The where threadindex command dumps the stack of the specified thread. The where all command dumps the stack of all threads in the current thread group. The where command with no arguments dumps the stack of the current thread. The thread is specified with the thread index described in the threads command. Many jdb commands are based on the setting of the current thread. Select a thread to be the current thread. In this example, the thread index is 4, the thread is an instance of, the thread name is main, and it is currently running. For each thread, its name and current status are printed and an index that can be used in other commands. List the threads that are currently running. The dump command supports the same set of expressions as the print command. For objects, the dump command prints the current value of each field defined in the object. Print new ("Hello").length()įor primitive values, the dump command is identical to the print command. Print myObj.myMethod() (if myMethod returns a non-null) Print i + j + k (i, j, k are primities and either fields or local variables) The print command supports many simple Java expressions including those with method invocations, for example: Note: To display local variables, the containing class must have been compiled with the javac -g option.
JDB STRUGGLE SESSION HOW TO
See the dump command to find out how to get more information about an object. For objects, a short description is printed. For variables or fields of primitive types, the actual value is printed. printĭisplays Java objects and primitive values. contĬontinues execution of the debugged application after a breakpoint, exception, or step. The run command is available only when the jdb command starts the debugged application as opposed to attaching to an existing JVM.
runĪfter you start JDB and set breakpoints, you can use the run command to execute the debugged application. The help or ? commands display the list of recognized commands with a brief description. The JDB supports other commands that you can list with the -help option. The following is a list of the basic jdb commands. The Java Platform Debugger Architecture has additional documentation on these connection options. There are many other ways to connect the debugger to a JVM, and all of them are supported by the jdb command. The M圜lass argument is not specified in the jdb command line in this case because the jdb command is connecting to an existing JVM instead of launching a new JVM. You can then attach the jdb command to the JVM with the following command: Java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n M圜lass This loads in-process debugging libraries and specifies the kind of connection to be made. Syntax for starting a JVM to which the jdb command attaches when the JVM is running is as follows.
When started this way, the jdb command calls a second JVM with the specified parameters, loads the specified class, and stops the JVM before executing that class's first instruction.Īnother way to use the jdb command is by attaching it to a JVM that is already running. For example, if your application's main class is M圜lass, then use the following command to debug it under JDB: Do this by substituting the jdb command for the java command in the command line. The most frequently used way is to have JDB launch a new JVM with the main class of the application to be debugged. Note: Here the TestClass is not added to the JDB command, because JDB is connected to the running VM instead of starting a new one.There are many ways to start a JDB session. You can now attach the JDB to the JVM with the following command: > java -agentlib: jdwp = transport = dt_shmem, address = jdbconn, server = y, suspend = n TestClass Supposethat the main class name is TestClass and JVM allows the JDB to connect it later. agentlib: jdwp = transport = dt_shmem, address =, server = y, suspend = n Example The following syntax is for the JDB session: The syntax and example below is given to sta rt a JDB session in adding the JDB to a running JVM.
Start a session by adding JDB to a running Java virtual machine Then, it loads the class and stops it before executing the first instruction of the class. If you follow this command, it starts a new JVM with all parameters specified. The following command starts a JDB session from TestClass.
Suppose that we have a class named TestClass. The following commandstarts a JDB session for you: Syntax
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