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Java常用知识.md

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Java常用命令

好记性不如烂笔头，jvm部分最优参数可视化生成网站 https://opts.console.perfma.com/

# 2核4G内存的生成的最优配置参数例子
-Xmx2688M -Xms2688M -Xmn960M -XX:MaxMetaspaceSize=512M -XX:MetaspaceSize=512M -XX:+UseConcMarkSweepGC -XX:+UseCMSInitiatingOccupancyOnly -XX:CMSInitiatingOccupancyFraction=70 -XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses -XX:+CMSClassUnloadingEnabled -XX:+ParallelRefProcEnabled -XX:+CMSScavengeBeforeRemark -XX:ErrorFile=/opt/soft/services/hs_err_pid%p.log   -Xloggc:/opt/soft/services/gc.log -XX:+PrintGCDetails -XX:+PrintGCDateStamps -verbose:class -XX:+PrintCommandLineFlags

后台运行Java服务的脚本命令

nohup java -Xmx64m -Xms64m -Xmn32m -Xss256k -jar -XX:ParallelGCThreads=2 -Djava.compiler=NONE springboot-web-memory-test-0.0.1-SNAPSHOT.jar > log.file  2>&1 &
nohup java -Xmx64m -Xms64m -Xmn32m -Xss256k -jar -XX:ParallelGCThreads=2 springboot-web-memory-test-0.0.1-SNAPSHOT.jar > log.file  2>&1 &

#!/bin/bash

java -Xmx2560m -Xms256m -Xmn128m -Xss1m -jar ureport2-springboot-1.0.0.jar --server.port=9898 >> log.log &
# chmod a+x run.sh

# http://localhost:9898/ureport/designer

java内存压榨

java -Xmx64m -Xms64m -Xmn32m -Xss1m -jar springboot-web-memory-test-0.0.1-SNAPSHOT.jar
# JVM默认线程栈大小是1M，一个线程默认分配的内存是1M
java -Xmx64m -Xms64m -Xmn32m -Xss256k -jar -XX:ParallelGCThreads=2 springboot-web-memory-test-0.0.1-SNAPSHOT.jar
# C2CompilerThread：JIT编译线程，动态编译Java运行代码，JIT是JVM为了优化执行频率比较高的字节码设计的技术，JIT把字节码编译为机器码，之后执行则不需要解释字节码，直接运行机器码即可。我们的服务没有什么负载，即使不优化也不受影响，这里的优化是把JIT关掉，在Java启动的参数中添加 => -Djava.compiler=NONE，这样就不会再有CompilerThread了
java -Xmx64m -Xms64m -Xmn32m -Xss256k -jar -XX:ParallelGCThreads=2 -Djava.compiler=NONE springboot-web-memory-test-0.0.1-SNAPSHOT.jar

gradle打包要添加的groovy脚本

buildscript {
    ext {
        springBootVersion = '1.5.13.RELEASE'
    }
    repositories {
        mavenLocal()
        maven{ url "http://maven.aliyun.com/nexus/content/groups/public/"}
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}
apply plugin: 'org.springframework.boot'

maven仓库的网页查看地址http://maven.aliyun.com/mvn/view

仓库 仓库类型 仓库存储策略 阿里云的映射地址
Repository Type Policy Path
apache snapshots proxy SNAPSHOT https://maven.aliyun.com/repository/apache-snapshots
central proxy RELEASE https://maven.aliyun.com/repository/central
google proxy RELEASE https://maven.aliyun.com/repository/google
gradle-plugin proxy RELEASE https://maven.aliyun.com/repository/gradle-plugin
jcenter proxy RELEASE https://maven.aliyun.com/repository/jcenter
spring proxy RELEASE https://maven.aliyun.com/repository/spring
spring-plugin proxy RELEASE https://maven.aliyun.com/repository/spring-plugin
public group RELEASE https://maven.aliyun.com/repository/public
releases hosted RELEASE https://maven.aliyun.com/repository/releases
snapshots hosted SNAPSHOT https://maven.aliyun.com/repository/snapshots
grails-core proxy RELEASE https://maven.aliyun.com/repository/grails-core

maven的settings.xml配置文件, mirrorOf的名称都设为 central , 好像maven下载插件时，默认是通过central的mirror对应的URL去查找，找遍了自定义的central后，再去官方默认的central找

<mirrors>
    <mirror>
        <id>aliyun-central</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-central</name>
        <url>https://maven.aliyun.com/repository/central</url>
    </mirror>
    <mirror>
        <id>aliyun-jcenter</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-jcenter</name>
        <url>https://maven.aliyun.com/repository/jcenter</url>
    </mirror>
    <mirror>
        <id>nexus-aliyun</id>
        <mirrorOf>central</mirrorOf>
        <name>Nexus aliyun</name>
        <url>http://maven.aliyun.com/nexus/content/groups/public</url>
    </mirror> 
    <mirror>
        <id>aliyun-apache</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-apache</name>
        <url>https://maven.aliyun.com/repository/apache-snapshots</url>
    </mirror>
    <mirror>
        <id>aliyun-google</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-google</name>
        <url>https://maven.aliyun.com/repository/google</url>
    </mirror>
    <mirror>
        <id>aliyun-gradle-plugin</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-gradle-plugin</name>
        <url>https://maven.aliyun.com/repository/gradle-plugin</url>
    </mirror>
    <mirror>
        <id>aliyun-gradle-plugin</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-gradle-plugin</name>
        <url>https://maven.aliyun.com/repository/gradle-plugin</url>
    </mirror>
    <mirror>
        <id>aliyun-spring</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-spring</name>
        <url>https://maven.aliyun.com/repository/spring</url>
    </mirror>
    <mirror>
        <id>aliyun-spring-plugin</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-spring-plugin</name>
        <url>https://maven.aliyun.com/repository/spring-plugin</url>
    </mirror>
    <mirror>
        <id>aliyun-public</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-public</name>
        <url>https://maven.aliyun.com/repository/public</url>
    </mirror>
    <mirror>
        <id>aliyun-releases</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-releases</name>
        <url>https://maven.aliyun.com/repository/releases</url>
    </mirror>
    <mirror>
        <id>aliyun-snapshots</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-snapshots</name>
        <url>https://maven.aliyun.com/repository/snapshots</url>
    </mirror>
    <mirror>
        <id>aliyun-grails-core</id>
        <mirrorOf>central</mirrorOf>
        <name>aliyun-grails-core</name>
        <url>https://maven.aliyun.com/repository/grails-core</url>
    </mirror>
</mirrors>

build.gradle配置文件

repositories {
    mavenLocal()
    maven{ url "https://maven.aliyun.com/repository/central"}
    maven{ url "https://maven.aliyun.com/repository/jcenter"}
    maven{ url "https://maven.aliyun.com/repository/apache-snapshots"}
    maven{ url "https://maven.aliyun.com/repository/google"}
    maven{ url "https://maven.aliyun.com/repository/gradle-plugin"}
    maven{ url "https://maven.aliyun.com/repository/spring"}
    maven{ url "https://maven.aliyun.com/repository/spring-plugin"}
    maven{ url "https://maven.aliyun.com/repository/public"}
    maven{ url "https://maven.aliyun.com/repository/releases"}
    maven{ url "https://maven.aliyun.com/repository/snapshots"}
    maven{ url "https://maven.aliyun.com/repository/grails-core"}
    mavenCentral()
}