如何将log4j输出重定向到我的HttpServletResponse输出流？

Question

我在JBoss AS 7.1.1.Final上部署的Spring 3.1.1.RELEASE应用程序中使用log4j 1.2.15.我正在尝试将log4j中写入的输出路由到我的响应输出流.我有这样写的输出

private static final Logger LOG = Logger.getLogger(TrainingSessionServiceImpl.class);
…
LOG.info("Creating/updating training session associated with order #:" + order.getId());

我正试图将它路由到我的输出流,如此...

@RequestMapping(value = "/refreshPd", method = RequestMethod.GET)
public void refreshPD(final HttpServletResponse response) throws IOException
{
    ...        
    final WriterAppender appender = new WriterAppender(new PatternLayout("%d{ISO8601} %p - %m%n"),response.getWriter());
    appender.setName("CONSOLE_APPENDER");
    appender.setThreshold(org.apache.log4j.Level.DEBUG);
    Logger.getRootLogger().addAppender(appender);

    worker.work();

    Logger.getRootLogger().removeAppender("CONSOLE_APPENDER");

但遗憾的是,即使我知道(通过调试)日志语句被调用,也没有任何东西输出到我的浏览器.有谁知道如何调整我的设置以使其工作？下面是我的log4j.properties文件,部署到我的wAR的WEB-INF/classes目录.

log4j.rootLogger=DEBUG, CA, FA

#Console Appender
log4j.appender.CA=org.apache.log4j.ConsoleAppender
log4j.appender.CA.layout=org.apache.log4j.PatternLayout
log4j.appender.CA.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

#File Appender
log4j.appender.FA=org.apache.log4j.FileAppender
log4j.appender.FA.File=/usr/java/jboss/server/default/log/log4j.log
log4j.appender.FA.layout=org.apache.log4j.PatternLayout
log4j.appender.FA.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n

# Set the logger level of File Appender to WARN
log4j.appender.FA.Threshold = DEBUG

谢谢, - 戴夫

Answer 1

这是一个有趣的问题. 关键是要编写自己的appender.我查看了内置的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的工作原理.我用log4j-1.2.17(希望无所谓)

1)首先实现自己的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)将此appender添加到log4j配置文件中,就像其他设置一样

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)在servlet中添加一小段代码,以便此appender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);
    }
}

警告:这没有经过彻底的测试,特别是对于多个servlet请求等.也不确定为什么要这样做.将日志消息传递给浏览器并不常见.谨慎行事.. :) -