java 怎样获取instrumentation实例

一、java 怎样获取instrumentation实例

找到这里就是因为我想获取一个 Instrumentation实例,但又不知道更优雅的方法，参见下面的代码。谁有更简洁的方法，请跟贴！

如何获取 instrumentation实例：

packagecom.taotling.instrument.insance;

importjava.lang.instrument.Instrumentation;

publicstaticInstrumentationinstrumentation;

publicstaticvoidpremain(StringagentArgs,Instrumentationinst){

publicstaticInstrumentationgetInstrumentation(){

}

将上面的代码打为JAR包，比如我取名为 agent.jar,添加 META-INF/MANIFEST.MF,内容为:

将上面的代码打为JAR包，比如我取名为 agent.jar,添加 META-INF/MANIFEST.MF,内容为:

Premain-Class:com.taotling.instrument.insance.MyJVMTIAgent

然后在你要调用 Instrumentation实例的类比如 Test类,通过-javaagent VM选项使用这个上面的JAR包:

然后在你要调用 Instrumentation实例的类比如 Test类,通过-javaagent VM选项使用这个上面的JAR包:

java-javaagent:"F:\test\myagent.jar"Test

Test类代码

importcom.taotling.instrument.insance.MyJVMTIAgent;

importjava.lang.instrument.Instrumentation;

publicstaticvoidmain(String[]args)throwsInterruptedException{

Instrumentationinstrumentation=MyJVMTIAgent.getInstrumentation();

System.out.println("instrumentationinstance:"+instrumentation);

System.out.println("thesizeofemptyObjectinstanceis"+instrumentation.getObjectSize(newObject())+"bytes.");

二、java 编译优化问题

java编译的结果是字节码而不是二进制，所以在运行时vm的优化才是重要的，包括VM的回收策略、分配给VM内存的大小都能在一定程度上影响性能。Sun的VM支持热点编译，对高频执行的代码段翻译的2进制会进行缓存，这也是VM的一种优化。

IBM JVM处理数学运算速度最快，BEA JVM处理大量线程和网络socket性能最好，而Sun JVM处理通常的商业逻辑性能最好。不过Hotspot的Server mode被报告有稳定性的问题。

Java的最大优势不是体现在执行速度上，所以对Compiler的要求并不如c++那样高，代码级的优化还需要程序员本身的功底。

Usage: java [-options] class [args...]

or java [-options]-jar jarfile [args...]

-client to select the"client" VM

-server to select the"server" VM

-hotspot is a synonym for the"client" VM [deprecated]

-cp<class search path of directories and zip/jar files>

-classpath<class search path of directories and zip/jar files>

A; separated list of directories, JAR archives,

and ZIP archives to search for class files.

-version print product version and exit

require the specified version to run

-showversion print product version and continue

-jre-restrict-search|-jre-no-restrict-search

include/exclude user private JREs in the version search

-?-help print this help message

-X print help on non-standard options

-ea[:<packagename>...|:<classname>]

-enableassertions[:<packagename>...|:<classname>]

-da[:<packagename>...|:<classname>]

-disableassertions[:<packagename>...|:<classname>]

-agentlib:<libname>[=<options>]

load native agent library<libname>, e.g.-agentlib:hprof

see also,-agentlib:jdwp=help and-agentlib:hprof=help

-agentpath:<pathname>[=<options>]

load native agent library by full pathname

-javaagent:<jarpath>[=<options>]

load Java programming language agent, see

-Xmixed mixed mode execution(default)

-Xint interpreted mode execution only

-Xbootclasspath:<directories and zip/jar files separated by;>

set search path for bootstrap classes and resources

-Xbootclasspath/a:<directories and zip/jar files separated by;>

append to end of bootstrap class path

-Xbootclasspath/p:<directories and zip/jar files separated by;>

prepend in front of bootstrap class path

-Xnoclassgc disable class garbage collection

-Xincgc enable incremental garbage collection

-Xloggc:<file> log GC status to a file with time stamps

-Xbatch disable background compilation

-Xms<size> set initial Java heap size

-Xmx<size> set maximum Java heap size

-Xss<size> set java thread stack size

-Xprof output cpu profiling data

-Xfuture enable strictest checks, anticipating future default

-Xrs reduce use of OS signals by Java/VM(see

-Xcheck:jni perform additional checks for JNI functions

-Xshare:off do not attempt to use shared class data

-Xshare:auto use shared class data if possible(default)

-Xshare:on require using shared class data, otherwise fail.

在Java、J2EE大型应用中，JVM非标准参数的配置直接关系到整个系统的性能。

JVM非标准参数指的是JVM底层的一些配置参数，这些参数在一般开发中默认即可，不需

要任何配置。但是在生产环境中，为了提高性能，往往需要调整这些参数，以求系统达

另外这些参数的配置也是影响系统稳定性的一个重要因素，相信大多数Java开发人员都

见过“OutOfMemory”类型的错误。呵呵，这其中很可能就是JVM参数配置不当或者就没

为了说明这些参数，还需要说说JDK中的命令行工具一些知识做铺垫。

首先看如何获取这些命令配置信息说明：

假设你是windows平台，你安装了J2SDK，那么现在你从cmd控制台窗口进入J2SDK安装目

录下的bin目录，然后运行java命令，出现如下结果，这些就是包括java.exe工具的和

-----------------------------------------------------------------------

D:\j2sdk15\bin>java

Usage: java [-options] class [args...]

or java [-options]-jar jarfile [args...]

-client to select the"client" VM

-server to select the"server" VM

-hotspot is a synonym for the"client" VM [deprecated]

-cp<class search path of directories and zip/jar files>

-classpath<class search path of directories and zip/jar files>

A; separated list of directories, JAR archives,

and ZIP archives to search for class files.

-version print product version and exit

require the specified version to run

-showversion print product version and continue

-jre-restrict-search|-jre-no-restrict-search

include/exclude user private JREs in the version search

-?-help print this help message

-X print help on non-standard options

-ea[:<packagename>...|:<classname>]

-enableassertions[:<packagename>...|:<classname>]

-da[:<packagename>...|:<classname>]

-disableassertions[:<packagename>...|:<classname>]

-agentlib:<libname>[=<options>]

load native agent library<libname>, e.g.-agentlib:hprof

see also,-agentlib:jdwp=help and-agentlib:hprof=help

-agentpath:<pathname>[=<options>]

load native agent library by full pathname

-javaagent:<jarpath>[=<options>]

load Java programming language agent, see

-----------------------------------------------------------------------

在控制台输出信息中，有个-X（注意是大写）的命令，这个正是查看JVM配置参数的命

其次，用java-X命令查看JVM的配置说明：

运行后如下结果，这些就是配置JVM参数的秘密武器，这些信息都是英文的，为了方便

阅读，我根据自己的理解翻译成中文了（不准确的地方还请各位博友斧正）

-----------------------------------------------------------------------

D:\j2sdk15\bin>java-X

-Xmixed mixed mode execution(default)

-Xint interpreted mode execution only

-Xbootclasspath:<directories and zip/jar files separated by;>

set search path for bootstrap classes and resources

-Xbootclasspath/a:<directories and zip/jar files separated by;>

append to end of bootstrap class path

-Xbootclasspath/p:<directories and zip/jar files separated by;>

prepend in front of bootstrap class path

-Xnoclassgc disable class garbage collection

-Xincgc enable incremental garbage collection

-Xloggc:<file> log GC status to a file with time stamps

-Xbatch disable background compilation

-Xms<size> set initial Java heap size

-Xmx<size> set maximum Java heap size

-Xss<size> set java thread stack size

-Xprof output cpu profiling data

-Xfuture enable strictest checks, anticipating future default

-Xrs reduce use of OS signals by Java/VM(see

-Xcheck:jni perform additional checks for JNI functions

-Xshare:off do not attempt to use shared class data

-Xshare:auto use shared class data if possible(default)

-Xshare:on require using shared class data, otherwise fail.

The-X options are non-standard and subject to change without notice.

-----------------------------------------------------------------------

-----------------------------------------------------------------------

1、-Xmixed mixed mode execution(default)

2、-Xint interpreted mode execution only

3、-Xbootclasspath:<directories and zip/jar files separated by;>

set search path for bootstrap classes and resources

设置zip/jar资源或者类（.class文件）存放目录路径

3、-Xbootclasspath/a:<directories and zip/jar files separated by;>

append to end of bootstrap class path

追加zip/jar资源或者类（.class文件）存放目录路径

4、-Xbootclasspath/p:<directories and zip/jar files separated by;>

prepend in front of bootstrap class path

预先加载zip/jar资源或者类（.class文件）存放目录路径

5、-Xnoclassgc disable class garbage collection

6、-Xincgc enable incremental garbage collection

7、-Xloggc:<file> log GC status to a file with time stamps

8、-Xbatch disable background compilation

9、-Xms<size> set initial Java heap size

10、-Xmx<size> set maximum Java heap size

11、-Xss<size> set java thread stack size

12、-Xprof output cpu profiling data

13、-Xfuture enable strictest checks, anticipating future default

执行严格的代码检查，预测可能出现的情况

14、-Xrs reduce use of OS signals by Java/VM(see

15、-Xcheck:jni perform additional checks for JNI functions

16、-Xshare:off do not attempt to use shared class data

17、-Xshare:auto use shared class data if possible(default)

18、-Xshare:on require using shared class data, otherwise fail.

尽可能的使用共享类的数据，否则运行失败

The-X options are non-standard and subject to change without notice.