目录

查看

-fiags

-flag

设置值

扩展

java -XX:+PrintFlagsFinal

作用：实时查看和修改JVM配置参数

C:Usersqianqian>jinfo -h
Usage:
    jinfo [option] 
        (to connect to running process)
    jinfo [option] 
        (to connect to a core file)
    jinfo [option] [server_id@]
        (to connect to remote debug server)

where  is one of:
    -flag          to print the value of the named VM flag
    -flag [+|-]    to enable or disable the named VM flag
    -flag = to set the named VM flag to the given value
    -flags               to print VM flags
    -sysprops            to print Java system properties
              to print both of the above
    -h | -help           to print this help message

查看

-fiags

查看赋过值的参数

C:Usersqianqian>jinfo -flags 8740
Attaching to process ID 8740, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.211-b12
Non-default VM flags: -XX:-BytecodeVerificationLocal -XX:-BytecodeVerificationRemote 
-XX:CICompilerCount=3 -XX:ConcGCThreads=2 -XX:G1HeapRegionSize=1048576 
-XX:InitialHeapSize=268435456 -XX:+ManagementServer -XX:MarkStackSize=4194304 
-XX:MaxGCPauseMillis=100 -XX:MaxHeapSize=1073741824 -XX:MaxNewSize=643825664 
-XX:MinHeapDeltaBytes=1048576 -XX:TieredStopAtLevel=1 -XX:+UseCompressedClassPointers 
-XX:+UseCompressedOops -XX:+UseFastUnorderedTimeStamps -XX:+UseG1GC 
-XX:-UseLargePagesIndividualAllocation
Command line:  
-agentlib:jdwp=transport=dt_socket,address=127.0.0.1:54923,suspend=y,server=n 
-XX:+UseG1GC -Xmx1G -XX:MaxGCPauseMillis=100 -XX:TieredStopAtLevel=1 -Xverify:none 
-Dspring.output.ansi.enabled=always -Dcom.sun.management.jmxremote 
-Dspring.jmx.enabled=true -Dspring.liveBeansView.mbeanDomain 
-Dspring.application.admin.enabled=true 
-javaagent:C:UsersqianqianAppDataLocalJetBrainsIntelliJIdea2020.2captureAgentdebugger-agent.jar -Dfile.encoding=UTF-8

-flag

查看某个参数具体的值

C:Usersqianqian>jinfo -flag UseG1GC 8740
-XX:+UseG1GC

C:Usersqianqian>jinfo -flag MaxHeapSize 8740
-XX:MaxHeapSize=1073741824

设置值

参数被标记为manageable的flag才可以被实时修改。其实极其有限

C:Usersqianqian>jinfo -flag PrintGCDetails 8740
-XX:-PrintGCDetails

C:Usersqianqian>jinfo -flag +PrintGCDetails 8740

C:Usersqianqian>jinfo -flag PrintGCDetails 8740
-XX:+PrintGCDetails

C:Usersqianqian>jinfo -flag MaxHeapFreeRatio 8740
-XX:MaxHeapFreeRatio=70

C:Usersqianqian>jinfo -flag MaxHeapFreeRatio=100 8740

C:Usersqianqian>jinfo -flag MaxHeapFreeRatio 8740
-XX:MaxHeapFreeRatio=100

扩展

java -XX:+PrintFlagsFinal

C:Usersqianqian>java -XX:+PrintFlagsFinal > 1.txt