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How To

Sample basic REST client operations in Java

How To posted 10/28/08 by Dave Smith , tagged Web Services API

18883 Views, 1 Comment

Title:

Sample basic REST client operations in Java

Product:

Rally Enterprise

Abstract:

How To:

Attached is a sample Java client that does various REST operations using local files. This client basically reproduces some of the functionality that the curl application has ( http://curl.haxx.se/ ).

You can make things as complicated or as simple as you like, but it boils down to needing to be able to issue various HTTP requests, and being able to interpret XML that comes back.

The basics to think about with REST are that HTTP methods translate to different operations, so:

HTTP PUT == create new object
HTTP GET == read object
HTTP POST == update object
HTTP DELETE == delete object

All objects in REST have a URI. So, every defect in the system has a unique URI. Queries have unique URIs, etc.. If I want to update some defect, I POST an XML document to that defect's URI. If I want to delete a particular defect, I issue an HTTP DELETE request to that URI, etc.

Our web services docs ( https://rally1.rallydev.com/slm/doc/webservice ) explains most of this in pretty good detail (click on the "REST" link on the left).

Code:

package com.rallydev.webservice.rest;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import sun.misc.BASE64Encoder;

public class RESTClient
{
    private static final String GET = "GET";
    private static final String PUT = "PUT";
    private static final String DELETE = "DELETE";
    private static final String POST = "POST";
    
    private RESTClient()
    {
        super();
    }
    
    private static void usage()
    {
        System.out.println("Usage:");
        System.out.println("  For get and delete:");
        System.out.println("    java -jar restclient.jar [-quiet] user pass GET/DELETE url");
        System.out.println("");
        System.out.println("  For put and post, sending the contents of a file as the body:");
        System.out.println("    java -jar restclient.jar [-quiet] user pass PUT/POST url filename");
        System.out.println("");
        System.out.println("  -quiet will cause only the response body to be printed, otherwise");
        System.out.println("  the response headers and timing information is included.");
        System.exit(1);
    }
    
    public static void main(String arguments[])
    {
        List argsList = new ArrayList(arguments.length);
        for (int i=0; i<arguments.length; i++) argsList.add(arguments[i]);
        
        Iterator args = argsList.iterator();
        
        boolean quiet = false;
        if (!args.hasNext()) usage();
        String quietFlag = (String)argsList.iterator().next();
        if ("-quiet".equalsIgnoreCase(quietFlag))
        {
            args.next();
            quiet = true;
        }
        
        if (!args.hasNext()) usage();
        String user = (String)args.next();

        if (!args.hasNext()) usage();
        String pass = (String)args.next();
        
        try
        {
            if (!args.hasNext()) usage();
            String method = (String)args.next();
            
            if (!args.hasNext()) usage();
            URL url = new URL((String)args.next());
            
            if (GET.equalsIgnoreCase(method))
            {
                if (args.hasNext()) usage();
                request(quiet, GET, url, user, pass, null);
            }
            else if (PUT.equalsIgnoreCase(method))
            {
                if (!args.hasNext()) usage();
                String file = (String)args.next();
                request(quiet, PUT, url, user, pass, new FileInputStream(new File(file)));
            }
            else if (POST.equalsIgnoreCase(method))
            {
                if (!args.hasNext()) usage();
                String file = (String)args.next();
                request(quiet, POST, url, user, pass, new FileInputStream(new File(file)));
            }
            else if (DELETE.equalsIgnoreCase(method))
            {
                if (args.hasNext()) usage();
                request(quiet, DELETE, url, user, pass, null);
            }
            else
            {
                usage();
            }
        }
        catch (Exception x)
        {
            System.err.println(x);
            System.exit(1);
        }
    }
    
    private static void request(boolean quiet, String method, URL url, String username, String password, InputStream body)
    throws IOException
    {
        // sigh.  openConnection() doesn't actually open the connection,
        // just gives you a URLConnection.  connect() will open the connection.
        if (!quiet)
        {
            System.out.println("[issuing request: " + method + " " + url + "]");
        }
        HttpURLConnection connection = (HttpURLConnection)url.openConnection();
        connection.setRequestMethod(method);
        
        // write auth header
        BASE64Encoder encoder = new BASE64Encoder();
        String encodedCredential = encoder.encode( (username + ":" + password).getBytes() );
        connection.setRequestProperty("Authorization", "BASIC " + encodedCredential);
        
        // write body if we're doing POST or PUT
        byte buffer[] = new byte[8192];
        int read = 0;
        if (body != null)
        {
            connection.setDoOutput(true);
            
            OutputStream output = connection.getOutputStream();
            while ((read = body.read(buffer)) != -1)
            {
                output.write(buffer, 0, read);
            }
        }
        
        // do request
        long time = System.currentTimeMillis();
        connection.connect();
        
        InputStream responseBodyStream = connection.getInputStream();
        StringBuffer responseBody = new StringBuffer();
        while ((read = responseBodyStream.read(buffer)) != -1)
        {
            responseBody.append(new String(buffer, 0, read));
        }
        connection.disconnect();
        time = System.currentTimeMillis() - time;
        
        // start printing output
        if (!quiet)
            System.out.println("[read " + responseBody.length() + " chars in " + time + "ms]");
        
        // look at headers
        // the 0th header has a null key, and the value is the response line ("HTTP/1.1 200 OK" or whatever)
        if (!quiet)
        {
            String header = null;
            String headerValue = null;
            int index = 0;
            while ((headerValue = connection.getHeaderField(index)) != null)
            {
                header = connection.getHeaderFieldKey(index);
                
                if (header == null)
                    System.out.println(headerValue);
                else
                    System.out.println(header + ": " + headerValue);
                
                index++;
            }
            System.out.println("");
        }
        
        // dump body
        System.out.print(responseBody);
        System.out.flush();
    }
}

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Comments

posted 11/19/08 by Eddie
On updates I was getting the following error using this RESTClient code for a POST (update)

<?xml version="1.0" encoding="UTF-8"?>

<OperationResult rallyAPIMajor="1" rallyAPIMinor="9">

<Errors>

<OperationResultError>Cannot parse input stream as XML document: Error on line -1: Premature end of file.</OperationResultError>

</Errors>

<Warnings />

</OperationResult>

To fix this problem I set the content type to "text/xml" with the following line just after the "Authorization" property is set:

connection.setRequestProperty("Content-Type","text/xml");