java debug JPDA (JavaTM Platform Debugger Architecture)

Java 是在 VM 里面运行的语言, 同时要做到平台无关性, 所以它有自己的 debug 接口和实现.
官方关于 JPDA 的链接: https://docs.oracle.com/javase/6/docs/technotes/guides/jpda/
jpda.png

上面的图很容易理解, VM 具体实现和 backend 接口直接使用 JVM TI 来作为通信接口.
Debugger 和 Debuggee 之间定义了协议: JDWP (这类似于 HTTP).
Debugger 自己的和后端通信以及自己的 UI 使用 JDI(这类似与 HTML)

如何远程 debug:
从 Java 9 开始:

java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=127.0.0.1:8000 myApp
java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=*:8000 myApp

Java 9 之前:

java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=8000 OurApplication

Java 5 之前:

java -Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=8000 myApp

参数列表:
a list of options:

  1. transport is the only fully required option. It defines which transport mechanism to use. dt_shmem only works on Windows and if both processes run on the same machine while dt_socket is compatible with all platforms and allows the processes to run on different machines

  2. server is not a mandatory option. This flag, when on, defines the way it attaches to the debugger. It either exposes the process through the address defined in the address option. Otherwise, JDWP exposes a default one

  3. suspend defines whether the JVM should suspend and wait for a debugger to attach or not

  4. address is the option containing the address, generally a port, exposed by the debuggee. It can also represent an address translated as a string of characters (like javadebug if we use server=y without providing an address on Windows)

客户端最简陋的可以使用 jdk 自带 jdb.
更多信息参考: https://www.baeldung.com/java-application-remote-debugging

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