This was an interesting problem. The key thing is to write your own appender. I looked up the in built org.apache.log4j.ConsoleAppender code for inspiration. I have tested this in my tomcat and verified that it works. I used log4j-1.2.17 (hopefully shouldn't matter)
1) First implement your own appender. This appender will write all log events to current thread's outputstream
package com.tstwbprj.log;
import org.apache.log4j.Layout;
import org.apache.log4j.WriterAppender;
import java.io.IOException;
import java.io.OutputStream;
public class HttpLogAppender extends WriterAppender {
static ThreadLocal<OutputStream> streamPerHttpThread = new ThreadLocal<OutputStream>();
public HttpLogAppender() {
}
public HttpLogAppender(Layout layout) {
setLayout(layout); //super-class method
activateOptions();
}
public void setCurrentHttpStream(OutputStream stream) {
streamPerHttpThread.set(stream);
}
public void activateOptions() {
setWriter(createWriter(new CurrentHttpThreadOutStream()));
}
/**
* An implementation of OutputStream that redirects to the
* current http threads servlet output stream
*/
private static class CurrentHttpThreadOutStream extends OutputStream {
public CurrentHttpThreadOutStream() {
}
public void close() {
}
public void flush() throws IOException {
OutputStream stream = streamPerHttpThread.get();
if (stream != null) {
stream.flush();
}
}
public void write(final byte[] b) throws IOException {
OutputStream stream = streamPerHttpThread.get();
if (stream != null) {
stream.write(b);
}
}
public void write(final byte[] b, final int off, final int len)
throws IOException {
OutputStream stream = streamPerHttpThread.get();
if (stream != null) {
stream.write(b, off, len);
}
}
public void write(final int b) throws IOException {
OutputStream stream = streamPerHttpThread.get();
if (stream != null) {
stream.write(b);
}
}
}
}
2) Add this appender in your log4j configuration file just like the other settings
log4j.rootLogger=DEBUG, CA, FA , HA
..
log4j.appender.HA=com.tstwbprj.log.HttpLogAppender
log4j.appender.HA.layout=org.apache.log4j.PatternLayout
log4j.appender.HA.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n
3) Add a small piece of code in your servlet so that this appender works correctly . Here's my servlet.
import org.apache.log4j.Category;
import org.apache.log4j.Logger;
import javax.servlet.ServletOutputStream;
import java.io.IOException;
public class LogServlet extends javax.servlet.http.HttpServlet {
private static final Logger LOG = Logger.getLogger(LogServlet.class);
protected void doPost(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) throws javax.servlet.ServletException, IOException {
}
protected void doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) throws javax.servlet.ServletException, IOException {
ServletOutputStream outstream = response.getOutputStream();
configureLogForCurrentRequest(outstream);
LOG.info("Got request");//this is now send to the servlet output stream !!
LOG.info("Hello!!");
LOG.info("Done!!");
}
private void configureLogForCurrentRequest(ServletOutputStream outstream) {
HttpLogAppender appender = (HttpLogAppender) LOG.getAppender("HA");
while (appender == null) {
Category parent = LOG.getParent();
if (parent == null) {
break; //This ideally shouldn't happen. Navigated all the way to root logger and still did not find appender !!..something wrong with log4j configuration setup
}
appender = (HttpLogAppender) parent.getAppender("HA");
}
appender.setCurrentHttpStream(outstream);
}
}
Caution : This is not thoroughly tested especially with multiple servlet requests etc. Also not sure why you want to do this. Its not typical to pipe log messages to browser. Proceed with caution..:)-
worker.work()run in same or other thread? Problem suggests that it runs in another thread. – Davide