Posting Form Data with Java Client using java.net.URL Example

Posting Query Parameters using the URL and HttpURLConnection Class

In this example, we use java.net.URL to POST form data using query parameters to call web service and return results. The example provided is very succinct and describes everything in detail.

The URL class represents and Uniform Resource Locator — an address to a location on the internet to some resource whether it be a web page for your Web browser, a file for FTP or a service to produce or consume some data. The following URL shown below takes you to this post using the http protocol, hosted on www.avaldes.com domain, using port 8080, with this path or reference.

URL Structure

Common components of a URL

Although there can be more components in a URL, the most common form has four components detailed above. Additional components may include query parameters which are separated by a question mark (?) after the Path and each additional query parameter is separated by ampersand (&).

Example using POST Request with Web Service

In this example, we will add a new book using POST method passing all form parameters as query parameters in my Java program. I am building that queryParam object using StringBuffer class and using append for each of the parameters and their corresponding values.

package com.avaldes.tutorial;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class HttpURLPostQueryParamsExample {


  public static void main(String[] args) {
    String URLAddress = "http://localhost:8080/RestfulFormParamExample/rest/books/add";
    String inputString = null;
    int responseCode = 0;
    
    try {
      URL url = new URL(URLAddress); 
      try {
        // Get an HttpURLConnection subclass object instead of URLConnection
        HttpURLConnection myHttpConnection = (HttpURLConnection) url.openConnection();
        
        // ensure you use the GET method
        myHttpConnection.setRequestMethod("POST");
        myHttpConnection.setDoOutput(true);
        
        // create the query params
        StringBuffer queryParam = new StringBuffer();
        queryParam.append("isbn=");
        queryParam.append("123456765");
        queryParam.append("&");
        queryParam.append("name=");
        queryParam.append("RESTful Web Services Made Easy");
        queryParam.append("&");
        queryParam.append("author=");
        queryParam.append("Amaury Valdes");
        queryParam.append("&");
        queryParam.append("publisher=");
        queryParam.append("Packt");
        
        
        // Output the results
        OutputStream output = myHttpConnection.getOutputStream();
        output.write(queryParam.toString().getBytes());
        output.flush();
        
        // get the response-code from the response 
        responseCode = myHttpConnection.getResponseCode();
        
        // print out URL details
        System.out.format("Connecting to %s\nConnection Method: '%s'\nResponse Code is: %d\n", URLAddress, "POST", responseCode);
        System.out.println("----[ URL DETAILS ]-----------------");
        System.out.println("URL Protocol....: " + url.getProtocol());
        System.out.println("URL Host........: " + url.getHost());
        System.out.println("URL Port........: " + url.getPort());
        System.out.println("URL Authority...: " + url.getAuthority());
        System.out.println("URL Path........: " + url.getPath());
        System.out.println("URL User Info...: " + url.getUserInfo());
        System.out.println("URL Query Info..: " + url.getQuery());
        
        System.out.println("----[ OUTPUT BELOW ]-----------------------------------------------------------------");
        
        // open the contents of the URL as an inputStream and print to stdout
        BufferedReader in = new BufferedReader(new InputStreamReader(
            myHttpConnection.getInputStream()));
        while ((inputString = in.readLine()) != null) {
          System.out.println(inputString);
        }
        in.close();   
        System.out.println("-------------------------------------------------------------------------------------");
      } catch (IOException e) {
        e.printStackTrace();
      }
    } catch (MalformedURLException e) {
      e.printStackTrace();
    }
  }
}

Output of RESTful Web Service using POST

Connecting to http://localhost:8080/RestfulFormParamExample/rest/books/add
Connection Method: 'POST'
Response Code is: 200
----[ URL DETAILS ]-----------------
URL Protocol....: http
URL Host........: localhost
URL Port........: 8080
URL Authority...: localhost:8080
URL Path........: /RestfulFormParamExample/rest/books/add
URL User Info...: null
URL Query Info..: null
----[ OUTPUT BELOW ]-----------------------------------------------------------------
addBook: Book [ISBN=123456765, name=RESTful Web Services Made Easy, author=Amaury Valdes, publisher=Packt, stockQty=0, price=0.0]
-------------------------------------------------------------------------------------

RESTful Web services details

I am using the following RESTful web service in my call to to POST form data. For more details on the restful web service itself, please refer to RESTful Web Services @FormParam Example using JAX-RS and Jersey for complete details.

package com.avaldes;

import java.util.ArrayList;
import java.util.List;

import javax.ws.rs.FormParam;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.core.Response;

import org.apache.log4j.Logger;

import com.avaldes.model.Book;

@Path("/books")
public class RestfulFormParamExample {
  static Logger logger = Logger.getLogger(RestfulFormParamExample.class);
  static List<Book> bookList = new ArrayList<Book>(); 
  
  @POST
  @Path("/add")
  @Produces(MediaType.TEXT_HTML)
  public Response addBook(@FormParam("isbn") String ISBN, 
                @FormParam("name") String name,
                @FormParam("author") String author,
                @FormParam("publisher") String publisher,
                @FormParam("stock_qty") int stockQty,
                @FormParam("price") double price) {

    Book b = new Book();
    b.setISBN(ISBN);
    b.setName(name);
    b.setAuthor(author);
    b.setPublisher(publisher);
    b.setStockQty(stockQty);
    b.setPrice(price);
    
    bookList.add(b);
    
    String msg = "addBook: " + b.toString();
    logger.info(msg);
    
    return Response.ok(msg).entity(msg).build();
  }
  
  @POST
  @Path("/map")
  @Produces(MediaType.TEXT_HTML)
  public Response viewMap(MultivaluedMap<String, String> formFields) {

    StringBuffer msg = new StringBuffer(" View all Form Fields:<br/><br/>");
    for (String field : formFields.keySet()) {
      msg.append(field);
      msg.append(" : ");
      msg.append(formFields.get(field));
      msg.append("<br/>");
    }

    return Response.status(200).entity(msg.toString()).build();
  }
  
  @GET
  @Path("/list")
  public Response getBooks() {
    
    String msg = "getBooks: " + bookList;
    logger.info(msg);
    
    return Response.ok(msg).entity(msg).build();
  } 
}

That’s It!

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