Java ProcessBuilder调试器Netbeans

Question

I am having trouble with the deeper layers of the JVM and its debugging functionality. What I am trying to do is start a separate java program using ProcessBuilder and let it communicate with my main process. All works fine unless I add the command

"-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=1044",

to the ProcessBuilder.

Class toExecute = ExampleSimulationController.class;
String javaHome = System.getProperty("java.home");
String javaBin = javaHome
        + File.separator + "bin"
        + File.separator + "java";
String classpath = System.getProperty("java.class.path");
String className = toExecute.getCanonicalName();

ProcessBuilder builder = new ProcessBuilder(javaBin, "-cp",
        "-agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=1044",
         classpath, className);
builder.redirectErrorStream(true);

In adding this line to the ProcessBuilder (with the intention to add debugging functionality to the subprocess as described, for example, here: What are Java command line options to set to allow JVM to be remotely debugged? I get an exception when trying to read as follows:

BufferedReader mainProcessConsoleOutput = new BufferedReader(new InputStreamReader(mainSimulation.getInputStream()));

and further down:

if(!(line = mainProcessConsoleOutput.readLine()).equals("someText"))

The exception is as follows:

Main Process: Exception in thread "main" java.lang.NoClassDefFoundError: /Users/...[path].../build/classes
Main Process: Caused by: java.lang.ClassNotFoundException: .Users.[same_Path].build.classes
Main Process:   at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
Main Process:   at java.security.AccessController.doPrivileged(Native Method)
Main Process:   at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
Main Process:   at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
Main Process:   at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
Main Process:   at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
Exception in thread "main" java.lang.NullPointerException
at [PacketStructure].SimulationController.main(SimulationController.java:66)

I am using Netbeans as IDE and know about "Attaching a Debugger" and giving it the same port as specified in the command I pass to the ProcessBuilder. However, I don't know when I have to do this - before I specify a breakpoint in the subprocess? Afterwards? So far I did not find any indication that my subprocess is communicating with a debugger in any way.

What seems suspicious to me as well is the fact that the exception is thrown when I try to read from subprocess' stream - and not someplace earlier.

I do use ObjectInputStream and ObjectOutputStream to pass serialized data from one process to the other, but since I cannot debug the subprocess I don't know if that is a potential source of the problem.

I use MacOs.

Since the solution of this problem lies beyond my knowledge of the Java Magic, please help me in solving this riddle.

Thanks,

M

Answer 1

After a lot of time spent trying to solve the problem I finally did:

ProcessBuilder builder = new ProcessBuilder(javaBin,"-agentlib:jdwp=transport=dt_socket,address=localhost:8000,server=n,suspend=y","-cp", classpath, className);

By adding the "-cp" command after the "-agentlib" command apparently the classpath is matched correctly with the className.

Should I have known that the order in which commands are passed is important?

Thx

Answer 2

classpath值必须紧随classpath参数之后。