Handling file upload in a non-blocking manner
- by Kaliyug Antagonist
The background thread is here
Just to make objective clear - the user will upload a large file and must be redirected immediately to another page for proceeding different operations. But the file being large, will take time to be read from the controller's InputStream. So I unwillingly decided to fork a new Thread to handle this I/O. The code is as follows :
The controller servlet
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
System.out.println("In Controller.doPost(...)");
TempModel tempModel = new TempModel();
tempModel.uploadSegYFile(request, response);
System.out.println("Forwarding to Accepted.jsp");
/*try {
Thread.sleep(1000 * 60);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}*/
request.getRequestDispatcher("/jsp/Accepted.jsp").forward(request,
response);
}
The model class
package com.model;
import java.io.IOException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.utils.ProcessUtils;
public class TempModel {
public void uploadSegYFile(HttpServletRequest request,
HttpServletResponse response) {
// TODO Auto-generated method stub
System.out.println("In TempModel.uploadSegYFile(...)");
/*
* Trigger the upload/processing code in a thread, return immediately
* and notify when the thread completes
*/
try {
FileUploaderRunnable fileUploadRunnable = new FileUploaderRunnable(
request.getInputStream());
/*
* Future<FileUploaderRunnable> future = ProcessUtils.submitTask(
* fileUploadRunnable, fileUploadRunnable);
*
* FileUploaderRunnable processed = future.get();
*
* System.out.println("Is file uploaded : " +
* processed.isFileUploaded());
*/
Thread uploadThread = new Thread(fileUploadRunnable);
uploadThread.start();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} /*
* catch (InterruptedException e) { // TODO Auto-generated catch block
* e.printStackTrace(); } catch (ExecutionException e) { // TODO
* Auto-generated catch block e.printStackTrace(); }
*/
System.out.println("Returning from TempModel.uploadSegYFile(...)");
}
}
The Runnable
package com.model;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.ByteBuffer;
import java.nio.channels.Channels;
import java.nio.channels.ReadableByteChannel;
public class FileUploaderRunnable implements Runnable {
private boolean isFileUploaded = false;
private InputStream inputStream = null;
public FileUploaderRunnable(InputStream inputStream) {
// TODO Auto-generated constructor stub
this.inputStream = inputStream;
}
public void run() {
// TODO Auto-generated method stub
/* Read from InputStream. If success, set isFileUploaded = true */
System.out.println("Starting upload in a thread");
File outputFile = new File("D:/06c01_output.seg");/*
* This will be changed
* later
*/
FileOutputStream fos;
ReadableByteChannel readable = Channels.newChannel(inputStream);
ByteBuffer buffer = ByteBuffer.allocate(1000000);
try {
fos = new FileOutputStream(outputFile);
while (readable.read(buffer) != -1) {
fos.write(buffer.array());
buffer.clear();
}
fos.flush();
fos.close();
readable.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("File upload thread completed");
}
public boolean isFileUploaded() {
return isFileUploaded;
}
}
My queries/doubts :
Spawning threads manually from the Servlet makes sense to me logically but scares me coding wise - the container isn't aware of these threads after all(I think so!)
The current code is giving an Exception which is quite obvious - the stream is inaccessible as the doPost(...) method returns before the run() method completes :
In Controller.doPost(...)
In TempModel.uploadSegYFile(...)
Returning from TempModel.uploadSegYFile(...)
Forwarding to Accepted.jsp
Starting upload in a thread
Exception in thread "Thread-4" java.lang.NullPointerException
at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:512)
at org.apache.coyote.http11.InternalInputBuffer.fill(InternalInputBuffer.java:497)
at org.apache.coyote.http11.InternalInputBuffer$InputStreamInputBuffer.doRead(InternalInputBuffer.java:559)
at org.apache.coyote.http11.AbstractInputBuffer.doRead(AbstractInputBuffer.java:324)
at org.apache.coyote.Request.doRead(Request.java:422)
at org.apache.catalina.connector.InputBuffer.realReadBytes(InputBuffer.java:287)
at org.apache.tomcat.util.buf.ByteChunk.substract(ByteChunk.java:407)
at org.apache.catalina.connector.InputBuffer.read(InputBuffer.java:310)
at org.apache.catalina.connector.CoyoteInputStream.read(CoyoteInputStream.java:202)
at java.nio.channels.Channels$ReadableByteChannelImpl.read(Unknown Source)
at com.model.FileUploaderRunnable.run(FileUploaderRunnable.java:39)
at java.lang.Thread.run(Unknown Source)
Keeping in mind the point 1., does the use of Executor framework help me in anyway ?
package com.utils;
import java.util.concurrent.Future;
import java.util.concurrent.ScheduledThreadPoolExecutor;
public final class ProcessUtils {
/* Ensure that no more than 2 uploads,processing req. are allowed */
private static final ScheduledThreadPoolExecutor threadPoolExec = new ScheduledThreadPoolExecutor(
2);
public static <T> Future<T> submitTask(Runnable task, T result) {
return threadPoolExec.submit(task, result);
}
}
So how should I ensure that the user doesn't block and the stream remains accessible so that the (uploaded)file can be read from it?
