I was asked once in an interview How will you check the different status of thread ?

The question was to write a java code which will check which thread is waiting for which lock (if any) or if it dead etc.

Here is one way of doing it….

/**
 * THIS CODE IS DISTRIBUTED "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */
package com.mumz.test.thread.threadinfo;

/**
 * @author prabhat.jha
 */
public class MyOwnThread implements Runnable {
	
	public StringBuilder	builder	= new StringBuilder();
	/**
	 * @param data
	 */
	public void addData(String data) {
		builder.append(isValidString(data) ? data : "");
	}
	
	/**
	 * (non-Javadoc)
	 * 
	 * @see java.lang.Runnable#run()
	 */
	public void run() {
		synchronized (builder) {
			if (builder.toString().length() > 10) {
				try {
					builder.wait();
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
			if (builder.toString().length() > 10) {
				String content = builder.toString().substring(0, 9);
				builder.delete(0, builder.length() - 1);
				builder.append(content);
			}
			if (builder.length() > 10) {
				builder.notifyAll();
			}
		}
	}
	/**
	 * @param string
	 * @return
	 */
	private boolean isValidString(String string) {
		return (string != null && !string.equals("") && string.trim().length() > 0);
	}
}

Lets create thread and then check if they are waiting for lock to be acquired or else just print there status, here is the code snippet:

package com.mumz.test.thread.threadinfo;

/**
 * THIS CODE IS DISTRIBUTED "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 */

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadInfo;
import java.lang.management.ThreadMXBean;

/**
 * @author prabhat.jha
 *
 */
public class ThreadFactory {
	
	public static void main(String[] args) {
		MyOwnThread myOwnThread = null;
		Thread thread = null;
		long[] threadIds = new long[20];
		for (int iDx = 0; iDx < 20; iDx++) {
			myOwnThread = new MyOwnThread();
			myOwnThread.addData("Thread : " + iDx);
			thread = new Thread(myOwnThread);
			thread.setName(String.valueOf(iDx));
			threadIds[iDx] = thread.getId();
			thread.start();
		}
		ThreadFactory factory = new ThreadFactory();
		factory.checkThreadStatus(threadIds);
	}
	
	/**
	 * @param threadIds
	 */
	private void checkThreadStatus(long[] threadIds) {
		ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();
		ThreadInfo[] threadInfos = threadMXBean.getThreadInfo(threadIds);
		StringBuilder info = new StringBuilder();
		for (ThreadInfo threadInfo : threadInfos) {
			if (threadInfo == null) {
				continue;
			}
			info.append("threadInfo.getThreadId() : " + threadInfo.getThreadId());
			info.append("\n");
			info.append("threadInfo.getThreadName() : " + threadInfo.getThreadName());
			info.append("\n");
			info.append("threadInfo.getThreadState() : " + threadInfo.getThreadState());
			info.append("\n");
			info.append("threadInfo.getLockName() : " + threadInfo.getLockName());
			info.append("\n");
			info.append("threadInfo.getLockOwnerId() : " + threadInfo.getLockOwnerId());
			info.append("\n");
			info.append("threadInfo.getLockOwnerName() : " + threadInfo.getLockOwnerName());
		}
		writeDataToFile(info.toString());
	}
	
	/**
	 * @param info
	 */
	private void writeDataToFile(String info) {
		File file = new File("c://" + System.currentTimeMillis());
		PrintWriter pw = null;
		BufferedOutputStream bos = null;
		try {
			if (!file.exists()) {
				file.createNewFile();
			}
			bos = new BufferedOutputStream(new FileOutputStream(file));
			pw = new PrintWriter(bos);
			pw.write(info);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			pw.close();
			try {
				bos.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
}