精简JRE - verbose命令

 

在控制台输入java后,从输出的帮助信息中能找到如下内容:
-verbose[:class|gc|jni]
              enable verbose output

 

-verbose:gc 输出虚拟机内存回收相关信息.
-verbose:jni 输出调用本地方法相关信息
-verbose:class(等同于-verbose) 输出虚拟机加载类相关信息.

 

借助-verbose命令,查看虚拟机在运行Java程序时所加载的所有类.
根据加载的类来裁剪JRE目录下类库(主要是rt.jar),辅助完成JRE的精简工作.

 

测试程序:

 

/*
@author jarg
@TODO 测试-verbose命令
*/
import java.io.InputStreamReader;
import java.io.IOException;

public class Hello
{
	public static void main(String[] args) throws IOException
	{
		InputStreamReader ir = new InputStreamReader(System.in);
		System.out.println("Hello");
		ir.read();
	}
}

 

命令测试:

java -verbose Hello>log.txt

注: 命令行尾>log.txt是输出结果保存到log.txt;不写则直接输出到控制台.

 

 

输出结果: 

 

[Loaded java.lang.Object from shared objects file]
[Loaded java.io.Serializable from shared objects file]
[Loaded java.lang.Comparable from shared objects file]
...
[Loaded java.lang.Math from shared objects file]
[Opened C:\Program Files\Java\jre\lib\rt.jar]
[Loaded java.nio.charset.Charset$3 from C:\Program Files\Java\jre\lib\rt.jar]
[Opened C:\Program Files\Java\jre\lib\charsets.jar]
[Loaded sun.nio.cs.AbstractCharsetProvider from C:\Program Files\Java\jre\lib\rt.jar]
[Loaded sun.nio.cs.ext.ExtendedCharsets from C:\Program Files\Java\jre\lib\charsets.jar]
[Loaded java.lang.Class$1 from shared objects file]
...
[Loaded Hello from file:/C:/Documents%20and%20Settings/Administrator/%e6%a1%8c%e9%9d%a2/loadDLL/]
Hello
[Loaded java.lang.Shutdown from shared objects file]
[Loaded java.lang.Shutdown$Lock from shared objects file]

 

从输出结果查看运行当前命令所需加载的类,根据这些类文件在rt.jar中目录层次关系复制出来.将这些类文件打包,并命名为rt.jar(即是精简后的rt.jar).