JVM的Client模式与Server模式

JVM有两种运行模式Server与Client。两种模式的区别在于，Client模式启动速度较快，Server模式启动较慢；但是启动进入稳定期长期运行之后Server模式的程序运行速度比Client要快很多。这是因为Server模式启动的JVM采用的是重量级的虚拟机，对程序采用了更多的优化；而Client模式启动的JVM采用的是轻量级的虚拟机。所以Server启动慢，但稳定后速度比Client远远要快。

一、当前是Client or Server

java -versinon

如下：

java version "1.8.0_144"                                                                                                
Java(TM) SE Runtime Environment (build 1.8.0_144-b01)                                                                 
Java HotSpot(TM) 64-Bit Server VM (build 25.144-b01, mixed mode)

二、Client 与 Server 切换

2.1、模式配置文件

JVM启动时采用何种模式是在名为jvm.cfg的配置文件中配置的。
配置文件的位置：

32位的虚拟机在%JAVA_HOME%/jre/lib/i386/jvm.cfg
64位的虚拟机在%JAVA_HOME%/jre/lib/amd64/jvm.cfg

打开32位的虚拟机对应的模式配置文件：

# Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
# ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
# List of JVMs that can be used as an option to java, javac, etc.
# Order is important -- first in this list is the default JVM.
# NOTE that this both this file and its format are UNSUPPORTED and
# WILL GO AWAY in a future release.
# You may also select a JVM in an arbitrary location with the
# "-XXaltjvm=<jvm_dir>" option, but that too is unsupported
# and may not be available in a future release.
 
-client KNOWN
-server KNOWN

第一行的模式 -client KNOWN 被作为虚拟机默认的运行模式，如果想让32位的虚拟机按照server模式运行，将第一行和第二行代码交换位置。
jvm.cfg中配置：（此时为client模式）

64位的虚拟机对应的模式匹配文件关于运行模式代码：