Sending HTTP POST Request In Java

Question

lets assume this URL     http   www example com page php id 10                Here id needs to be sent in a POST request   I want to send the id   10 to the server s page php  which accepts it in a POST method   How can i do this from within Java   I tried this    URL aaa   new URL  http   www example com page php    URLConnection ccc   aaa openConnection      But I still can t figure out how to send it via POST

User · Answer

The first answer was great  but I had to add try catch to avoid Java compiler errors  Also  I had troubles to figure how to read the HttpResponse with Java libraries     Here is the more complete code          Create the POST request     HttpClient httpClient   new DefaultHttpClient    HttpPost httpPost   new HttpPost  http   example com        Request parameters and other properties  List lt NameValuePair gt  params   new ArrayList lt NameValuePair gt     params add new BasicNameValuePair  user    Bob     try       httpPost setEntity new UrlEncodedFormEntity params   UTF-8       catch  UnsupportedEncodingException e           writing error to Log     e printStackTrace            Execute the HTTP Request     try       HttpResponse response   httpClient execute httpPost       HttpEntity respEntity   response getEntity         if  respEntity    null               EntityUtils to get the response content         String content    EntityUtils toString respEntity           catch  ClientProtocolException e           writing exception to log     e printStackTrace      catch  IOException e           writing exception to log     e printStackTrace

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Sending a POST request is easy in vanilla Java  Starting with a URL  we need t convert it to a URLConnection using url openConnection     After that  we need to cast it to a HttpURLConnection  so we can access its setRequestMethod   method to set our method  We finally say that we are going to send data over the connection   URL url   new URL  https   www example com login    URLConnection con   url openConnection    HttpURLConnection http    HttpURLConnection con  http setRequestMethod  POST       PUT is another valid option http setDoOutput true     We then need to state what we are going to send   Sending a simple form  A normal POST coming from a http form has a well defined format  We need to convert our input to this format   Map lt String String gt  arguments   new HashMap lt  gt     arguments put  username    root    arguments put  password    sjh76HSn        This is a fake password obviously StringJoiner sj   new StringJoiner   amp     for Map Entry lt String String gt  entry   arguments entrySet        sj add URLEncoder encode entry getKey     UTF-8                     URLEncoder encode entry getValue     UTF-8     byte   out   sj toString   getBytes StandardCharsets UTF 8   int length   out length    We can then attach our form contents to the http request with proper headers and send it   http setFixedLengthStreamingMode length   http setRequestProperty  Content-Type    application x-www-form-urlencoded  charset UTF-8    http connect    try OutputStream os   http getOutputStream          os write out        Do something with http getInputStream       Sending JSON  We can also send json using java  this is also easy   byte   out       username     root     password     password      getBytes StandardCharsets UTF 8   int length   out length   http setFixedLengthStreamingMode length   http setRequestProperty  Content-Type    application json  charset UTF-8    http connect    try OutputStream os   http getOutputStream          os write out        Do something with http getInputStream     Remember that different servers accept different content-types for json  see this question     Sending files with java post  Sending files can be considered more challenging to handle as the format is more complex  We are also going to add support for sending the files as a string  since we don t want to buffer the file fully into the memory   For this  we define some helper methods   private void sendFile OutputStream out  String name  InputStream in  String fileName        String o    Content-Disposition  form-data  name       URLEncoder encode name  UTF-8                        filename       URLEncoder encode filename  UTF-8         r n r n       out write o getBytes StandardCharsets UTF 8        byte   buffer   new byte 2048       for  int n   0  n  gt   0  n   in read buffer           out write buffer  0  n       out write   r n  getBytes StandardCharsets UTF 8       private void sendField OutputStream out  String name  String field        String o    Content-Disposition  form-data  name                     URLEncoder encode name  UTF-8         r n r n       out write o getBytes StandardCharsets UTF 8        out write URLEncoder encode field  UTF-8   getBytes StandardCharsets UTF 8        out write   r n  getBytes StandardCharsets UTF 8        We can then use these methods to create a multipart post request as follows   String boundary   UUID randomUUID   toString    byte   boundaryBytes                 --    boundary     r n   getBytes StandardCharsets UTF 8   byte   finishBoundaryBytes                 --    boundary    --   getBytes StandardCharsets UTF 8   http setRequestProperty  Content-Type                multipart form-data  charset UTF-8  boundary     boundary       Enable streaming mode with default settings http setChunkedStreamingMode 0        Send our fields  try OutputStream out   http getOutputStream             Send our header  thx Algoman      out write boundaryBytes           Send our first field     sendField out   username    root            Send a seperator     out write boundaryBytes           Send our second field     sendField out   password    toor            Send another seperator     out write boundaryBytes           Send our file     try InputStream file   new FileInputStream  test txt              sendFile out   identification   file   text txt                  Finish the request     out write finishBoundaryBytes          Do something with http getInputStream

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Updated Answer   Since some of the classes  in the original answer  are deprecated in the newer version of Apache HTTP Components  I m posting this update   By the way  you can access the full documentation for more examples here   HttpClient httpclient   HttpClients createDefault    HttpPost httppost   new HttpPost  http   www a-domain com foo         Request parameters and other properties  List lt NameValuePair gt  params   new ArrayList lt NameValuePair gt  2   params add new BasicNameValuePair  param-1    12345     params add new BasicNameValuePair  param-2    Hello      httppost setEntity new UrlEncodedFormEntity params   UTF-8        Execute and get the response  HttpResponse response   httpclient execute httppost   HttpEntity entity   response getEntity     if  entity    null        try  InputStream instream   entity getContent                 do something useful           Original Answer   I recommend to use Apache HttpClient  its faster and easier to implement   HttpPost post   new HttpPost  http   jakarata apache org     NameValuePair   data         new NameValuePair  user    joe        new NameValuePair  password    bloggs      post setRequestBody data      execute method and handle any error responses      InputStream in   post getResponseBodyAsStream       handle response    for more information check this url  http   hc apache org

User · Answer

simplest way to send parameters with the post request   String postURL    http   www example com page php    HttpPost post   new HttpPost postURL    List lt NameValuePair gt  params   new ArrayList lt NameValuePair gt     params add new BasicNameValuePair  id    10      UrlEncodedFormEntity ent   new UrlEncodedFormEntity params   UTF-8    post setEntity ent    HttpClient client   new DefaultHttpClient    HttpResponse responsePOST   client execute post     You have done  now you can use responsePOST  Get response content as string   BufferedReader reader   new BufferedReader new  InputStreamReader responsePOST getEntity   getContent     2048    if  responsePOST    null        StringBuilder sb   new StringBuilder        String line      while   line   reader readLine       null            System out println   line       line           sb append line             String getResponseString           getResponseString   sb toString      use server output getResponseString as string value

User · Answer

Call HttpURLConnection setRequestMethod  POST   and HttpURLConnection setDoOutput true   Actually only the latter is needed as POST then becomes the default method

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String rawData    id 10   String type    application x-www-form-urlencoded   String encodedData   URLEncoder encode  rawData   UTF-8      URL u   new URL  http   www example com page php    HttpURLConnection conn    HttpURLConnection  u openConnection    conn setDoOutput true   conn setRequestMethod  POST    conn setRequestProperty   Content-Type   type    conn setRequestProperty   Content-Length   String valueOf encodedData length      OutputStream os   conn getOutputStream    os write encodedData getBytes

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I recomend use http-request built on apache http api   HttpRequest lt String gt  httpRequest   HttpRequestBuilder createPost  http   www example com page php   String class   responseDeserializer ResponseDeserializer ignorableDeserializer    build     public void send       String response   httpRequest execute  id    10   get

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A simple way using Apache HTTP Components is  Request Post  http   www example com page php                bodyForm Form form   add  id    10   build                 execute                returnContent      Take a look at the Fluent API

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I suggest using Postman to generate the request code  Simply make the request using Postman then hit the code tab   Then you ll get the following window to choose in which language you want your request code to be

[java] Sending HTTP POST Request In Java

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