-agentlib和-Xdebug区别

http://www.cnblogs.com/lailailai/p/4560399.html

写服务端程序，在开发环境下打开远程调试还是非常有用的，还原现场非常容易，让请求方再发个请求即可。如果下来本地调试的话很多环境与管理服务的地址配置什么的都可能不一样，增加了可变因素。

在需要启动服务调试的jvm启动参数中加入（注意：参数要排在启动类名的前面）

-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=1234

dt_socket：使用的通信方式

server：是主动连接调试器还是作为服务器等待调试器连接

suspend：是否在启动JVM时就暂停，并等待调试器连接

address：地址和端口，地址可以省略，两者用冒号分隔

根据文档和stackoverflow上的讨论，JVM 1.5以后的版本应该使用类似下面的命令（老的还是可以使用的）：

-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=1234

就是一个agentlib就行了，后面的参数都没有变，如果用intellij的远程调试配置的话，它会默认给出这两种参数，让你放到服务器的JVM参数里。

下面摘抄一下官方文档：

-Xdebug

-Xdebugenables debugging capabilities in the JVM which are used by the Java Virtual Machine Tools Interface (JVMTI). JVMTI is a low-level debugging interface used by debuggers and profiling tools. With it, you can inspect the state and control the execution of applications running in the JVM.

The subset of JVMTI that is most typically used by profilers is always available. However, the functionality used by debuggers to be able to step through the code and set breakpoints has some overhead associated with it and is not always available. To enable this functionality you must use the-Xdebugoption.

WARNING:

When running with -Xdebug the JVM is not running at its full speed. Thus, the option should not be used for applications when running in production environments.

Operation

Format:-Xdebug

Include this option at startup.

For Example:

java-Xdebug-Xrunjdwp:transport=dt_socket,server=y,suspend=nmyApp

-Xrunjdwp

This option loads the JPDA reference implementation of JDWP. This library resides in the target VM and uses JVMDI and JNI to interact with it. It uses a transport and the JDWP protocol to communicate with a separate debugger application.

Operation

Format:-Xrunjdwp:<name1>[=<value1>],<name2>[=<value2>]...

The-Xrunjdwpoption can be further qualified by specifying one of the sub-options listed inTable2-8.

Table 2-8 -Xrunjdwp Sub-options

Name	Required?	Default Value	Description
help	no	N/A	Prints a brief help message and exits the VM.
transport	yes	none	Name of the transport to use in connecting to debugger application.
server	no	“n”	If “y”, listen for a debugger application to attach; otherwise, attach to the debugger application at the specified address. If “y” and no address is specified, choose atransport addressat which to listen for a debugger application, and print the address to the standard output stream.
address	yes, ifserver=n no, otherwise	““	Transport addressfor the connection. If server=n, attempt to attach to debugger application at this address. If server=y, listen for a connection at this address.
launch	no	none	At completion of JDWP initialization, launch the process given in this string. This option is used in combination with onthrow and/or onuncaught to provide “Just-In-Time debugging” in which a debugger process is launched when a particular event occurs in this VM. Note that the launched process is not started in its own window. In most cases the launched process should be a small application which in turns launches the debugger application in its own window. The following strings are appended to the string given in this argument (space-delimited). They can aid the launched debugger in establishing a connection with this VM. The resulting string is executed. The value of thetransportsub-option. The value of theaddresssub-option (or the generated address if one is not given)
onthrow	no	none	Delay initialization of the JDWP library until an exception of the given class is thrown in this VM. The exception class name must be package-qualified.Connection establishment is included in JDWP initialization, so it will not begin until the exception is thrown.
onuncaught	no	“n”	If “y”, delay initialization of the JDWP library until an uncaught exception is thrown in this VM. Connection establishment is included in JDWP initialization, so it will not begin until the exception is thrown. See the JDI specification for com.sun.jdi.ExceptionEvent for a definition of uncaught exceptions.
stdalloc	no	“n”	By default, the JDWP reference implementation uses an alternate allocator for its memory allocation. If “y”, the standard C runtime library allocator will be used. This option is mainly for testing; use it with care. Deadlocks can occur in this VM if the alternative allocator is disabled.
strict	no	“n”	If “y”, assume strict JVMDI conformance. This will disable all workarounds to known bugs in JVMDI implementations. This option is mainly for testing and should be used with care.
suspend	no	“y”	If “y”, VMStartEvent has a suspend Policy of SUSPEND_ALL. If “n”, VMStartEvent has a suspend policy of SUSPEND_NONE.

For example:

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

This command:

• Listens for a socket connection on port 8000.
• Suspends this VM before main class loads (suspend=yby default).
• Once the debugger application connects, it can send a JDWP command to resume the VM.

-Xrunjdwp:transport=dt_shmem,server=y,suspend=n 

This command:

• Chooses an available shared memory transport address and print it tostdout.
• Listens for a shared memory connection at that address.
• Allows the VM to begin executing before the debugger application attaches.

-Xrunjdwp:transport=dt_socket,address=myhost:8000 

This command:

• Attaches to a running debugger application via socket on host myhost at port 8000.
• Suspends this VM before main class loads.

-Xrunjdwp:transport=dt_shmem,address=mysharedmemory 

This command:

• Attaches to a running debugger application via shared memory at transport addressmysharedmemory.
• Suspends this VM before main class loads.

-Xrunjdwp:transport=dt_socket,server=y,address=8000,onthrow=java.io.IOException,launch=/usr/local/bin/debugstub 

This command:

• Waits for an instance ofjava.io.IOExceptionto be thrown in this VM.
• Suspends the VM (suspend=yby default).
• Listens for a socket connection on port 8000.
• Executes the following:

/usr/local/bin/debugstub dt_socket myhost:8000

This program can launch a debugger process in a separate window which will attach to this VM and begin debugging it.

-Xrunjdwp:transport=dt_shmem,server=y,onuncaught=y,launch=d:\bin\debugstub.exe 

This command:

• Waits for an uncaught exception to be thrown in this VM.
• Suspends the VM.
• Selects a shared memory transport address and listen for a connection at that address.
• Executes the following:

d:\bin\debugstub.exe dt_shmem <address>
where<address>is the selected shared memory address.

This program can launch a debugger process in a separate window which will attach to this VM and begin debugging it.

另外一篇文档（JPDA Connection and Invocation Details）：

Sun VM Invocation Options

This section describes the options necessary to invoke Sun VMs for debugging.

Sun's VM implementations require command line options to load the JDWP agent for debugging. From 5.0 onwards the-agentlib:jdwpoption is used to load and specify options to the JDWP agent. For releases prior to 5.0, the-Xdebugand-Xrunjdwpoptions are used (the 5.0 implementation also supports the-Xdebugand-Xrunjdwpoptions but the newer-agentlib:jdwpoption is preferable as the JDWP agent in 5.0 uses the JVM TI interface to the VM rather than the older JVMDI interface).

If your debugger application uses the JDISun Command Line Launching Connector, the connector will use the-Xdebugand-Xrunjdwpoptions as the Connector may be used to connect to a pre-5.0 target VM.

If the target VM is 5.0 or newer the-agentlib:jdwpoption is specified as follows:

-agentlib:jdwp=<sub-options>

Loads the JPDA reference implementation of JDWP. This library resides in the target VM and uses JVM TI and JNI to interact with it. It uses a transport and the JDWP protocol to communicate with a separate debugger application. Specific sub-options are describedbelow.

For releases prior to 5.0 the-Xdebugand-Xrunjdwpoptions are used:

-Xdebug

Enables debugging

-Xrunjdwp:<sub-options>

Loads the JPDA reference implementation of JDWP. This library resides in the target VM and uses JVMDI and JNI to interact with it. It uses a transport and the JDWP protocol to communicate with a separate debugger application. Specific sub-options are describedbelow.

-agentlib:jdwp and -Xrunjdwp sub-options

The -agentlib:jdwp and -Xrunjdwp option can be further qualified with sub-options. The sub-options are specified as follows:

-agentlib:jdwp=<name1>[=<value1>],<name2>[=<value2>]...

or

-Xrunjdwp:<name1>[=<value1>],<name2>[=<value2>]...

The table below describes the options that can be used:

-Xrunjdwp Sub-options namerequired?default valuedescription

help	no	N/A	Prints a brief help message and exits the VM.
transport	yes	none	Name of the transport to use in connecting to debugger application.
server	no	"n"	If "y", listen for a debugger application to attach; otherwise, attach to the debugger application at the specifiedaddress. If "y" and no address is specified, choose atransport addressat which to listen for a debugger application, and print the address to the standard output stream.
address	yes, ifserver=n no, otherwise	""	Transport addressfor the connection. If server=n, attempt to attach to debugger application at this address. If server=y, listen for a connection at this address.
timeout	no	""	If server=y specifies the timeout, in milliseconds, to wait for the debugger to attach. If server=n specifies the timeout, in milliseconds, to use when attaching to the debugger. Note that the timeout option may be ignored by some transport implementations.
launch	no	none	At completion of JDWP initialization, launch the process given in this string. This option is used in combination withonthrowand/oronuncaughtto provide "Just-In-Time debugging" in which a debugger process is launched when a particular event occurs in this VM. Note that the launched process is not started in its own window. In most cases the launched process should be a small application which in turns launches the debugger application in its own window. The following strings are appended to the string given in this argument (space-delimited). They can aid the launched debugger in establishing a connection with this VM. The resulting string is executed. The value of thetransportsub-option. The value of theaddresssub-option (or the generated address if one is not given)
onthrow	no	none	Delay initialization of the JDWP library until an exception of the given class is thrown in this VM. The exception class name must be package-qualified.Connection establishment is included in JDWP initialization, so it will not begin until the exception is thrown.
onuncaught	no	"n"	If "y", delay initialization of the JDWP library until an uncaught exception is thrown in this VM. Connection establishment is included in JDWP initialization, so it will not begin until the exception is thrown. See the JDI specification for com.sun.jdi.ExceptionEvent for a definition of uncaught exceptions.
suspend	no	"y"	If "y", VMStartEvent has a suspendPolicy of SUSPEND_ALL. If "n", VMStartEvent has a suspendPolicy of SUSPEND_NONE.

Examples

-agentlib:jdwp=transport=dt_socket,server=y,address=8000

Listen for a socket connection on port 8000. Suspend this VM before main class loads (suspend=y by default). Once the debugger application connects, it can send a JDWP command to resume the VM.

-agentlib:jdwp=transport=dt_socket,server=y,address=localhost:8000,timeout=5000

Listen for a socket connection on port 8000 on the loopback address only. Terminate if the debugger does not attach within 5 seconds. Suspend this VM before main class loads (suspend=y by default). Once the debugger application connects, it can send a JDWP command to resume the VM.

-agentlib:jdwp=transport=dt_shmem,server=y,suspend=n

Choose an available shared memory transport address and print it to stdout. Listen for a shared memory connection at that address. Allow the VM to begin executing before the debugger application attaches.

-agentlib:jdwp=transport=dt_socket,address=myhost:8000

Attach to a running debugger application via socket on host myhost at port 8000. Suspend this VM before the main class loads.

-agentlib:jdwp=transport=dt_shmem,address=mysharedmemory

Attach to a running debugger application via shared memory at transport address "mysharedmemory". Suspend this VM before the main class loads.

-agentlib:jdwp=transport=dt_socket,server=y,address=8000,onthrow=java.io.IOException,launch=/usr/local/bin/debugstub

Wait for an instance of java.io.IOException to be thrown in this VM. Suspend the VM (suspend=y by default). Listen for a socket connection on port 8000. Execute the following: "/usr/local/bin/debugstub dt_socket myhost:8000".This program can launch a debugger process in a separate window which will attach to this VM and begin debugging it.

-agentlib:jdwp=transport=dt_shmem,server=y,onuncaught=y,launch=d:\bin\debugstub.exe

Wait for an uncaught exception to be thrown in this VM. Suspend the VM. Select a shared memory transport address and listen for a connection at that address. Execute the following: "d:\bin\debugstub.exe dt_shmem <address>", where<address>is the selected shared memory address. This program can launch a debugger process in a separate window which will attach to this VM and begin debugging it.