How can I append a query parameter to an existing URL

Question

I d like to append key-value pair as a query parameter to an existing URL  While I could do this by checking for the existence of whether the URL has a query part or a fragment part and doing the append by jumping though a bunch of if-clauses but I was wondering if there was clean way if doing this through the Apache Commons libraries or something equivalent   http   example com would be http   example com name John  http   example com fragment would be http   example com name John fragment  http   example com email john doe email com would be http   example com email john doe email com amp name John  http   example com email john doe email com fragment would be http   example com email john doe email com amp name John fragment  I ve run this scenario many times before and I d like to do this without breaking the URL in any way

User · Answer

Use the URI class   Create a new URI with your existing String to  break it up  to parts  and instantiate another one to assemble the modified url   URI u   new URI  http   example com email john email com amp name John fragment        Modify the query  append your new parameter StringBuilder sb   new StringBuilder u getQuery      null        u getQuery     if  sb length    gt  0      sb append   amp     sb append URLEncoder encode  paramName    UTF-8     sb append       sb append URLEncoder encode  paramValue    UTF-8         Build the new url with the modified query  URI u2   new URI u getScheme    u getAuthority    u getPath        sb toString    u getFragment

User · Answer

For android  Use  https   developer android com reference android net Uri buildUpon   URI oldUri   new URI uri   Uri Builder builder   oldUri buildUpon     builder appendQueryParameter  quot newParameter quot    quot dummyvalue quot     Uri newUri    builder build

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Kotlin  amp  clean  so you don t have to refactor before code review   private fun addQueryParameters url  String    String            val uri   URI url           val queryParams   StringBuilder uri query orEmpty            if  queryParams isNotEmpty                queryParams append   amp             queryParams append URLEncoder encode   QUERY PARAM  param   Xml Encoding UTF 8 name           return URI uri scheme  uri authority  uri path  queryParams toString    uri fragment  toString

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There are plenty of libraries that can help you with URI building  don t reinvent the wheel   Here are three to get you started     Java EE 7    import javax ws rs core UriBuilder      return UriBuilder fromUri url  queryParam key  value  build        org apache httpcomponents httpclient 4 5 2    import org apache http client utils URIBuilder      return new URIBuilder url  addParameter key  value  build        org springframework spring-web 4 2 5 RELEASE    import org springframework web util UriComponentsBuilder      return UriComponentsBuilder fromUriString url  queryParam key  value  build   toUri        See also  GIST   URI Builder Tests

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An update to Adam s answer considering tryp s answer too  Don t have to instantiate a String in the loop   public static URI appendUri String uri  Map lt String  String gt  parameters  throws URISyntaxException       URI oldUri   new URI uri       StringBuilder queries   new StringBuilder         for Map Entry lt String  String gt  query  parameters entrySet              queries append    amp     query getKey       query getValue                String newQuery   oldUri getQuery        if  newQuery    null            newQuery   queries substring 1         else           newQuery    queries toString               URI newUri   new URI oldUri getScheme    oldUri getAuthority                oldUri getPath    newQuery  oldUri getFragment          return newUri

User · Answer

This can be done by using the java net URI class to construct a new instance using the parts from an existing one  this should ensure it conforms to URI syntax   The query part will either be null or an existing string  so you can decide to append another parameter with  amp  or start a new query   public class StackOverflow26177749        public static URI appendUri String uri  String appendQuery  throws URISyntaxException           URI oldUri   new URI uri            String newQuery   oldUri getQuery            if  newQuery    null                newQuery   appendQuery            else               newQuery      amp     appendQuery                       return new URI oldUri getScheme    oldUri getAuthority                    oldUri getPath    newQuery  oldUri getFragment                public static void main String   args  throws Exception           System out println appendUri  http   example com    name John             System out println appendUri  http   example com fragment    name John             System out println appendUri  http   example com email john doe email com    name John             System out println appendUri  http   example com email john doe email com fragment    name John               Shorter alternative  public static URI appendUri String uri  String appendQuery  throws URISyntaxException       URI oldUri   new URI uri       return new URI oldUri getScheme    oldUri getAuthority    oldUri getPath                oldUri getQuery      null   appendQuery   oldUri getQuery       amp     appendQuery  oldUri getFragment         Output  http   example com name John http   example com name John fragment http   example com email john doe email com amp name John http   example com email john doe email com amp name John fragment

User · Answer

I suggest an improvement of the Adam s answer accepting HashMap as parameter         Append parameters to given url     param url     param parameters     return new String url with given parameters     throws URISyntaxException     public static String appendToUrl String url  HashMap lt String  String gt  parameters  throws URISyntaxException       URI uri   new URI url       String query   uri getQuery         StringBuilder builder   new StringBuilder         if  query    null          builder append query        for  Map Entry lt String  String gt  entry  parameters entrySet                  String keyValueParam   entry getKey           entry getValue            if   builder toString   isEmpty                builder append   amp              builder append keyValueParam              URI newUri   new URI uri getScheme    uri getAuthority    uri getPath    builder toString    uri getFragment         return newUri toString

[java] How can I append a query parameter to an existing URL?

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