这是一个有趣的问题。 关键是编写自己的 appender。我查找了内置的 org.apache.log4j.ConsoleAppender 代码以获取灵感。我已经在我的 tomcat 中对此进行了测试并验证了它是否有效。我使用了 log4j-1.2.17（希望没关系）
1）首先实现你自己的appender。此 appender 会将所有日志事件写入当前线程的输出流
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) 在你的 log4j 配置文件中添加这个 appender，就像其他设置一样
log4j.rootLogger=调试，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) 在您的 servlet 中添加一小段代码，以便此附加程序正常工作。这是我的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);
}
}
注意：这没有经过彻底测试，特别是对于多个 servlet 请求等。也不确定为什么要这样做。将日志消息通过管道传输到浏览器并不典型。谨慎行事.. :)-