System.getProperty浅析

her0kings1ey

背景

最近在阅读一些框架代码中看到在代码中使用了System.getProperty来获取值，之前在想这个值是从哪里设置的呢？于是便写下这篇小文记录一下。

浅析

首先我们看看System.getProperties() 的注释。

/**
     * Determines the current system properties.
     * 得到当前系统属性
     * 

     * First, if there is a security manager, its
     * 首先，如果存在安全管理器，
     * checkPropertiesAccess method is called with no
     * arguments. This may result in a security exception.
     * 会调用其checkPropertiesAccess无参方法，有可能抛出安全异常
     * 

     * The current set of system properties for use by the
     * 当前系统属性集会通过Property对象返回（对象有getProperty()方法）
     * {@link #getProperty(String)} method is returned as a
     * Properties object. If there is no current set of
     * 如果当前没有系统属性集，会创建并初始化系统属性集。
     * system properties, a set of system properties is first created and
     * initialized. This set of system properties always includes values
     * 系统属性通常包括了
     * java.version、java.vendor等等
     * for the following keys:
     * 
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
     *     
     * 
Key
Description of Associated Value
java.version
Java Runtime Environment version
java.vendor
Java Runtime Environment vendor
java.vendor.url
Java vendor URL
java.home
Java installation directory
java.vm.specification.version
Java Virtual Machine specification version
java.vm.specification.vendor
Java Virtual Machine specification vendor
java.vm.specification.name
Java Virtual Machine specification name
java.vm.version
Java Virtual Machine implementation version
java.vm.vendor
Java Virtual Machine implementation vendor
java.vm.name
Java Virtual Machine implementation name
java.specification.version
Java Runtime Environment specification  version
java.specification.vendor
Java Runtime Environment specification  vendor
java.specification.name
Java Runtime Environment specification  name
java.class.version
Java class format version number
java.class.path
Java class path
java.library.path
List of paths to search when loading libraries
java.io.tmpdir
Default temp file path
java.compiler
Name of JIT compiler to use
java.ext.dirs
Path of extension directory or directories
     *         Deprecated. This property, and the mechanism
     *            which implements it, may be removed in a future
     *            release. 
os.name
Operating system name
os.arch
Operating system architecture
os.version
Operating system version
file.separator
File separator ("/" on UNIX)
path.separator
Path separator (":" on UNIX)
line.separator
Line separator ("\n" on UNIX)
user.name
User's account name
user.home
User's home directory
user.dir
User's current working directory
     * 

     * Multiple paths in a system property value are separated by the path
     * separator character of the platform.
     * 

     * Note that even if the security manager does not permit the
     * getProperties operation, it may choose to permit the
     * {@link #getProperty(String)} operation.
     *
     * @return     the system properties
     * @exception  SecurityException  if a security manager exists and its
     *             checkPropertiesAccess method doesn't allow access
     *              to the system properties.
     * @see        #setProperties
     * @see        java.lang.SecurityException
     * @see        java.lang.SecurityManager#checkPropertiesAccess()
     * @see        java.util.Properties
     */

从这里可以看到这里主要能够拿到一些关于Java的系统属性，如：java版本，java的vendor，操作系统版本等等。另外，还能够运行java命令时，通过-D参数来指定系统属性，这也就是在一些框架内我们会看见使用System.getProperty来获取一些我们自定义的属性值。

关于java System能获取的属性值，请看这里

什么时候要使用System.getProperty

1. 可以获取系统环境信息。

2. 作为轻量级的配置文件使用，如：可以配置项目的运行路径、项目的配置文件路径等等

​