REST Webservices in Java

Preparing and Executing a simple REST Webservice using Tomcat and MyEclipse:

1) Create a new WebService Project and name it "RestWebService2".
2) Create a package "model" and create a java file "HelloWorldService.java". This is basically your webservice. 
Contents are shown below.
3) Add some contents into "WEB-INF/web.xml", contents are shown below.
4) Add a new "sun-jaxws.xml" file inside "WEB-INF/" directory.
5) Run your application in Tomcat. In MyEclipse it is in-built, so just right click on project and Choose
"Run as"--> Server application (then choose Tomcat). It will show the browser with Index.jsp (default JSP
page contents in browser).
6) How to hit URL and what you will get as output is also mentioned at the end.
7) This is a basic example, once you run successfully, you can read further in other sites.
8) This is a tested example, works fine for me.

//HelloWorldService.java
package model;
import javax.annotation.Resource;

import java.io.ByteArrayInputStream;

import javax.xml.transform.Source;
import javax.xml.transform.stream.StreamSource;

import javax.xml.ws.BindingType;
import javax.xml.ws.Provider;
import javax.xml.ws.WebServiceContext;
import javax.xml.ws.WebServiceProvider;
import javax.xml.ws.handler.MessageContext;
import javax.xml.ws.http.HTTPBinding;
import javax.xml.ws.http.HTTPException;

@WebServiceProvider
@BindingType(value=HTTPBinding.HTTP_BINDING)
public class HelloWorldService implements Provider<Source> {

@Resource(type=Object.class)
protected WebServiceContext context;

public Source invoke(Source source) {
try {
MessageContext mc = context.getMessageContext();

String queryString = (String)mc.get(MessageContext.QUERY_STRING);
String pathInfo = (String)mc.get(MessageContext.PATH_INFO);

if (queryString != null && queryString.contains("name=")) {
return sayHello(queryString);
} else if (pathInfo != null && pathInfo.contains("/name")) {
return sayHello(pathInfo);
} else {
return sayHello("Unknown");
}
} catch(Exception e) {
e.printStackTrace();
throw new HTTPException(500);
}
}

private Source sayHello(String name) {
Source source = new StreamSource(
new ByteArrayInputStream((new String("<result>Hello Client, Response from Rest Webservice : "+name+"</result>")).getBytes()));
return source;
}
}

//web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

<listener>
<listener-class>
com.sun.xml.ws.transport.http.servlet.WSServletContextListener
</listener-class>
</listener>
<servlet>
<servlet-name>helloWorld</servlet-name>
<servlet-class>
com.sun.xml.ws.transport.http.servlet.WSServlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>helloWorld</servlet-name>
<url-pattern>/hello/*</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>


//sun-jaxws.xml
<?xml version="1.0" encoding="UTF-8"?>

<endpoints xmlns="http://java.sun.com/xml/ns/jax-ws/ri/runtime"
version="2.0">
<endpoint name="helloWorld" implementation="model.HelloWorldService"
url-pattern="/hello/*" />
</endpoints>

//index.jsp
It can have anything here.... no use....



URL Hit:
http://10.200.101.156:8080/RestWebService2/hello?name=deepakKumarmodi
Output:
<result>Hello Client, Response from Rest Webservice : name=deepakKumarmodi</result> 


URL Hit:
http://10.200.101.156:8080/RestWebService2/hello/name/deepakKumarmodi
Output:
<result>Hello Client, Response from Rest Webservice : /name/deepakKumarmodi</result> 


URL Hit (Any other non matching pattern):
http://10.200.101.156:8080/RestWebService2/hello
Output:
<result>Hello Client, Response from Rest Webservice : Unknown</result> 


-----------------------END-------------------------------

Web services in Java using Apache Axis2

Dear Reader,

WebService is basically an application which allows communication between two software components. 
It means both the software components(client and server here) should understand a common language format, then 
only they can talk to each other. 

So, the basic Web services platform is XML + HTTP. All the standard Web Services works using following components:
    a. SOAP (Simple Object Access Protocol)
    b. UDDI (Universal Description, Discovery and Integration)
    c. WSDL (Web Services Description Language)

We are discussing here the point c. WSDL is nothing but an XML File only. So if you want to talk to a web service, 
that service must be in the form of *.wsdl. Each service has some operations. Operations are actual methods which 
are available for communication (in Java terminology: Service is a program, Operations are methods).

NOTE: In WebServices your request and response both will be of XML type and hence it must comply with SCHEMA or DTD.

Now let us see the working example from scratch. I am explaining how to create a web service and how to invoke it in 
a very simple manner in Windows OS. This is done using Apache Axis2 server.

You need:
1) Axis2 server, download it from below link and extract it in "C:\" drive. I have renamed the folder as "axis2-1.5-bin".
http://apache.ziply.com//axis/axis2/java/core/1.5.6/axis2-1.5.6-bin.zip

2) Go to "C:\axis2-1.5-bin\bin" directory. Then type "axis2server.bat", you will see:-
C:\axis2-1.5\bin>axis2server.bat
    Using JAVA_HOME C:\Program Files\Java\jdk1.5.0_13
    Using AXIS2_HOME C:\axis2-1.5
    [INFO] [SimpleAxisServer] Starting
    [INFO] [SimpleAxisServer] Using the Axis2 RepositoryC:\axis2-1.5\repository
    [SimpleAxisServer] Using the Axis2 RepositoryC:\axis2-1.5\repository
    [SimpleAxisServer] Using the Axis2 Configuration FileC:\axis2-1.5\conf\axis2.xml
    [INFO] Clustering has been disabled
    [INFO] Deploying module: addressing-1.5 - file:/C:/axis2-1.5/repository/modules/addressing-1.5.mar
    [INFO] Deploying module: metadataExchange-1.5 - file:/C:/axis2-1.5/repository/modules/mex-1.5.mar
    [INFO] Deploying module: mtompolicy-1.5 - file:/C:/axis2-1.5/repository/modules/mtompolicy-1.5.mar
    [INFO] Deploying module: ping-1.5 - file:/C:/axis2-1.5/repository/modules/ping-1.5.mar
    [INFO] Deploying module: script-1.5 - file:/C:/axis2-1.5/repository/modules/scripting-1.5.mar
    [INFO] Deploying module: soapmonitor-1.5 - file:/C:/axis2-1.5/repository/modules/soapmonitor-1.5.mar
    [INFO] Deploying module: metadataExchange-1.5 - file:/C:/axis2-1.5/lib/mex-1.5.jar
    [INFO] Deploying Web service: ArithmeticService.aar - file:/C:/axis2-1.5/repository/services/ArithmeticService.aar
    [INFO] Deploying Web service: AsynchronousService.aar - file:/C:/axis2-1.5/repository/services/AsynchronousService.aar
    [INFO] Deploying Web service: version.aar - file:/C:/axis2-1.5/repository/services/version.aar
    [INFO] Deploying Web service: WeatherService.aar - file:/C:/axis2-1.5/repository/services/WeatherService.aar
    [INFO] Listening on port 8080
    [INFO] [SimpleAxisServer] Started
    [SimpleAxisServer] Started
//This shows your server is started, now you have to create application and deploy.

3) Now open one more command prompt, go to "C:\axis2-1.5\repository\services" directory. 
This services directory is having list of all web services deployed as *.aar files. These *.aar files are actully
like JAR/WAR/EAR files which Apache Axis treats as "Apache Archive". Axis2 supports hot deployment, means
create *.aar file and paste to this directory, If server is already running, your web service will be deployed.

4) Now let us write a Java program. Create a directory anywhere in hard disk, assume "D:\axis2_example_dmodi\dmodi\". You will 
write Java code (Web service at Server side) here. This will be your service:-

//HelloWorldService.java
package dmodi;
public class HelloWorldService {
    public String sayHello(String name) {
        return "Hello, I am server.." + name;
    }

    public String sum(String n1, String n2) {
        int num = Integer.parseInt(n1) +Integer.parseInt(n2);
        return "The summation:" + num;
    }
    public String sub(String n1, String n2) {
        int num = Integer.parseInt(n1) -Integer.parseInt(n2);
        return "The substraction:" + num;
    }
    public String div(String n1, String n2) {
        int num = Integer.parseInt(n1) / Integer.parseInt(n2);
        return "The division:" + num;
    }
    public String mul(String n1, String n2) {
        int num = Integer.parseInt(n1) * Integer.parseInt(n2);
        return "The multiple:" + num;
    }
}

//Create "META-INF" folder inside "D:\axis2_example_dmodi\" and then write below code and save it as "services.xml" file and save 
//inside "META-INF". 
//services.xml: 
<?xml version="1.0" encoding="UTF-8"?>
<service name="HelloService">
    <parameter name="ServiceClass">dmodi.HelloWorldService</parameter>
    <operation name="sum">
        <messageReceiver
            class="org.apache.axis2.rpc.receivers.RPCMessageReceiver" />
    </operation>
    <operation name="sayHello">
        <messageReceiver
            class="org.apache.axis2.rpc.receivers.RPCMessageReceiver" />
    </operation>
    <operation name="mul">
        <messageReceiver
            class="org.apache.axis2.rpc.receivers.RPCMessageReceiver" />
    </operation>
    <operation name="sub">
        <messageReceiver
            class="org.apache.axis2.rpc.receivers.RPCMessageReceiver" />
    </operation>
     
    <operation name="div">
        <messageReceiver
            class="org.apache.axis2.rpc.receivers.RPCMessageReceiver" />
    </operation>
</service>

=======================================================================
That's it. Now you have to compile the Java code and create *.aar File as below:
Compilation of java code:
D:\axis2_example_dmodi\dmodi>javac HelloWorldService.java
D:\axis2_example_dmodi\dmodi>cd ..

//Creating Service file(.aar):-
D:\axis2_example_dmodi>jar -cvf HelloService.aar META-INF\services.xml dmodi\HelloWorldService.class
added manifest
adding: META-INF/services.xml(in = 895) (out= 212)(deflated 76%)
adding: dmodi/HelloWorldService.class(in = 1056) (out= 497)(deflated 52%)

---HelloService.aar created.

Now drop this HelloService.aar into "C:\axis2-1.5-bin\repository\services" folder. It will be automatically deployed 
if server is running else start the server (Command: C:\axis2-1.5\bin>axis2server.bat).

//Open browser and type:- http://localhost:8080/axis2/services/HelloService?wsdl
//localhost: can be replaced with IP address of your system. After hitting above URL, you will see the HelloService.wsdl file.
Wow, your first web service at server side is ready now.
===================================================================================================

Now since your web service is ready, you have to write a Java client to invoke it, pass some request and get the output.
After all this is what we need to do else what is the use of doing all these stuffs :-).

Writing Client:
Writing client is as simple, you just need a Java file, dependent JARs and run the Java (Client) code.
Supporting JARs are already available in the "lib" directory which comes with downloaded Apache Axis2.
For me it is in "C:\Axis2-1.5.6\lib". Here I have written Java code in Eclipse where setting classpath is too easy.
Just add all the JARs from "C:\Axis2-1.5.6\lib" directory for setting classpath in "Java Build Path" in eclipse. 
However if you don't want to add all the jar files, then below jar files are for you (check the image below):
















//Client code: ArithmeticClient.java
import javax.xml.namespace.QName;
import org.apache.axiom.om.OMElement;
import org.apache.axis2.AxisFault;
import org.apache.axis2.addressing.EndpointReference;
import org.apache.axis2.client.Options;
import org.apache.axis2.rpc.client.RPCServiceClient;
public class ArithmeticClient {
    public static void main(String[] args1) throws AxisFault {
        RPCServiceClient serviceClient = new RPCServiceClient();
        Options options = serviceClient.getOptions();
        EndpointReference targetEPR = new EndpointReference("http://localhost:8080/axis2/services/HelloService?wsdl");
        options.setTo(targetEPR);

        QName opSum = new QName("http://dmodi", "sum");  //http://dmodi is the namespace, you can see while hitting WSDL.
        Object[] opSumArgs = new Object[] { 14,7 };                    
        serviceClient.invokeRobust(opSum, opSumArgs);
        OMElement response = serviceClient.invokeBlocking(opSum, opSumArgs);
        System.out.println("Sum Called:"+response);
        
        opSum = new QName("http://dmodi", "mul");
        opSumArgs = new Object[] { 14,7 };
        serviceClient.invokeRobust(opSum, opSumArgs);
        response = serviceClient.invokeBlocking(opSum, opSumArgs);
        System.out.println("Multiple Called:"+response);
        
        opSum = new QName("http://dmodi", "sub");
        opSumArgs = new Object[] { 14,7 };
        serviceClient.invokeRobust(opSum, opSumArgs);
        response = serviceClient.invokeBlocking(opSum, opSumArgs);
        System.out.println("Substraction Called:"+response);
        
        opSum = new QName("http://dmodi", "div");
        opSumArgs = new Object[] { 14,7 };
        serviceClient.invokeRobust(opSum, opSumArgs);
        response = serviceClient.invokeBlocking(opSum, opSumArgs);
        System.out.println("Division Called:"+response);
    }
}
//Compile and Run this. Output is given below:
--------------------------------------------------------
Sum Called:<ns:sumResponse xmlns:ns="http://dmodi"><ns:return>The summation:21</ns:return></ns:sumResponse>
Multiple Called:<ns:mulResponse xmlns:ns="http://dmodi"><ns:return>The multiple:98</ns:return></ns:mulResponse>
Substraction Called:<ns:subResponse xmlns:ns="http://dmodi"><ns:return>The substraction:7</ns:return></ns:subResponse>
Division Called:<ns:divResponse xmlns:ns="http://dmodi"><ns:return>The division:2</ns:return></ns:divResponse>
--------------------------------------------------------
You see, Client is passing parameter (14, 7). Web service is returning the data after doing operations in XML format.
Now you need to parse the response XML to get the exact data.


--------------------------------------------------------
Some more stuffs:
Web service invocation by client can be done in two ways:
1) Synchronous invocation:  Client will be waiting to get the response after submitting request.
2) Asynchronous invocation: Client will send the request and will not wait for response.

The above example was showing Synchronous communication.
One more example is given below (Synchronous itself) where we are defining our own NAMESPACE.
//QuoteService.java  (WebService for Server side)
import java.util.HashMap;
import org.apache.axiom.om.OMAbstractFactory;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMFactory;
import org.apache.axiom.om.OMNamespace;
public class QuoteService {
    private HashMap map=null;
    public OMElement sayQuote(OMElement in){
        HashMap map=new HashMap();
        map.put("Numbers","0 to 9");
        map.put("Letters","A-Z and a-z");
        map.put("Name","Deepak Kumar Modi");
        String name=in.getText();
        String info=(String)map.get(name);
        OMFactory fac=OMAbstractFactory.getOMFactory();
        OMNamespace omNs=fac.createOMNamespace("http://www.deepakmodi2006.blogspot.com/","deepak");
        OMElement resp=fac.createOMElement("sayResponse",omNs);
        resp.setText(info);
        return resp;
    }
}

//services.xml
<?xml version="1.0" encoding="UTF-8"?>
<service name="QuoteService">
    <description>
        This is a sample Web Service, designed by Deepak.Modi.
    </description>
    <parameter name="ServiceClass" locked="false">
        QuoteService
    </parameter>
    <operation name="sayQuote">
        <messageReceiver
            class="org.apache.axis2.receivers.RawXMLINOutMessageReceiver" />
    </operation>
</service>

//build.xml to create *.aar file
<?xml version="1.0" encoding="UTF-8"?>
<project name="Deepak kumar Modi" default="main" basedir=".">
    <property name="src.dir" value="src" />
    <property name="classes.dir" value="classes" />
    <property name="lib.dir" value="C:\Axis2-1.5.6\lib" />
    
    <path id="project.classpath">    
    <fileset dir="${lib.dir}">
    <include name="**/*.jar" />
    </fileset>        
    </path>
    
    <target name="clean">
        <delete dir="${classes.dir}" />
        <delete file="QuoteService.aar"/>
    </target>

    <target name="prepare" depends="clean">
        <mkdir dir="${classes.dir}" />
    </target>

    <target name="compile" depends="prepare">
        <javac srcdir="${src.dir}" destdir="${classes.dir}" classpathref="project.classpath" />
    </target>

    <target name="main" depends="compile" >
        <copydir  src="META-INF"   dest="${classes.dir}/META-INF">
        </copydir>
            
        <jar jarfile="QuoteService.aar" basedir="${classes.dir}"/>    
        <echo message="Main target completed.." />
    </target>
</project>

//Create QuoteService.aar and deploy at the axis2 services directory.

//TestClient.java
import org.apache.axiom.om.OMAbstractFactory;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMFactory;
import org.apache.axiom.om.OMNamespace;
import org.apache.axis2.addressing.EndpointReference;
import org.apache.axis2.client.Options;
import org.apache.axis2.client.ServiceClient;
public class TestClient {
    private static EndpointReference targetEPR=new EndpointReference("http://localhost:8080/axis2/services/QuoteService?wsdl");
    public static OMElement getSayHelloOMElement(){
        OMFactory fac=OMAbstractFactory.getOMFactory();
        OMNamespace omNs=fac.createOMNamespace("http://www.deepakmodi2006.blogspot.com/","deepak");
        OMElement method=fac.createOMElement("sayQuote",omNs);
        method.setText("Numbers");
        System.out.println(method);
        return method;
    }
    public static void main(String[] args){
        try{
            Options options=new Options();
            options.setTo(targetEPR);
            ServiceClient sender=new ServiceClient();
            sender.setOptions(options);
            OMElement sayQuote=TestClient.getSayHelloOMElement();
            OMElement result=sender.sendReceive(sayQuote);
            System.out.println(result);
        }catch(Exception axisFault){
            axisFault.printStackTrace();
        }
    }
}
//Output:
------------------------------------------------
<deepak:sayQuote xmlns:deepak="http://www.deepakmodi2006.blogspot.com/">Numbers</deepak:sayQuote>
<deepak:sayResponse xmlns:deepak="http://www.deepakmodi2006.blogspot.com/">0 to 9</deepak:sayResponse>
------------------------------------------------END------------------------------------------------

WebService invocation in Java using Axis2 (Async)

Web services using Asynchronous communication
Dear reader,
Web services can be invoked by two ways:
1) Synchronous communication, here client will be waiting till it gets the response from web service. This
    is called sequence execution of web service.
2) Asynchronous communication, here client will not wait for response from web service, once it sends the 
    request. This is like a parallel execution (calling web service and doing its own task).

How to work with Web service and Synchronous Communication is already discussed in my another blog in link
"http://deepakmodi2006.blogspot.com/2009/08/web-service-in-java-using-axis2.html". 
This is for Asynchronous communication. I am writing only client code here as web service at 
Server side will be same, only Client execution needs to be changed. Please see the below link for 
Web service deployed at Server.

//Writing 
import org.apache.axiom.om.OMAbstractFactory;
import org.apache.axiom.om.OMElement;
import org.apache.axiom.om.OMFactory;
import org.apache.axiom.om.OMNamespace;
import org.apache.axis2.addressing.EndpointReference;
import org.apache.axis2.client.Options;
import org.apache.axis2.client.ServiceClient;
import org.apache.axis2.client.async.AsyncResult;
import org.apache.axis2.client.async.Callback;
public class ArithmeticAsyncClient {
    private static EndpointReference targetEPR=new EndpointReference
    ("http://10.200.101.137:8080/axis2/services/QuoteService?wsdl");
    public static OMElement getSayHelloOMElement(){
        OMFactory fac=OMAbstractFactory.getOMFactory();
        OMNamespace omNs=fac.createOMNamespace("http://www.deepakmodi2006.blogspot.com/","deepak");
        OMElement method=fac.createOMElement("sayQuote",omNs);
        method.setText("Numbers");
        System.out.println(method);
        return method;
    }
    public static void main(String[] args){
        try{
            Options options=new Options();
            options.setTo(targetEPR);
            ServiceClient sender=new ServiceClient();
            sender.setOptions(options);
            OMElement sayQuote=TestClient.getSayHelloOMElement();
            
            Callback callback2 = new Callback() {
                public void onComplete(AsyncResult result) {
                    String responseString = result.getResponseEnvelope().toString();
                    System.out.println("Got response :"+responseString);
                }
                public void onError(Exception e) {
                    e.printStackTrace();
                }
            };

            sender.sendReceiveNonBlocking(sayQuote,callback2);
            System.out.println("Asynchronous web service already invoked...");

            while(!callback2.isComplete()) {
                Thread.sleep(100);
                System.out.println("Thread is waiting to get the response");
                //This block will keep executing till the response comes.
            }
        }catch(Exception axisFault){
            axisFault.printStackTrace();
        }
    }
}    
//Output:
log4j:WARN No appenders could be found for logger (org.apache.axis2.util.Loader).
log4j:WARN Please initialize the log4j system properly.
<deepak:sayQuote xmlns:deepak="http://www.deepakmodi2006.blogspot.com/">Numbers</deepak:sayQuote>
Asynchronous web service already invoked...
Thread is waiting to get the response
Thread is waiting to get the response
Thread is waiting to get the response
Got response :
  <?xml version='1.0' encoding='utf-8'?>
    <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
     <soapenv:Body>
       <deepak:sayResponse xmlns:deepak="http://www.deepakmodi2006.blogspot.com/">0 to 9</deepak:sayResponse>
     </soapenv:Body>
  </soapenv:Envelope>
Thread is waiting to get the response
---------------------------------------------------------
//The containts "Got response :" and then XML contents come in single line in output, just to show reader,
I have broken this in line.
==========================================END==============================