How to send HTTP request in java

Question

In Java  How to compose a HTTP request message and send it to a HTTP WebServer

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Here s a complete Java 7 program   class GETHTTPResource     public static void main String   args  throws Exception       try  java util Scanner s   new java util Scanner new java net URL  http   tools ietf org rfc rfc768 txt   openStream             System out println s useDelimiter    A   next                   The new try-with-resources will auto-close the Scanner  which will auto-close the InputStream

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This will help you  Don t forget to add the JAR HttpClient jar to the classpath   import java io FileOutputStream  import java io IOException   import org apache commons httpclient HttpClient  import org apache commons httpclient HttpStatus  import org apache commons httpclient NameValuePair  import org apache commons httpclient methods PostMethod   public class MainSendRequest         static String url             http   localhost 8080 HttpRequestSample RequestSend jsp        public static void main String   args               Instantiate an HttpClient         HttpClient client   new HttpClient               Instantiate a GET HTTP method         PostMethod method   new PostMethod url           method setRequestHeader  Content-type                    text xml  charset ISO-8859-1               Define name-value pairs to set into the QueryString         NameValuePair nvp1  new NameValuePair  firstName   fname            NameValuePair nvp2  new NameValuePair  lastName   lname            NameValuePair nvp3  new NameValuePair  email   email email com             method setQueryString new NameValuePair   nvp1 nvp2 nvp3             try              int statusCode   client executeMethod method                System out println  Status Code     statusCode               System out println  QueryString gt  gt  gt    method getQueryString                 System out println  Status Text gt  gt  gt                      HttpStatus getStatusText statusCode                   Get data as a String             System out println method getResponseBodyAsString                    OR as a byte array             byte    res    method getResponseBody                   write to file             FileOutputStream fos  new FileOutputStream  donepage html                fos write res                  release connection             method releaseConnection                      catch IOException e                e printStackTrace

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Google java http client has nice API for http requests  You can easily add JSON support etc  Although for simple request it might be overkill   import com google api client http GenericUrl  import com google api client http HttpRequest  import com google api client http HttpResponse  import com google api client http HttpTransport  import com google api client http javanet NetHttpTransport  import java io IOException  import java io InputStream   public class Network        static final HttpTransport HTTP TRANSPORT   new NetHttpTransport         public void getRequest String reqUrl  throws IOException           GenericUrl url   new GenericUrl reqUrl           HttpRequest request   HTTP TRANSPORT createRequestFactory   buildGetRequest url           HttpResponse response   request execute            System out println response getStatusCode              InputStream is   response getContent            int ch          while   ch   is read       -1                System out print  char  ch                     response disconnect

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I know others will recommend Apache s http-client  but it adds complexity  i e   more things that can go wrong  that is rarely warranted  For a simple task  java net URL will do   URL url   new URL  http   www y com url    InputStream is   url openStream    try        Now read the retrieved document from the stream             finally     is close

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There s a great link about sending a POST request here by Example Depot    try          Construct data     String data   URLEncoder encode  key1    UTF-8           URLEncoder encode  value1    UTF-8        data      amp     URLEncoder encode  key2    UTF-8           URLEncoder encode  value2    UTF-8            Send data     URL url   new URL  http   hostname 80 cgi        URLConnection conn   url openConnection        conn setDoOutput true       OutputStreamWriter wr   new OutputStreamWriter conn getOutputStream         wr write data       wr flush            Get the response     BufferedReader rd   new BufferedReader new InputStreamReader conn getInputStream          String line      while   line   rd readLine       null               Process line              wr close        rd close      catch  Exception e        If you want to send a GET request you can modify the code slightly to suit your needs  Specifically you have to add the parameters inside the constructor of the URL  Then  also comment out this wr write data    One thing that s not written and you should beware of  is the timeouts  Especially if you want to use it in WebServices you have to set timeouts  otherwise the above code will wait indefinitely or for a very long time at least and it s something presumably you don t want    Timeouts are set like this conn setReadTimeout 2000   the input parameter is in milliseconds

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You can use java net HttpUrlConnection   Example  from here   with improvements  Included in case of link rot   public static String executePost String targetURL  String urlParameters      HttpURLConnection connection   null     try         Create connection     URL url   new URL targetURL       connection    HttpURLConnection  url openConnection        connection setRequestMethod  POST        connection setRequestProperty  Content-Type             application x-www-form-urlencoded         connection setRequestProperty  Content-Length            Integer toString urlParameters getBytes   length        connection setRequestProperty  Content-Language    en-US           connection setUseCaches false       connection setDoOutput true          Send request     DataOutputStream wr   new DataOutputStream           connection getOutputStream         wr writeBytes urlParameters       wr close           Get Response       InputStream is   connection getInputStream        BufferedReader rd   new BufferedReader new InputStreamReader is        StringBuilder response   new StringBuilder       or StringBuffer if Java version 5      String line      while   line   rd readLine       null          response append line         response append   r              rd close        return response toString        catch  Exception e        e printStackTrace        return null      finally       if  connection    null          connection disconnect

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Apache HttpComponents  The examples for the two modules - HttpCore and HttpClient will get you started right away   Not that HttpUrlConnection is a bad choice  HttpComponents will abstract a lot of the tedious coding away  I would recommend this  if you really want to support a lot of HTTP servers clients with minimum code  By the way  HttpCore could be used for applications  clients or servers  with minimum functionality  whereas HttpClient is to be used for clients that require support for multiple authentication schemes  cookie support etc

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From Oracle s java tutorial  import java net    import java io     public class URLConnectionReader       public static void main String   args  throws Exception           URL yahoo   new URL  http   www yahoo com             URLConnection yc   yahoo openConnection            BufferedReader in   new BufferedReader                                  new InputStreamReader                                  yc getInputStream              String inputLine           while   inputLine   in readLine       null               System out println inputLine           in close

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You may use Socket for this like  String host    www yourhost com   Socket socket   new Socket host  80   String request    GET   HTTP 1 0 r n r n   OutputStream os   socket getOutputStream    os write request getBytes     os flush     InputStream is   socket getInputStream    int ch  while   ch is read      -1      System out print  char ch   socket close

[java] How to send HTTP request in java?

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