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Java 技术，IBM 风格: 类共享

共享类特性帮助减少内存占用并改进启动性能


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清单 8. 使用 verboseIO

    C:\j9vmwi3223\sdk\jre\bin>java -cp . -Xshareclasses:name=cache1,verboseIO Hello
          
    [-Xshareclasses verbose I/O output enabled]
    Finding class java/lang/Object in shared cache for cldr id 0... Failed.
    Storing class java/lang/Object in shared cache for cldr id 0 with URL 
		C:\j9vmwi3223\sdk\jre\lib\vm.jar (index 0)... Succeeded.
    Finding class java/lang/J9VMInternals in shared cache for cldr id 0... Failed.
    Storing class java/lang/J9VMInternals in shared cache for cldr id 0 with URL 
		C:\j9vmwi3223\sdk\jre\lib\vm.jar (index 0)... Succeeded.
    Finding class java/lang/Class in shared cache for cldr id 0... Failed.
    Storing class java/lang/Class in shared cache for cldr id 0 with URL 
		C:\j9vmwi3223\sdk\jre\lib\vm.jar (index 0)... Succeeded.
    ...
    
    
    C:\j9vmwi3223\sdk\jre\bin>java -cp . -Xshareclasses:name=cache1,verboseIO Hello
          
    [-Xshareclasses verbose I/O output enabled]
    Finding class java/lang/Object in shared cache for cldr id 0... Succeeded.
    Finding class java/lang/J9VMInternals in shared cache for cldr id 0... Succeeded.
    Finding class java/lang/Class in shared cache for cldr id 0... Succeeded.
    ...

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清单 9. 来自 Helper API 的状态输出

    C:\j9vmwi3223\sdk\jre\bin>java -cp . -Xshareclasses:name=cache1,verboseHelper Hello
    
    [-Xshareclasses Helper API verbose output enabled]
    Info for SharedClassHelper id 1: Verbose output enabled for SharedClassHelper id 1
    Info for SharedClassHelper id 1: Created URLClasspathHelper with id 1, urlCount=15
    Info for SharedClassHelper id 2: Verbose output enabled for SharedClassHelper id 2
    Info for SharedClassHelper id 2: Created URLClasspathHelper with id 2, urlCount=1
    Info for SharedClassHelper id 1: There are no confirmed elements in the classpath. 
		Returning null.
    Info for SharedClassHelper id 2: There are no confirmed elements in the classpath. 
		Returning null.
    Info for SharedClassHelper id 2: Number of confirmed entries is now 1
    Hello

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清单 11. 运行启用了类共享的演示程序

    C:\j9vmwi3223\sdk\jre\bin>java -Xshareclasses:name=demo,verbose -Xscmx50M 
		-cp C:\shcdemo.jar ClassLoadStress
    [-Xshareclasses verbose output enabled]
    JVMSHRC158I Successfully created shared class cache "demo"
    JVMSHRC166I Attached to cache "demo", size=52428760 bytes
    JVMSHRC168I Total shared class bytes read=0. Total bytes stored=46055592

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清单 13. 从共享缓存读取类


    C:\j9vmwi3223\sdk\jre\bin>java -Xshareclasses:name=demo,verbose -Xscmx50M 
		-cp C:\shcdemo.jar ClassLoadStress
    [-Xshareclasses verbose output enabled]
    JVMSHRC159I Successfully opened shared class cache "demo"
    JVMSHRC166I Attached to cache "demo", size=52428760 bytes
    JVMSHRC168I Total shared class bytes read=45620448. Total bytes stored=1824

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