calling servlet from java program and more

[Vijaishanker bala]

Hi,
Is it possible to call a servlet from a java program.
The application is as follows,
1.I get a list(an ArrayList) of search results from a web service to a java program.
2.In this java program, i perform some functions on the obtained list.
3.In the next step, the List of results need to be passed on to a servlet, from the java program(this is where i need some help).
Being specific on my query, I would like to pass an arrayList of objects to a servlet from a java program.Can some one please tell me, how this can be done.

Thanks

Vijai
[ June 19, 2006: Message edited by: Bear Bibeault ]

[William Brogden]

The simplest thing to do would be to serialize the ArrayList to a File that is placed where the servlet can read it as required. This would be possible if:
1. all objects in the ArrayList are Serializable
2. your application and the servlet have access to the same disk directory somehow

If these conditions do not hold then things get more complicated.
Bill

[Vijaishanker bala]

Thanks William for your reply.From what u replied,instead of serializing it to a file, I think I will serialize the List to a Binary Output Stream and send it to the servlet using the java.net api and at the servlet side, deserialize it and use it there.I guess that shouldnt be a problem with the sandbox security required in creating a file and serializing to it.
Thanks again

Vijai

[Carl Trusiak]

You don't need to serialize it to a file. Look at the code for ObjectServlet and HTTP for and example in the Code Barn

[Harpreet Hira]

This thread discusses similar problem

[Darren Edwards]

This may not apply as I do not know the full details of your environment, but do you really need to pass to a servlet? Perhaps it is more appropiate for a servlet to do all the work (assuming it is a process started by a user and a web browser) or maybe you only require use of libraries that the servlet has?

[Vijaishanker bala]

Thanks for the help everyone. My code is as follows...
This is the part which calls the servlet.

/**
 * @param args
 */
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
// List results;
// BasicQueryEngine qEngine = new BasicQueryEngine(
// "D:/programming/dump/indexes/dump2_index",
// "D:/programming/dump/indexes/dump2_index/index.xml");
// results = qEngine.Query("U411736", "all");
URL aURL = new URL(
"http://localhost:8080/ematrix/generateBusinessObjects.do");
URLConnection aConnection = aURL.openConnection();
aConnection.setDoInput(true);
aConnection.setDoOutput(true);
aConnection.setUseCaches(false);
aConnection.setDefaultUseCaches(false);
aConnection.setRequestProperty("Content-Type",
"application/octet-stream");
List aList = new ArrayList();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
aList.add("6");
aList.add("7");
aList.add("8");
aList.add("9");
aList.add("10");
ObjectOutputStream out = new ObjectOutputStream(aConnection
.getOutputStream());
out.writeObject(aList);
out.flush();
out.close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
    

And this is the servlet code which takes the result.

 
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
 
ObjectInputStream resultStream = null;
List results = null;
try {
resultStream = new ObjectInputStream(request.getInputStream());
results = (List) resultStream.readObject();
resultStream.close();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
   

But the problem right now is, I dont know if the servlet is being called and if any exception has occured. How can I test if the servlet is being called, i.e. like writing something to a file or something else.

Thanks again

Vijai

[Saritha Penumudi]

You can give log statements after each step.
Also, catch Excpetion along with other exceptions.

Just curious to know about the requirement. What servlet will do after it get results back from your java program.

Looks like this the back ground process that runs and returns results to UI. Are you updating UI dynamically based on the results?
[ June 19, 2006: Message edited by: Saritha ventrapragada ]

[Vijaishanker bala]

Hi,
Thanks to everyone...I finally managed to make the java code communicate with the servlet work..Thanx Carl, that link was extremely useful and Harpreet Hira... thanks to ur link to a similar post, I managed to pick up some useful pointers....and Darren, my application requirements should I decide to accept it, is to connect to an already active session and get a User Context(which I can access only with servlet API),hence I needed to bridge the java code and the session part of the application.
Thanks

Vijai

and herewith I am posting the code that worked should it help someone else


The code that calls the servlet and passes an object(an ArrayList) to it.

/**
 * @param args
 */
public static void main(String[] args) {
// TODO Auto-generated method stub
try {
URL aURL = new URL("http://localhost:8080/ematrix/generateBusinessObjects.do");
URLConnection aConnection = aURL.openConnection();
aConnection.setDoInput(true);
aConnection.setDoOutput(true);
aConnection.setUseCaches(false);
aConnection.setDefaultUseCaches(false);
aConnection.setRequestProperty("Content-Type",
"application/octet-stream");
List aList = new ArrayList();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
aList.add("6");
aList.add("7");
aList.add("8");
aList.add("9");
ObjectOutputStream out = new ObjectOutputStream(aConnection
.getOutputStream());
out.writeObject(aList);
out.flush();
out.close();
ObjectInputStream in = new ObjectInputStream(aConnection
.getInputStream());
String text = (String) in.readObject();
System.out.println(text);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}    

The servlet's doPost that reads the object, in this case an ArrayList and sends the size of the ArrayList back to the java code that called it

 public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ObjectInputStream resultStream = null;
ObjectOutputStream sendStream = null;
List results = null;
try {
resultStream = new ObjectInputStream(request.getInputStream());
results = (List) resultStream.readObject();
resultStream.close();
sendStream = new ObjectOutputStream(response.getOutputStream());
sendStream.writeObject(String.valueOf(results.size()));
sendStream.flush();
sendStream.close();
} catch (IOException e) {
e.printStackTrace(); 
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}   

[Vijaishanker bala]

To Saritha: read your post late, The servlet takes up a list of results, for example, search results, and based upon a few other parameters, creates a JSP that is supposed to vary depending upon other dependent parameters

Vijai

[Bindu Sanju]

Hi Vijaishankar,

I write the colde like this , I am getting exception, please help me.


--------sender file ---------------

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintWriter;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.Servlet;
import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* @version 1.0
* @author
*/
public class URLSender extends HttpServlet implements Servlet {


public void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {


try {

ArrayList aList = new ArrayList();
aList.add("1");
aList.add("2");
aList.add("3");
aList.add("4");
aList.add("5");
aList.add("6");
aList.add("7");
aList.add("8");
aList.add("9");

URL aURL = new URL("http://localhost:9080/GUTA/URLReceiver");
System.out.println("URL : "+aURL);
URLConnection aConnection = aURL.openConnection();
System.out.println("URL COnnection : "+aConnection);
aConnection.setDoInput(true);
aConnection.setDoOutput(true);
aConnection.setUseCaches(false);
aConnection.setDefaultUseCaches(false);
aConnection.setRequestProperty("Content-Type",
"application/octet-stream");

ObjectOutputStream out = new ObjectOutputStream(aConnection
.getOutputStream());
out.writeObject(aList);
out.flush();
out.close();
System.out.println("End of the file");
ObjectInputStream in = new ObjectInputStream(aConnection.getInputStream());
String text = (String) in.readObject();
System.out.println(text);
} catch (Exception e) {
e.printStackTrace();
}
}

}



-----------receiver file in different application---------

import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OptionalDataException;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.URL;
import java.net.URLConnection;
import java.util.List;

import javax.servlet.Servlet;
import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
* @version 1.0
* @author
*/
public class URLReceiver extends HttpServlet implements Servlet {


public void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
resp.setContentType("text/html");
PrintWriter out=resp.getWriter();
out.println("Hi this is Receiver URL");
System.out.println("Hi this is Receiver URL");

ObjectInputStream resultStream = null;
ObjectOutputStream sendStream = null;
List results = null;
try {
resultStream = new ObjectInputStream(req.getInputStream());
results = (List) resultStream.readObject();
resultStream.close();
sendStream = new ObjectOutputStream(resp.getOutputStream());
//sendStream.writeObject(String.valueOf(results.size()));
System.out.println("Hi this is Receiver Size "+String.valueOf(results.size()));
sendStream.flush();
sendStream.close();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}



/*try {

resp.setContentType("text/html");
PrintWriter out=resp.getWriter();
out.println("Hi this is Receiver URL");
System.out.println("Hi this is Receiver URL");















//URL userloginservlet = new URL("http://localhost:9080/DEN/URLSender");
//System.out.println("URL : "+userloginservlet);
//URLConnection servletConnection = userloginservlet.openConnection();
//ObjectOutputStream oos = new ObjectOutputStream(servletConnection.getOutputStream());
ObjectInputStream ois = new ObjectInputStream(req.getInputStream());
DataBean p = (DataBean) ois.readObject();
while(true){

System.out.println("Name Value is : "+p.getName());
System.out.println("Pass Value is : "+p.getPass());
}


//DataBean db=new DataBean();
//db.setName("Yandra");
//db.setPass("ramsea");
//oos.writeObject(db);

//ObjectInputStream ois = new ObjectInputStream(servletConnection.getInputStream());
////outs = servletConnection.getOutputStream();
//DataBean db;
//db = (DataBean) ois.readObject();
//db.setName("Yandra");
//db.setPass("ramsea");
//System.out.println("URL COnnection : "+servletConnection);





} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
*/



}

}


---------exception-------------------

[4/17/07 15:42:54:000 CDT] 60e0c639 WebGroup E SRVE0026E: [Servlet Error]-[URLReceiver]: java.lang.IllegalStateException: Writer already obtained
at com.ibm.ws.webcontainer.srt.SRTServletResponse.getOutputStream(SRTServletResponse.java:490)
at URLReceiver.service(URLReceiver.java:41)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at com.ibm.ws.webcontainer.servlet.StrictServletInstance.doService(StrictServletInstance.java:110)
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet._service(StrictLifecycleServlet.java:174)
at com.ibm.ws.webcontainer.servlet.IdleServletState.service(StrictLifecycleServlet.java:313)
at com.ibm.ws.webcontainer.servlet.StrictLifecycleServlet.service(StrictLifecycleServlet.java:116)
at com.ibm.ws.webcontainer.servlet.ServletInstance.service(ServletInstance.java:283)
at com.ibm.ws.webcontainer.servlet.ValidServletReferenceState.dispatch(ValidServletReferenceState.java:42)
at com.ibm.ws.webcontainer.servlet.ServletInstanceReference.dispatch(ServletInstanceReference.java:40)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.handleWebAppDispatch(WebAppRequestDispatcher.java:948)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.dispatch(WebAppRequestDispatcher.java:530)
at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:176)
at com.ibm.ws.webcontainer.srt.WebAppInvoker.doForward(WebAppInvoker.java:79)
at com.ibm.ws.webcontainer.srt.WebAppInvoker.handleInvocationHook(WebAppInvoker.java:201)
at com.ibm.ws.webcontainer.cache.invocation.CachedInvocation.handleInvocation(CachedInvocation.java:71)
at com.ibm.ws.webcontainer.srp.ServletRequestProcessor.dispatchByURI(ServletRequestProcessor.java:182)
at com.ibm.ws.webcontainer.oselistener.OSEListenerDispatcher.service(OSEListener.java:334)
at com.ibm.ws.webcontainer.http.HttpConnection.handleRequest(HttpConnection.java:56)
at com.ibm.ws.http.HttpConnection.readAndHandleRequest(HttpConnection.java:610)
at com.ibm.ws.http.HttpConnection.run(HttpConnection.java:431)
at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:593)

[NageshPilla]

delete Printwriter out=resp.getWriter(); from URLReciever Servlet.

[Anil K Battu]

I did the same implementation..Control is NOT coming to the other servlet, to read the object.
please help me in this regard