调试工具

jdk自带的工具

• jmap
• jconsole
• VisualVM

jmap

• jmap -histo:live pid 列出该进程的所有活动实例统计信息
• jmap -dump:live,file=test.map pid 转储到文件
• jmap -J-Xms256m -dump:live,file=test.map pid 指定内存,防止内存不足
• jmap -dump:format=b,file=test.map pid 转储堆快照

C:\>jmap

Usage:

    jmap [option] <pid>

        (to connect to running process)

    jmap [option] <executable <core>

        (to connect to a core file)

    jmap [option] [server_id@]<remote server IP or hostname>

        (to connect to remote debug server)

where <option> is one of:

    <none>               to print same info as Solaris pmap

    -heap                to print java heap summary

    -histo[:live]        to print histogram of java object heap; if the "live"

                         suboption is specified, only count live objects

    -clstats             to print class loader statistics

    -finalizerinfo       to print information on objects awaiting finalization

    -dump:<dump-options> to dump java heap in hprof binary format

                         dump-options:

                           live         dump only live objects; if not specified,

                                        all objects in the heap are dumped.

                           format=b     binary format

                           file=<file>  dump heap to <file>

                         Example: jmap -dump:live,format=b,file=heap.bin <pid>

    -F                   force. Use with -dump:<dump-options> <pid> or -histo

                         to force a heap dump or histogram when <pid> does not

                         respond. The "live" suboption is not supported

                         in this mode.

    -h | -help           to print this help message

    -J<flag>             to pass <flag> directly to the runtime system

mat (Memory Analysis Tool)

• 内存分析工具

jhat (Java Heap Analysis Tool)

• 堆内存分析工具
• jhat test.map 分析堆快照，并生成html文件
• jhat -J-Xmx512m test.map 指定内存,防止内存不足

C:\>jhat

ERROR: No arguments supplied

Usage:  jhat [-stack <bool>] [-refs <bool>] [-port <port>] [-baseline <file>] [-debug <int>] [-version] [-h|-help] <file>

        -J<flag>          Pass <flag> directly to the runtime system. For

                          example, -J-mx512m to use a maximum heap size of 512MB

        -stack false:     Turn off tracking object allocation call stack.

        -refs false:      Turn off tracking of references to objects

        -port <port>:     Set the port for the HTTP server.  Defaults to 7000

        -exclude <file>:  Specify a file that lists data members that should

                          be excluded from the reachableFrom query.

        -baseline <file>: Specify a baseline object dump.  Objects in

                          both heap dumps with the same ID and same class will

                          be marked as not being "new".

        -debug <int>:     Set debug level.

                            0:  No debug output

                            1:  Debug hprof file parsing

                            2:  Debug hprof file parsing, no server

        -version          Report version number

        -h|-help          Print this help and exit

        <file>            The file to read

For a dump file that contains multiple heap dumps,

you may specify which dump in the file

by appending "#<number>" to the file name, i.e. "foo.hprof#3".

All boolean options default to "true"

tips

• jps(Java Virtual Machine Process Status Tool )
• jps命令可以查看当前使用java虚拟机的进程

jstack

jstack可以用来查看Java进程里的线程都在干什么，这通常对于应用没反应，非常慢等等场景都有不小的帮助，jstack默认只能看到Java栈，而jstack -m则可以看到线程的Java栈和native栈，但如果Java方法被编译过，则看不到（然而大部分经常访问的Java方法其实都被编译过）。

C:\>jstack

Usage:

    jstack [-l] <pid>

        (to connect to running process)

    jstack -F [-m] [-l] <pid>

        (to connect to a hung process)

    jstack [-m] [-l] <executable> <core>

        (to connect to a core file)

    jstack [-m] [-l] [server_id@]<remote server IP or hostname>

        (to connect to a remote debug server)

Options:

    -F  to force a thread dump. Use when jstack <pid> does not respond (process is hung)

    -m  to print both java and native frames (mixed mode)

    -l  long listing. Prints additional information about locks

    -h or -help to print this help message

jinfo

可以输出并修改运行时的java进程的opts。用处比较简单，用于输出JAVA系统参数及命令行参数。用法是jinfo -opt pid 如：查看2788的MaxPerm大小可以用 jinfo -flag MaxPermSize 2788

where <option> is one of:

    -flag <name>         to print the value of the named VM flag

    -flag [+|-]<name>    to enable or disable the named VM flag

    -flag <name>=<value> to set the named VM flag to the given value

    -flags               to print VM flags

    -sysprops            to print Java system properties

    <no option>          to print both of the above

    -h | -help           to print this help message

javah

生成本地方法的头文件