远程调试Java程序

java 可以以调试模式启动，启动后可以使用 jdb 对程序进行调试。以调试模式启动，需要加入以下参数：

java -Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n

一般如 tomcat, jboss, weblogic 等服务器中会使用 JAVA_OPTS 环境变量，如果要运行这类服务，可以设置该环境变量如下：

linux 下

export JAVA_OPTS="$JAVA_OPTS -Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n"
JAVA_OPTS="$JAVA_OPTS -Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n"

windows 下

set JAVA_OPTS=%JAVA_OPTS% -Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n

maven 使用 MAVEN_OPTS 参数，设置跟上面的类同

以下是一个简单的服务器端代码，接收 UDP 请求

package mm;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UServer {

  public static void main(String[] args) throws IOException {
    DatagramSocket socket = new DatagramSocket(8000);
    while (true) {
      DatagramPacket dataPackage = new DatagramPacket(new byte[100], 100);
      socket.receive(dataPackage);
      System.out.println("Receive from : "
          + dataPackage.getAddress().getHostName());
      System.out.println("Data: [" + new String(dataPackage.getData()) + "]");
      dataPackage.setData("abc你好".getBytes());
      socket.send(dataPackage);
    }
  }

}

通过以下命令运行该服务器：

java -Xdebug -Xrunjdwp:transport=dt_socket,address=8787,server=y,suspend=n mm.UServer

通过以下命运运行 jdb，即可进行调试

[root@server test] # jdb -attach 192.168.1.79:8787 -sourcepath .
Set uncaught java.lang.Throwable
Set deferred uncaught java.lang.Throwable
Initializing jdb ...
> stop at mm.UServer:12
Set breakpoint mm.UServer:12
>
Breakpoint hit: "thread=main", mm.UServer.main(), line=12 bci=11
12          DatagramPacket dataPackage = new DatagramPacket(new byte[100], 100);

main[1] next

Step completed: "thread=main", mm.UServer.main(), line=13 bci=25
13          socket.receive(dataPackage);

main[1] main[1] next
> next
Nothing suspended.
>
Step completed: "thread=main", mm.UServer.main(), line=14 bci=30
14          System.out.println("Receive from : "

main[1] !!
next

Step completed: "thread=main", mm.UServer.main(), line=15 bci=42
15              + dataPackage.getAddress().getHostName());

main[1] main[1] !!
next
>
Step completed: "thread=main", mm.UServer.main(), line=14 bci=55
14          System.out.println("Receive from : "

main[1] !!
next
>
Step completed: "thread=main", mm.UServer.main(), line=16 bci=58
16          System.out.println("Data: [" + new String(dataPackage.getData()) + "]");

main[1] !!
next
>
Step completed: "thread=main", mm.UServer.main(), line=17 bci=95
17          dataPackage.setData("abc你好".getBytes());

main[1] !!
next
>
Step completed: "thread=main", mm.UServer.main(), line=18 bci=104
18          socket.send(dataPackage);

main[1] !!
next
>
Step completed: "thread=main", mm.UServer.main(), line=11 bci=109
11        while (true) {

main[1] !!
next
>
Step completed:
Breakpoint hit: "thread=main", mm.UServer.main(), line=12 bci=11
12          DatagramPacket dataPackage = new DatagramPacket(new byte[100], 100);

main[1]

调试的主要命令有

• stop at 在指定行设置断点
• stop on 在指定的方法设置断点
• next 单步执行到下一步
• !! 重复最后一次命令

目前 eclipse 中已经集成了 jdb，可以在 eclipse 的 debug 选项中设置连接远程主机进行远程调试