeId   storeId   params add  orderId   orderId   UriComponents uriComponents       UriComponentsBuilder fromHttpUrl  http   spsenthil com order   queryParams params  build    ListenableFuture lt ResponseEntity lt String gt  gt  responseFuture       restTemplate getForEntity uriComponents toUriString    String class

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You can use a Stream for this  but instead of appending query parameters myself I d use a Uri Builder  For example   final Map lt String  String gt  map   new HashMap lt  gt     map put  param1    cat    map put  param2    12     final Uri uri        map entrySet   stream   collect             - gt  Uri parse  relativeUrl   buildUpon             builder  e  - gt  builder appendQueryParameter e getKey    e getValue              b1  b2  - gt    throw new UnsupportedOperationException            build       Or  if you consider it more readable    final Uri Builder builder   Uri parse  relativeUrl   buildUpon    map entrySet   forEach e - gt  builder appendQueryParameter e getKey    e getValue    final Uri uri   builder build                assertEquals Uri parse  relativeUrl param1 cat amp param2 12    uri

[java] How to convert map to url query string?

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