JDK and JRE File Structure JAVA_HOME HotSpot优化技术

https://docs.oracle.com/javase/8/docs/technotes/tools/windows/jdkfiles.html

Java Platform, Standard Edition Tools Reference
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3 JDK and JRE File Structure

This chapter introduces the JDK directories and the files they contain. The file structure of the JRE is identical to the structure of the jre directory in the JDK.

This chapter covers the following topics:

• Demos and Samples

• Development Files and Directories

• Additional Files and Directories

Demos and Samples

Demos and samples that show you how to program for the Java platform are available as a separate download at the Java SE Downloads page at
http://www.oracle.com/technetwork/java/javase/downloads/index.html

These are available as separate .tar.z compressed packages and .tar.gz compressed binaries. Similar to other 64-bit bundles on Oracle Solaris, the 64-bit demos and samples bundles on Oracle Solaris require that the 32-bit demos and samples bundles to also be installed.

Development Files and Directories

This section describes the most important files and directories required to develop applications for the Java platform. Some of the directories that are not required include Java source code and C header files. See Additional Files and Directories.

jdk1.8.0
     bin
          java*
          javac*
          javap*
          javah*
          javadoc*
     lib
          tools.jar
          dt.jar
     jre
          bin
               java*
          lib
               applet
               ext
                    jfxrt.jar
                    localdata.jar
               fonts
               security
               sparc
                    server
                    client
               rt.jar
               charsets.jar

Assuming the JDK software is installed at /jdk1.8.0, here are some of the most important directories:

/jdk1.8.0

Root directory of the JDK software installation. Contains copyright, license, and README files. Also contains src.zip, the archive of source code for the Java platform.

/jdk1.8.0/bin

Executables for all the development tools contained in the JDK. The PATH environment variable should contain an entry for this directory.

/jdk1.8.0/lib

Files used by the development tools. Includes tools.jar, which contains non-core classes for support of the tools and utilities in the JDK. Also includes dt.jar, the DesignTime archive of BeanInfo files that tell interactive development environments (IDEs) how to display the Java components and how to let the developer customize them for an application.

/jdk1.8.0/jre

Root directory of the Java Runtime Environment (JRE) used by the JDK development tools. The runtime environment is an implementation of the Java platform. This is the directory referred to by the java.home system property.

/jdk1.8.0/jre/bin

Executable files for tools and libraries used by the Java platform. The executable files are identical to files in /jdk1.8.0/bin. The java launcher tool serves as an application launcher (and replaced the earlier jre command that shipped with 1.1 releases of the JDK). This directory does not need to be in the PATH environment variable.

/jdk1.8.0/jre/lib

Code libraries, property settings, and resource files used by the JRE. For example rt.jar contains the bootstrap classes, which are the run time classes that comprise the Java platform core API, and charsets.jar contains the character-conversion classes. Aside from the ext subdirectory, there are several additional resource subdirectories not described here.

/jdk1.8.0/jre/lib/ext

Default installation directory for extensions to the Java platform. This is where the JavaHelp JAR file goes when it is installed, for example. This directory includes the jfxrt.jar file, which contains the JavaFX runtime libraries and the localedata.jar file, which contains the locale data for the java.text and java.util packages. See The Extension Mechanism at
http://docs.oracle.com/javase/8/docs/technotes/guides/extensions/index.html

/jdk1.8.0/jre/lib/security

Contains files used for security management. These include the security policy java.policy and security properties java.security files.

/jdk1.8.0/jre/lib/sparc

Contains the .so (shared object) files used by the Oracle Solaris release of the Java platform.

/jdk1.8.0/jre/lib/sparc/client

Contains the .so file used by the Java HotSpot VM client, which is implemented with Java HotSpot VM technology. This is the default Java Virtual Machine (JVM).

/jdk1.8.0/jre/lib/sparc/server

Contains the .so file used by the Java HotSpot VM server.

/jdk1.8.0/jre/lib/applet

JAR files that contain support classes for applets can be placed in the lib/applet/ directory. This reduces startup time for large applets by allowing applet classes to be preloaded from the local file system by the applet class loader and provides the same protections as though they had been downloaded over the Internet.

/jdk1.8.0/jre/lib/fonts

Font files used by the platform.

Additional Files and Directories

This section describes the directory structure for Java source code, C header files, and other additional directories and files.

jdk1.8.0
     db
     include
     man
     src.zip

/jdk1.8.0/src.zip

Archive that contains the source code for the Java platform.

/jdk1.8.0/db

Contains Java DB. See Java DB Technical Documentation at
http://docs.oracle.com/javadb/

/jdk1.8.0/include

C-language header files that support native-code programming with the Java Native Interface and the Java Virtual Machine (JVM) Debugger Interface. See Java Native Interface at
http://docs.oracle.com/javase/8/docs/technotes/guides/jni/index.html

See also Java Platform Debugger Architecture (JPDA) at
http://docs.oracle.com/javase/8/docs/technotes/guides/jpda/index.html

/jdk1.8.0/man

Contains man pages for the JDK tools.

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C:\Users\Administrator>scala
Welcome to Scala 2.12.6 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_171).
Type in expressions for evaluation. Or try :help.

scala>

JDK安装、java环境配置 - JupiterMouse - 博客园 https://www.cnblogs.com/renqiqiang/p/6822143.html

JDK JRE  区别

JDK是Java语言的软件开发工具包，主要用于移动设备、嵌入式设备上的java应用程序。JDK是整个java开发的核心，它包含了JAVA的运行环境，JAVA工具和JAVA基础的类库。

JRE（Java Runtime Environment，Java运行环境），运行JAVA程序所必须的环境的集合，包含JVM标准实现及Java核心类库.它包括Java虚拟机（jvm）、Java核心类库和支持文件。它不包含开发工具(JDK)--编译器、调试器和其它工具。如果只需要运行Java程序或Applet，下载并安装它即可。如果要自行开发 Java软件，要下载JDK(JRE和JDK的区别，没有JDK的话，无法编译Java程序，如果想只运行Java程序，要确保已安装相应的JRE)。在JDK中附带有JRE。SE(J2SE)，standard edition，标准版，是我们通常用的一个版本。EE(J2EE)，enterprise edition，企业版，使用这种JDK开发J2EE应用程序。ME(J2ME)，micro edition，主要用于移动设备、嵌入式设备上的java应用程序

Java虚拟机（JVM）允许将代码在一个平台上编写和编译后，近乎无须进一步处理地分发到其他的平台上。尽管跨平台的问题

没有并没有消失，但是跨平台的成本相比之前极大地降低了。

随着JVM执行效率的不断提高，HotSpot优化技术被发明出来，其原理：先探测运行环境，再进行针对性的代码优化

虽然这使得JVM启动速度变慢，但是之后的运行性能则变得很适合运行服务器之类的应用。尽管最初并非为企业服务器领域设计的，JVM开始在此领域大行其道。于是，人们开始尝试简化企业服务器应用开发，Enterprise Java Beans 、Spring Application Framework 出现。

Installing the JDK Software and Setting JAVA_HOME (Using the GlassFish ESB Installation GUI) https://docs.oracle.com/cd/E19182-01/821-0917/inst_jdk_javahome_t/index.html

To Install the JDK Software and Set JAVA_HOME on a UNIX System

1. To install the JDK software, do the following:

   1. Go to http://java.sun.com/javase/downloads/index.jsp.

   2. Select the appropriate JDK version and click Download.

      The JDK software is installed on your computer in the default location; for example, at /usr/jdk/jdk1.6.0_02. You can change this location.

2. To set JAVA_HOME, do one of the following:

   • For Korn and bash shells, run the following commands:

     export JAVA_HOME=jdk-install-dir

     export PATH=$JAVA_HOME/bin:$PATH

   • For the bourne shell, run the following commands:

     JAVA_HOME=jdk-install-dir

     export JAVA_HOME

     PATH=$JAVA_HOME/bin:$PATH

     export PATH

   • For the C shell, run the following commands:

     setenv JAVA_HOME jdk-install-dir

     setenv PATH $JAVA_HOME/bin:$PATH

     export PATH=$JAVA_HOME/bin:$PATH

3. Change the permissions to enable you to run the GlassFish ESB Installer by running the following command:

   chmod 755 JavaCAPS.bin

To Install the JDK Software and Set JAVA_HOME on a Windows System

1. To install the JDK software, do the following:

   1. Go to http://java.sun.com/javase/downloads/index.jsp.

   2. Select the appropriate JDK software and click Download.

      The JDK software is installed on your computer in the default location; for example, at C:\Program Files\Java\jdk1.6.0_02. You can move the JDK software to another location.

2. To set JAVA_HOME, do the following:

   1. Right click My Computer and select Properties.

   2. On the Advanced tab, select Environment Variables, and then edit JAVA_HOME to point to where the JDK software is located, for example, C:\Program Files\Java\jdk1.6.0_02.

【jps命令找不到】

rm -rf /usr/bin/java;ln -s /home/jdk1.8.0_171/bin/java /usr/bin/java;export PATH=$PATH:/home/jdk1.8.0_171/bin;

jps在home/jdk1.8.0_171/bin中。

Java Platform Standard Edition 8 Documentation https://docs.oracle.com/javase/8/docs/

JDK

Java Language

Java Language

Tools &
Tool APIs

java	javac	javadoc	jar	javap	jdeps	Scripting
Security	Monitoring	JConsole	VisualVM	JMC	JFR
JPDA	JVM TI	IDL	RMI	Java DB	Deployment
Internationalization		Web Services		Troubleshooting

JRE

Deployment

Java Web Start

Applet / Java Plug-in

User Interface
Toolkits

JavaFX

Swing	Java 2D	AWT	Accessibility
Drag and Drop	Input Methods	Image I/O	Print Service	Sound

Java SE
API

Integration
Libraries

IDL

JDBC

JNDI

RMI

RMI-IIOP

Scripting

Compact
Profiles

Other Base
Libraries

Beans	Security	Serialization	Extension Mechanism
JMX	XML JAXP	Networking	Override Mechanism
JNI	Date and Time	Input/Output	Internationalization

lang and util
Base Libraries

lang and util
Math	Collections	Ref Objects	Regular Expressions
Logging	Management	Instrumentation	Concurrency Utilities
Reflection	Versioning	Preferences API	JAR	Zip

Java Virtual Machine

Java HotSpot Client and Server VM