【10-26】java调试技术学习笔记

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