JDK8 JVM运行时系统级参数

System.*调用

 
    /**
     * Determines the current system properties.
     * <p>
     * First, if there is a security manager, its
     * <code>checkPropertiesAccess</code> method is called with no
     * arguments. This may result in a security exception.
     * <p>
     * The current set of system properties for use by the
     * {@link #getProperty(String)} method is returned as a
     * <code>Properties</code> object. If there is no current set of
     * system properties, a set of system properties is first created and
     * initialized. This set of system properties always includes values
     * for the following keys:
     * <table summary="Shows property keys and associated values">
     * <tr><th>Key</th>
     *     <th>Description of Associated Value</th></tr>
     * <tr><td><code>java.version</code></td>
     *     <td>Java Runtime Environment version</td></tr>
     * <tr><td><code>java.vendor</code></td>
     *     <td>Java Runtime Environment vendor</td></tr>
     * <tr><td><code>java.vendor.url</code></td>
     *     <td>Java vendor URL</td></tr>
     * <tr><td><code>java.home</code></td>
     *     <td>Java installation directory</td></tr>
     * <tr><td><code>java.vm.specification.version</code></td>
     *     <td>Java Virtual Machine specification version</td></tr>
     * <tr><td><code>java.vm.specification.vendor</code></td>
     *     <td>Java Virtual Machine specification vendor</td></tr>
     * <tr><td><code>java.vm.specification.name</code></td>
     *     <td>Java Virtual Machine specification name</td></tr>
     * <tr><td><code>java.vm.version</code></td>
     *     <td>Java Virtual Machine implementation version</td></tr>
     * <tr><td><code>java.vm.vendor</code></td>
     *     <td>Java Virtual Machine implementation vendor</td></tr>
     * <tr><td><code>java.vm.name</code></td>
     *     <td>Java Virtual Machine implementation name</td></tr>
     * <tr><td><code>java.specification.version</code></td>
     *     <td>Java Runtime Environment specification  version</td></tr>
     * <tr><td><code>java.specification.vendor</code></td>
     *     <td>Java Runtime Environment specification  vendor</td></tr>
     * <tr><td><code>java.specification.name</code></td>
     *     <td>Java Runtime Environment specification  name</td></tr>
     * <tr><td><code>java.class.version</code></td>
     *     <td>Java class format version number</td></tr>
     * <tr><td><code>java.class.path</code></td>
     *     <td>Java class path</td></tr>
     * <tr><td><code>java.library.path</code></td>
     *     <td>List of paths to search when loading libraries</td></tr>
     * <tr><td><code>java.io.tmpdir</code></td>
     *     <td>Default temp file path</td></tr>
     * <tr><td><code>java.compiler</code></td>
     *     <td>Name of JIT compiler to use</td></tr>
     * <tr><td><code>java.ext.dirs</code></td>
     *     <td>Path of extension directory or directories
     *         <b>Deprecated.</b> <i>This property, and the mechanism
     *            which implements it, may be removed in a future
     *            release.</i> </td></tr>
     * <tr><td><code>os.name</code></td>
     *     <td>Operating system name</td></tr>
     * <tr><td><code>os.arch</code></td>
     *     <td>Operating system architecture</td></tr>
     * <tr><td><code>os.version</code></td>
     *     <td>Operating system version</td></tr>
     * <tr><td><code>file.separator</code></td>
     *     <td>File separator ("/" on UNIX)</td></tr>
     * <tr><td><code>path.separator</code></td>
     *     <td>Path separator (":" on UNIX)</td></tr>
     * <tr><td><code>line.separator</code></td>
     *     <td>Line separator ("\n" on UNIX)</td></tr>
     * <tr><td><code>user.name</code></td>
     *     <td>User's account name</td></tr>
     * <tr><td><code>user.home</code></td>
     *     <td>User's home directory</td></tr>
     * <tr><td><code>user.dir</code></td>
     *     <td>User's current working directory</td></tr>
     * </table>
     * <p>
     * Multiple paths in a system property value are separated by the path
     * separator character of the platform.
     * <p>
     * Note that even if the security manager does not permit the
     * <code>getProperties</code> operation, it may choose to permit the
     * {@link #getProperty(String)} operation.
     *
     * @return     the system properties
     * @exception  SecurityException  if a security manager exists and its
     *             <code>checkPropertiesAccess</code> method doesn't allow access
     *              to the system properties.
     * @see        #setProperties
     * @see        java.lang.SecurityException
     * @see        java.lang.SecurityManager#checkPropertiesAccess()
     * @see        java.util.Properties
     */
    public static Properties getProperties() {
        SecurityManager sm = getSecurityManager();
        if (sm != null) {
            sm.checkPropertiesAccess();
        }
 
        return props;
    }