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Invoking Salesforce REST based web service from Java

This post will explain the approach to call the Salesfore REST based webservice through java.
I have exposed a Apex class as REST service from salesforce to fetch the account details.

@RestResource(urlMapping='/AccountDetails/*')
global with sharing class AccountDetails {

    @HttpGet
    global static Account doGet() {
        RestRequest req = RestContext.request;
        RestResponse res = RestContext.response;
        String accountId = req.requestURI.substring(req.requestURI.lastIndexOf('/')+1);
        System.debug('Account Id:'+accountId);
        Account result = [SELECT Id, Name, Phone, Website FROM Account WHERE Id = :accountId];
        return result;
    }
}
The communication is of two steps

•  getting the access_token 
•  invoking the service endpoint by attaching the access_token to the request.

To obtain an access token, we will send an HTTP POST request to the authentication endpoint exposed by Salesforce - https://login.salesforce.com/services/oauth2/token  with the details client_id, client_secret, username and password.This values can be get from the configured Connected Apps from salesforce.




import java.io.*;
import java.net.*;
import org.w3c.dom.*;

public class RestCaller {
public static void main(String[] args) throws Exception {

String urlParameters = "grant_type=password&client_id=3MVG9Y6d_xxxxxxxx&client_secret=80xxxxxxxx&username=albinsharpxxxxx&password=xxxxxxxxx";

String loginresponse = RestCaller.execute(
"https://login.salesforce.com/services/oauth2/token", "POST",urlParameters, "application/x-www-form-urlencoded", null);
String sessionId=getSessionId(loginresponse);
String serviceResponse =RestCaller.execute("https://ap1.salesforce.com/services/apexrest/AccountDetails","GET","0019000000AZBCNAA5","application/xml",sessionId);
System.out.println("Service Response \n" + serviceResponse);
}

public static String execute(String targetURL, String HttpMethod,
String urlParameters, String contentType, String SessionId) {
URL url;
HttpURLConnection connection = null;
try {
url = new URL(targetURL);
if (HttpMethod == "GET") {
url = new URL(url.toString() + "/" + urlParameters);
}
connection = (HttpURLConnection) url.openConnection();
if (SessionId != null)
connection.setRequestProperty("Authorization", "OAuth "+ SessionId);
connection.setRequestProperty("accept", "application/xml");
if (HttpMethod == "POST") {
connection.setRequestMethod("POST");
connection.setRequestProperty("Content-Length","" + Integer.toString(urlParameters.getBytes().length));
connection.setRequestProperty("Content-Type", contentType);
connection.setRequestProperty("Content-Language", "en-US");
connection.setUseCaches(false);
connection.setDoInput(true);
connection.setDoOutput(true);
OutputStream os = connection.getOutputStream();
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(os, "UTF-8"));
writer.write(urlParameters);
writer.flush();
writer.close();
os.close();
}

InputStream is = connection.getInputStream();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
String line;
StringBuffer response = new StringBuffer();
while ((line = rd.readLine()) != null) {
response.append(line);
response.append('\r');
}
rd.close();
return response.toString();
} catch (Exception e) {
e.printStackTrace();
return (e.getClass().getName());
}

finally {
if (connection != null) {
connection.disconnect();
}
}

}

static String getSessionId(String loingResponse)
{
   java.io.InputStream sbis = new java.io.StringBufferInputStream(loingResponse.toString());
       javax.xml.parsers.DocumentBuilderFactory b = javax.xml.parsers.DocumentBuilderFactory.newInstance();
       b.setNamespaceAware(false);
       org.w3c.dom.Document doc = null;
       javax.xml.parsers.DocumentBuilder db = null;
       try {
           db = b.newDocumentBuilder();
           doc = db.parse(sbis);
       } catch (Exception e) {
           e.printStackTrace();
       }  
       org.w3c.dom.Element element = doc.getDocumentElement();
       String access_token="";
       NodeList nodeList = element.getElementsByTagName("access_token");
       if(nodeList!=null && nodeList.getLength() > 0){
        Element myElement = (Element)nodeList.item(0);
        access_token= myElement.getFirstChild().getNodeValue();
       }
       return access_token;
}
}
O/P
<?xml version="1.0" encoding="UTF-8"?>
<response xsi:type="sObject" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<type>Account</type>
<Id>0019000000AZBCNAA5</Id>
<Name>GenePoint</Name>
<Phone>(650) 867-3450</Phone>
<Website>www.genepoint.com</Website>
</response>