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The System.java Java example source code
/*
* Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.lang;
import java.io.*;
import java.lang.reflect.Executable;
import java.lang.annotation.Annotation;
import java.security.AccessControlContext;
import java.util.Properties;
import java.util.PropertyPermission;
import java.util.StringTokenizer;
import java.util.Map;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.AllPermission;
import java.nio.channels.Channel;
import java.nio.channels.spi.SelectorProvider;
import sun.nio.ch.Interruptible;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
import sun.security.util.SecurityConstants;
import sun.reflect.annotation.AnnotationType;
/**
* The <code>System class contains several useful class fields
* and methods. It cannot be instantiated.
*
* <p>Among the facilities provided by the System class
* are standard input, standard output, and error output streams;
* access to externally defined properties and environment
* variables; a means of loading files and libraries; and a utility
* method for quickly copying a portion of an array.
*
* @author unascribed
* @since JDK1.0
*/
public final class System {
/* register the natives via the static initializer.
*
* VM will invoke the initializeSystemClass method to complete
* the initialization for this class separated from clinit.
* Note that to use properties set by the VM, see the constraints
* described in the initializeSystemClass method.
*/
private static native void registerNatives();
static {
registerNatives();
}
/** Don't let anyone instantiate this class */
private System() {
}
/**
* The "standard" input stream. This stream is already
* open and ready to supply input data. Typically this stream
* corresponds to keyboard input or another input source specified by
* the host environment or user.
*/
public final static InputStream in = null;
/**
* The "standard" output stream. This stream is already
* open and ready to accept output data. Typically this stream
* corresponds to display output or another output destination
* specified by the host environment or user.
* <p>
* For simple stand-alone Java applications, a typical way to write
* a line of output data is:
* <blockquote>
* System.out.println(data)
* </pre>
* <p>
* See the <code>println methods in class PrintStream.
*
* @see java.io.PrintStream#println()
* @see java.io.PrintStream#println(boolean)
* @see java.io.PrintStream#println(char)
* @see java.io.PrintStream#println(char[])
* @see java.io.PrintStream#println(double)
* @see java.io.PrintStream#println(float)
* @see java.io.PrintStream#println(int)
* @see java.io.PrintStream#println(long)
* @see java.io.PrintStream#println(java.lang.Object)
* @see java.io.PrintStream#println(java.lang.String)
*/
public final static PrintStream out = null;
/**
* The "standard" error output stream. This stream is already
* open and ready to accept output data.
* <p>
* Typically this stream corresponds to display output or another
* output destination specified by the host environment or user. By
* convention, this output stream is used to display error messages
* or other information that should come to the immediate attention
* of a user even if the principal output stream, the value of the
* variable <code>out, has been redirected to a file or other
* destination that is typically not continuously monitored.
*/
public final static PrintStream err = null;
/* The security manager for the system.
*/
private static volatile SecurityManager security = null;
/**
* Reassigns the "standard" input stream.
*
* <p>First, if there is a security manager, its checkPermission
* method is called with a <code>RuntimePermission("setIO") permission
* to see if it's ok to reassign the "standard" input stream.
* <p>
*
* @param in the new standard input stream.
*
* @throws SecurityException
* if a security manager exists and its
* <code>checkPermission method doesn't allow
* reassigning of the standard input stream.
*
* @see SecurityManager#checkPermission
* @see java.lang.RuntimePermission
*
* @since JDK1.1
*/
public static void setIn(InputStream in) {
checkIO();
setIn0(in);
}
/**
* Reassigns the "standard" output stream.
*
* <p>First, if there is a security manager, its checkPermission
* method is called with a <code>RuntimePermission("setIO") permission
* to see if it's ok to reassign the "standard" output stream.
*
* @param out the new standard output stream
*
* @throws SecurityException
* if a security manager exists and its
* <code>checkPermission method doesn't allow
* reassigning of the standard output stream.
*
* @see SecurityManager#checkPermission
* @see java.lang.RuntimePermission
*
* @since JDK1.1
*/
public static void setOut(PrintStream out) {
checkIO();
setOut0(out);
}
/**
* Reassigns the "standard" error output stream.
*
* <p>First, if there is a security manager, its checkPermission
* method is called with a <code>RuntimePermission("setIO") permission
* to see if it's ok to reassign the "standard" error output stream.
*
* @param err the new standard error output stream.
*
* @throws SecurityException
* if a security manager exists and its
* <code>checkPermission method doesn't allow
* reassigning of the standard error output stream.
*
* @see SecurityManager#checkPermission
* @see java.lang.RuntimePermission
*
* @since JDK1.1
*/
public static void setErr(PrintStream err) {
checkIO();
setErr0(err);
}
private static volatile Console cons = null;
/**
* Returns the unique {@link java.io.Console Console} object associated
* with the current Java virtual machine, if any.
*
* @return The system console, if any, otherwise <tt>null.
*
* @since 1.6
*/
public static Console console() {
if (cons == null) {
synchronized (System.class) {
cons = sun.misc.SharedSecrets.getJavaIOAccess().console();
}
}
return cons;
}
/**
* Returns the channel inherited from the entity that created this
* Java virtual machine.
*
* <p> This method returns the channel obtained by invoking the
* {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
* inheritedChannel} method of the system-wide default
* {@link java.nio.channels.spi.SelectorProvider} object. </p>
*
* <p> In addition to the network-oriented channels described in
* {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
* inheritedChannel}, this method may return other kinds of
* channels in the future.
*
* @return The inherited channel, if any, otherwise <tt>null.
*
* @throws IOException
* If an I/O error occurs
*
* @throws SecurityException
* If a security manager is present and it does not
* permit access to the channel.
*
* @since 1.5
*/
public static Channel inheritedChannel() throws IOException {
return SelectorProvider.provider().inheritedChannel();
}
private static void checkIO() {
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("setIO"));
}
}
private static native void setIn0(InputStream in);
private static native void setOut0(PrintStream out);
private static native void setErr0(PrintStream err);
/**
* Sets the System security.
*
* <p> If there is a security manager already installed, this method first
* calls the security manager's <code>checkPermission method
* with a <code>RuntimePermission("setSecurityManager")
* permission to ensure it's ok to replace the existing
* security manager.
* This may result in throwing a <code>SecurityException.
*
* <p> Otherwise, the argument is established as the current
* security manager. If the argument is <code>null and no
* security manager has been established, then no action is taken and
* the method simply returns.
*
* @param s the security manager.
* @exception SecurityException if the security manager has already
* been set and its <code>checkPermission method
* doesn't allow it to be replaced.
* @see #getSecurityManager
* @see SecurityManager#checkPermission
* @see java.lang.RuntimePermission
*/
public static
void setSecurityManager(final SecurityManager s) {
try {
s.checkPackageAccess("java.lang");
} catch (Exception e) {
// no-op
}
setSecurityManager0(s);
}
private static synchronized
void setSecurityManager0(final SecurityManager s) {
SecurityManager sm = getSecurityManager();
if (sm != null) {
// ask the currently installed security manager if we
// can replace it.
sm.checkPermission(new RuntimePermission
("setSecurityManager"));
}
if ((s != null) && (s.getClass().getClassLoader() != null)) {
// New security manager class is not on bootstrap classpath.
// Cause policy to get initialized before we install the new
// security manager, in order to prevent infinite loops when
// trying to initialize the policy (which usually involves
// accessing some security and/or system properties, which in turn
// calls the installed security manager's checkPermission method
// which will loop infinitely if there is a non-system class
// (in this case: the new security manager class) on the stack).
AccessController.doPrivileged(new PrivilegedAction<Object>() {
public Object run() {
s.getClass().getProtectionDomain().implies
(SecurityConstants.ALL_PERMISSION);
return null;
}
});
}
security = s;
}
/**
* Gets the system security interface.
*
* @return if a security manager has already been established for the
* current application, then that security manager is returned;
* otherwise, <code>null is returned.
* @see #setSecurityManager
*/
public static SecurityManager getSecurityManager() {
return security;
}
/**
* Returns the current time in milliseconds. Note that
* while the unit of time of the return value is a millisecond,
* the granularity of the value depends on the underlying
* operating system and may be larger. For example, many
* operating systems measure time in units of tens of
* milliseconds.
*
* <p> See the description of the class Date for
* a discussion of slight discrepancies that may arise between
* "computer time" and coordinated universal time (UTC).
*
* @return the difference, measured in milliseconds, between
* the current time and midnight, January 1, 1970 UTC.
* @see java.util.Date
*/
public static native long currentTimeMillis();
/**
* Returns the current value of the running Java Virtual Machine's
* high-resolution time source, in nanoseconds.
*
* <p>This method can only be used to measure elapsed time and is
* not related to any other notion of system or wall-clock time.
* The value returned represents nanoseconds since some fixed but
* arbitrary <i>origin time (perhaps in the future, so values
* may be negative). The same origin is used by all invocations of
* this method in an instance of a Java virtual machine; other
* virtual machine instances are likely to use a different origin.
*
* <p>This method provides nanosecond precision, but not necessarily
* nanosecond resolution (that is, how frequently the value changes)
* - no guarantees are made except that the resolution is at least as
* good as that of {@link #currentTimeMillis()}.
*
* <p>Differences in successive calls that span greater than
* approximately 292 years (2<sup>63 nanoseconds) will not
* correctly compute elapsed time due to numerical overflow.
*
* <p>The values returned by this method become meaningful only when
* the difference between two such values, obtained within the same
* instance of a Java virtual machine, is computed.
*
* <p> For example, to measure how long some code takes to execute:
* <pre> {@code
* long startTime = System.nanoTime();
* // ... the code being measured ...
* long estimatedTime = System.nanoTime() - startTime;}</pre>
*
* <p>To compare two nanoTime values
* <pre> {@code
* long t0 = System.nanoTime();
* ...
* long t1 = System.nanoTime();}</pre>
*
* one should use {@code t1 - t0 < 0}, not {@code t1 < t0},
* because of the possibility of numerical overflow.
*
* @return the current value of the running Java Virtual Machine's
* high-resolution time source, in nanoseconds
* @since 1.5
*/
public static native long nanoTime();
/**
* Copies an array from the specified source array, beginning at the
* specified position, to the specified position of the destination array.
* A subsequence of array components are copied from the source
* array referenced by <code>src to the destination array
* referenced by <code>dest. The number of components copied is
* equal to the <code>length argument. The components at
* positions <code>srcPos through
* <code>srcPos+length-1 in the source array are copied into
* positions <code>destPos through
* <code>destPos+length-1, respectively, of the destination
* array.
* <p>
* If the <code>src and dest arguments refer to the
* same array object, then the copying is performed as if the
* components at positions <code>srcPos through
* <code>srcPos+length-1 were first copied to a temporary
* array with <code>length components and then the contents of
* the temporary array were copied into positions
* <code>destPos through destPos+length-1 of the
* destination array.
* <p>
* If <code>dest is null, then a
* <code>NullPointerException is thrown.
* <p>
* If <code>src is null, then a
* <code>NullPointerException is thrown and the destination
* array is not modified.
* <p>
* Otherwise, if any of the following is true, an
* <code>ArrayStoreException is thrown and the destination is
* not modified:
* <ul>
* <li>The src argument refers to an object that is not an
* array.
* <li>The dest argument refers to an object that is not an
* array.
* <li>The src argument and dest argument refer
* to arrays whose component types are different primitive types.
* <li>The src argument refers to an array with a primitive
* component type and the <code>dest argument refers to an array
* with a reference component type.
* <li>The src argument refers to an array with a reference
* component type and the <code>dest argument refers to an array
* with a primitive component type.
* </ul>
* <p>
* Otherwise, if any of the following is true, an
* <code>IndexOutOfBoundsException is
* thrown and the destination is not modified:
* <ul>
* <li>The srcPos argument is negative.
* <li>The destPos argument is negative.
* <li>The length argument is negative.
* <li>srcPos+length is greater than
* <code>src.length, the length of the source array.
* <li>destPos+length is greater than
* <code>dest.length, the length of the destination array.
* </ul>
* <p>
* Otherwise, if any actual component of the source array from
* position <code>srcPos through
* <code>srcPos+length-1 cannot be converted to the component
* type of the destination array by assignment conversion, an
* <code>ArrayStoreException is thrown. In this case, let
* <b>k be the smallest nonnegative integer less than
* length such that <code>src[srcPos+k]
* cannot be converted to the component type of the destination
* array; when the exception is thrown, source array components from
* positions <code>srcPos through
* <code>srcPos+k-1
* will already have been copied to destination array positions
* <code>destPos through
* <code>destPos+k-1 and no other
* positions of the destination array will have been modified.
* (Because of the restrictions already itemized, this
* paragraph effectively applies only to the situation where both
* arrays have component types that are reference types.)
*
* @param src the source array.
* @param srcPos starting position in the source array.
* @param dest the destination array.
* @param destPos starting position in the destination data.
* @param length the number of array elements to be copied.
* @exception IndexOutOfBoundsException if copying would cause
* access of data outside array bounds.
* @exception ArrayStoreException if an element in the <code>src
* array could not be stored into the <code>dest array
* because of a type mismatch.
* @exception NullPointerException if either <code>src or
* <code>dest is null.
*/
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length);
/**
* Returns the same hash code for the given object as
* would be returned by the default method hashCode(),
* whether or not the given object's class overrides
* hashCode().
* The hash code for the null reference is zero.
*
* @param x object for which the hashCode is to be calculated
* @return the hashCode
* @since JDK1.1
*/
public static native int identityHashCode(Object x);
/**
* System properties. The following properties are guaranteed to be defined:
* <dl>
* <dt>java.version Java version number
* <dt>java.vendor Java vendor specific string
* <dt>java.vendor.url Java vendor URL
* <dt>java.home Java installation directory
* <dt>java.class.version Java class version number
* <dt>java.class.path Java classpath
* <dt>os.name Operating System Name
* <dt>os.arch Operating System Architecture
* <dt>os.version Operating System Version
* <dt>file.separator File separator ("/" on Unix)
* <dt>path.separator Path separator (":" on Unix)
* <dt>line.separator Line separator ("\n" on Unix)
* <dt>user.name User account name
* <dt>user.home User home directory
* <dt>user.dir User's current working directory
* </dl>
*/
private static Properties props;
private static native Properties initProperties(Properties props);
/**
* Determines the current system properties.
* <p>
* First, if there is a security manager, its
* <code>checkPropertiesAccess 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 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>Key |
* <th>Description of Associated Value |
* <tr>java.version |
* <td>Java Runtime Environment version
* <tr>java.vendor |
* <td>Java Runtime Environment vendor
* <tr>java.vendor.url |
* <td>Java vendor URL
* <tr>java.home |
* <td>Java installation directory
* <tr>java.vm.specification.version |
* <td>Java Virtual Machine specification version
* <tr>java.vm.specification.vendor |
* <td>Java Virtual Machine specification vendor
* <tr>java.vm.specification.name |
* <td>Java Virtual Machine specification name
* <tr>java.vm.version |
* <td>Java Virtual Machine implementation version
* <tr>java.vm.vendor |
* <td>Java Virtual Machine implementation vendor
* <tr>java.vm.name |
* <td>Java Virtual Machine implementation name
* <tr>java.specification.version |
* <td>Java Runtime Environment specification version
* <tr>java.specification.vendor |
* <td>Java Runtime Environment specification vendor
* <tr>java.specification.name |
* <td>Java Runtime Environment specification name
* <tr>java.class.version |
* <td>Java class format version number
* <tr>java.class.path |
* <td>Java class path
* <tr>java.library.path |
* <td>List of paths to search when loading libraries
* <tr>java.io.tmpdir |
* <td>Default temp file path
* <tr>java.compiler |
* <td>Name of JIT compiler to use
* <tr>java.ext.dirs |
* <td>Path of extension directory or directories
* <tr>os.name |
* <td>Operating system name
* <tr>os.arch |
* <td>Operating system architecture
* <tr>os.version |
* <td>Operating system version
* <tr>file.separator |
* <td>File separator ("/" on UNIX)
* <tr>path.separator |
* <td>Path separator (":" on UNIX)
* <tr>line.separator |
* <td>Line separator ("\n" on UNIX)
* <tr>user.name |
* <td>User's account name
* <tr>user.home |
* <td>User's home directory
* <tr>user.dir |
* <td>User's current working directory
* </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 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 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;
}
/**
* Returns the system-dependent line separator string. It always
* returns the same value - the initial value of the {@linkplain
* #getProperty(String) system property} {@code line.separator}.
*
* <p>On UNIX systems, it returns {@code "\n"}; on Microsoft
* Windows systems it returns {@code "\r\n"}.
*
* @return the system-dependent line separator string
* @since 1.7
*/
public static String lineSeparator() {
return lineSeparator;
}
private static String lineSeparator;
/**
* Sets the system properties to the <code>Properties
* argument.
* <p>
* First, if there is a security manager, its
* <code>checkPropertiesAccess method is called with no
* arguments. This may result in a security exception.
* <p>
* The argument becomes the current set of system properties for use
* by the {@link #getProperty(String)} method. If the argument is
* <code>null, then the current set of system properties is
* forgotten.
*
* @param props the new system properties.
* @exception SecurityException if a security manager exists and its
* <code>checkPropertiesAccess method doesn't allow access
* to the system properties.
* @see #getProperties
* @see java.util.Properties
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkPropertiesAccess()
*/
public static void setProperties(Properties props) {
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPropertiesAccess();
}
if (props == null) {
props = new Properties();
initProperties(props);
}
System.props = props;
}
/**
* Gets the system property indicated by the specified key.
* <p>
* First, if there is a security manager, its
* <code>checkPropertyAccess method is called with the key as
* its argument. This may result in a SecurityException.
* <p>
* If there is no current set of system properties, a set of system
* properties is first created and initialized in the same manner as
* for the <code>getProperties method.
*
* @param key the name of the system property.
* @return the string value of the system property,
* or <code>null if there is no property with that key.
*
* @exception SecurityException if a security manager exists and its
* <code>checkPropertyAccess method doesn't allow
* access to the specified system property.
* @exception NullPointerException if <code>key is
* <code>null.
* @exception IllegalArgumentException if <code>key is empty.
* @see #setProperty
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
* @see java.lang.System#getProperties()
*/
public static String getProperty(String key) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPropertyAccess(key);
}
return props.getProperty(key);
}
/**
* Gets the system property indicated by the specified key.
* <p>
* First, if there is a security manager, its
* <code>checkPropertyAccess method is called with the
* <code>key as its argument.
* <p>
* If there is no current set of system properties, a set of system
* properties is first created and initialized in the same manner as
* for the <code>getProperties method.
*
* @param key the name of the system property.
* @param def a default value.
* @return the string value of the system property,
* or the default value if there is no property with that key.
*
* @exception SecurityException if a security manager exists and its
* <code>checkPropertyAccess method doesn't allow
* access to the specified system property.
* @exception NullPointerException if <code>key is
* <code>null.
* @exception IllegalArgumentException if <code>key is empty.
* @see #setProperty
* @see java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
* @see java.lang.System#getProperties()
*/
public static String getProperty(String key, String def) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPropertyAccess(key);
}
return props.getProperty(key, def);
}
/**
* Sets the system property indicated by the specified key.
* <p>
* First, if a security manager exists, its
* <code>SecurityManager.checkPermission method
* is called with a <code>PropertyPermission(key, "write")
* permission. This may result in a SecurityException being thrown.
* If no exception is thrown, the specified property is set to the given
* value.
* <p>
*
* @param key the name of the system property.
* @param value the value of the system property.
* @return the previous value of the system property,
* or <code>null if it did not have one.
*
* @exception SecurityException if a security manager exists and its
* <code>checkPermission method doesn't allow
* setting of the specified property.
* @exception NullPointerException if <code>key or
* <code>value is null.
* @exception IllegalArgumentException if <code>key is empty.
* @see #getProperty
* @see java.lang.System#getProperty(java.lang.String)
* @see java.lang.System#getProperty(java.lang.String, java.lang.String)
* @see java.util.PropertyPermission
* @see SecurityManager#checkPermission
* @since 1.2
*/
public static String setProperty(String key, String value) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new PropertyPermission(key,
SecurityConstants.PROPERTY_WRITE_ACTION));
}
return (String) props.setProperty(key, value);
}
/**
* Removes the system property indicated by the specified key.
* <p>
* First, if a security manager exists, its
* <code>SecurityManager.checkPermission method
* is called with a <code>PropertyPermission(key, "write")
* permission. This may result in a SecurityException being thrown.
* If no exception is thrown, the specified property is removed.
* <p>
*
* @param key the name of the system property to be removed.
* @return the previous string value of the system property,
* or <code>null if there was no property with that key.
*
* @exception SecurityException if a security manager exists and its
* <code>checkPropertyAccess method doesn't allow
* access to the specified system property.
* @exception NullPointerException if <code>key is
* <code>null.
* @exception IllegalArgumentException if <code>key is empty.
* @see #getProperty
* @see #setProperty
* @see java.util.Properties
* @see java.lang.SecurityException
* @see java.lang.SecurityManager#checkPropertiesAccess()
* @since 1.5
*/
public static String clearProperty(String key) {
checkKey(key);
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new PropertyPermission(key, "write"));
}
return (String) props.remove(key);
}
private static void checkKey(String key) {
if (key == null) {
throw new NullPointerException("key can't be null");
}
if (key.equals("")) {
throw new IllegalArgumentException("key can't be empty");
}
}
/**
* Gets the value of the specified environment variable. An
* environment variable is a system-dependent external named
* value.
*
* <p>If a security manager exists, its
* {@link SecurityManager#checkPermission checkPermission}
* method is called with a
* <code>{@link RuntimePermission}("getenv."+name)
* permission. This may result in a {@link SecurityException}
* being thrown. If no exception is thrown the value of the
* variable <code>name is returned.
*
* <p>System
* properties</i> and environment variables are both
* conceptually mappings between names and values. Both
* mechanisms can be used to pass user-defined information to a
* Java process. Environment variables have a more global effect,
* because they are visible to all descendants of the process
* which defines them, not just the immediate Java subprocess.
* They can have subtly different semantics, such as case
* insensitivity, on different operating systems. For these
* reasons, environment variables are more likely to have
* unintended side effects. It is best to use system properties
* where possible. Environment variables should be used when a
* global effect is desired, or when an external system interface
* requires an environment variable (such as <code>PATH).
*
* <p>On UNIX systems the alphabetic case of name is
* typically significant, while on Microsoft Windows systems it is
* typically not. For example, the expression
* <code>System.getenv("FOO").equals(System.getenv("foo"))
* is likely to be true on Microsoft Windows.
*
* @param name the name of the environment variable
* @return the string value of the variable, or <code>null
* if the variable is not defined in the system environment
* @throws NullPointerException if <code>name is null
* @throws SecurityException
* if a security manager exists and its
* {@link SecurityManager#checkPermission checkPermission}
* method doesn't allow access to the environment variable
* <code>name
* @see #getenv()
* @see ProcessBuilder#environment()
*/
public static String getenv(String name) {
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("getenv."+name));
}
return ProcessEnvironment.getenv(name);
}
/**
* Returns an unmodifiable string map view of the current system environment.
* The environment is a system-dependent mapping from names to
* values which is passed from parent to child processes.
*
* <p>If the system does not support environment variables, an
* empty map is returned.
*
* <p>The returned map will never contain null keys or values.
* Attempting to query the presence of a null key or value will
* throw a {@link NullPointerException}. Attempting to query
* the presence of a key or value which is not of type
* {@link String} will throw a {@link ClassCastException}.
*
* <p>The returned map and its collection views may not obey the
* general contract of the {@link Object#equals} and
* {@link Object#hashCode} methods.
*
* <p>The returned map is typically case-sensitive on all platforms.
*
* <p>If a security manager exists, its
* {@link SecurityManager#checkPermission checkPermission}
* method is called with a
* <code>{@link RuntimePermission}("getenv.*")
* permission. This may result in a {@link SecurityException} being
* thrown.
*
* <p>When passing information to a Java subprocess,
* <a href=#EnvironmentVSSystemProperties>system properties
* are generally preferred over environment variables.
*
* @return the environment as a map of variable names to values
* @throws SecurityException
* if a security manager exists and its
* {@link SecurityManager#checkPermission checkPermission}
* method doesn't allow access to the process environment
* @see #getenv(String)
* @see ProcessBuilder#environment()
* @since 1.5
*/
public static java.util.Map<String,String> getenv() {
SecurityManager sm = getSecurityManager();
if (sm != null) {
sm.checkPermission(new RuntimePermission("getenv.*"));
}
return ProcessEnvironment.getenv();
}
/**
* Terminates the currently running Java Virtual Machine. The
* argument serves as a status code; by convention, a nonzero status
* code indicates abnormal termination.
* <p>
* This method calls the <code>exit method in class
* <code>Runtime. This method never returns normally.
* <p>
* The call <code>System.exit(n) is effectively equivalent to
* the call:
* <blockquote>
* Runtime.getRuntime().exit(n)
* </pre>
*
* @param status exit status.
* @throws SecurityException
* if a security manager exists and its <code>checkExit
* method doesn't allow exit with the specified status.
* @see java.lang.Runtime#exit(int)
*/
public static void exit(int status) {
Runtime.getRuntime().exit(status);
}
/**
* Runs the garbage collector.
* <p>
* Calling the <code>gc method suggests that the Java Virtual
* Machine expend effort toward recycling unused objects in order to
* make the memory they currently occupy available for quick reuse.
* When control returns from the method call, the Java Virtual
* Machine has made a best effort to reclaim space from all discarded
* objects.
* <p>
* The call <code>System.gc() is effectively equivalent to the
* call:
* <blockquote>
* Runtime.getRuntime().gc()
* </pre>
*
* @see java.lang.Runtime#gc()
*/
public static void gc() {
Runtime.getRuntime().gc();
}
/**
* Runs the finalization methods of any objects pending finalization.
* <p>
* Calling this method suggests that the Java Virtual Machine expend
* effort toward running the <code>finalize methods of objects
* that have been found to be discarded but whose <code>finalize
* methods have not yet been run. When control returns from the
* method call, the Java Virtual Machine has made a best effort to
* complete all outstanding finalizations.
* <p>
* The call <code>System.runFinalization() is effectively
* equivalent to the call:
* <blockquote>
* Runtime.getRuntime().runFinalization()
* </pre>
*
* @see java.lang.Runtime#runFinalization()
*/
public static void runFinalization() {
Runtime.getRuntime().runFinalization();
}
/**
* Enable or disable finalization on exit; doing so specifies that the
* finalizers of all objects that have finalizers that have not yet been
* automatically invoked are to be run before the Java runtime exits.
* By default, finalization on exit is disabled.
*
* <p>If there is a security manager,
* its <code>checkExit method is first called
* with 0 as its argument to ensure the exit is allowed.
* This could result in a SecurityException.
*
* @deprecated This method is inherently unsafe. It may result in
* finalizers being called on live objects while other threads are
* concurrently manipulating those objects, resulting in erratic
* behavior or deadlock.
* @param value indicating enabling or disabling of finalization
* @throws SecurityException
* if a security manager exists and its <code>checkExit
* method doesn't allow the exit.
*
* @see java.lang.Runtime#exit(int)
* @see java.lang.Runtime#gc()
* @see java.lang.SecurityManager#checkExit(int)
* @since JDK1.1
*/
@Deprecated
public static void runFinalizersOnExit(boolean value) {
Runtime.runFinalizersOnExit(value);
}
/**
* Loads the native library specified by the filename argument. The filename
* argument must be an absolute path name.
*
* If the filename argument, when stripped of any platform-specific library
* prefix, path, and file extension, indicates a library whose name is,
* for example, L, and a native library called L is statically linked
* with the VM, then the JNI_OnLoad_L function exported by the library
* is invoked rather than attempting to load a dynamic library.
* A filename matching the argument does not have to exist in the
* file system.
* See the JNI Specification for more details.
*
* Otherwise, the filename argument is mapped to a native library image in
* an implementation-dependent manner.
*
* <p>
* The call <code>System.load(name) is effectively equivalent
* to the call:
* <blockquote>
* Runtime.getRuntime().load(name)
* </pre>
*
* @param filename the file to load.
* @exception SecurityException if a security manager exists and its
* <code>checkLink method doesn't allow
* loading of the specified dynamic library
* @exception UnsatisfiedLinkError if either the filename is not an
* absolute path name, the native library is not statically
* linked with the VM, or the library cannot be mapped to
* a native library image by the host system.
* @exception NullPointerException if <code>filename is
* <code>null
* @see java.lang.Runtime#load(java.lang.String)
* @see java.lang.SecurityManager#checkLink(java.lang.String)
*/
@CallerSensitive
public static void load(String filename) {
Runtime.getRuntime().load0(Reflection.getCallerClass(), filename);
}
/**
* Loads the native library specified by the <code>libname
* argument. The <code>libname argument must not contain any platform
* specific prefix, file extension or path. If a native library
* called <code>libname is statically linked with the VM, then the
* JNI_OnLoad_<code>libname function exported by the library is invoked.
* See the JNI Specification for more details.
*
* Otherwise, the libname argument is loaded from a system library
* location and mapped to a native library image in an implementation-
* dependent manner.
* <p>
* The call <code>System.loadLibrary(name) is effectively
* equivalent to the call
* <blockquote>
* Runtime.getRuntime().loadLibrary(name)
* </pre>
*
* @param libname the name of the library.
* @exception SecurityException if a security manager exists and its
* <code>checkLink method doesn't allow
* loading of the specified dynamic library
* @exception UnsatisfiedLinkError if either the libname argument
* contains a file path, the native library is not statically
* linked with the VM, or the library cannot be mapped to a
* native library image by the host system.
* @exception NullPointerException if <code>libname is
* <code>null
* @see java.lang.Runtime#loadLibrary(java.lang.String)
* @see java.lang.SecurityManager#checkLink(java.lang.String)
*/
@CallerSensitive
public static void loadLibrary(String libname) {
Runtime.getRuntime().loadLibrary0(Reflection.getCallerClass(), libname);
}
/**
* Maps a library name into a platform-specific string representing
* a native library.
*
* @param libname the name of the library.
* @return a platform-dependent native library name.
* @exception NullPointerException if <code>libname is
* <code>null
* @see java.lang.System#loadLibrary(java.lang.String)
* @see java.lang.ClassLoader#findLibrary(java.lang.String)
* @since 1.2
*/
public static native String mapLibraryName(String libname);
/**
* Create PrintStream for stdout/err based on encoding.
*/
private static PrintStream newPrintStream(FileOutputStream fos, String enc) {
if (enc != null) {
try {
return new PrintStream(new BufferedOutputStream(fos, 128), true, enc);
} catch (UnsupportedEncodingException uee) {}
}
return new PrintStream(new BufferedOutputStream(fos, 128), true);
}
/**
* Initialize the system class. Called after thread initialization.
*/
private static void initializeSystemClass() {
// VM might invoke JNU_NewStringPlatform() to set those encoding
// sensitive properties (user.home, user.name, boot.class.path, etc.)
// during "props" initialization, in which it may need access, via
// System.getProperty(), to the related system encoding property that
// have been initialized (put into "props") at early stage of the
// initialization. So make sure the "props" is available at the
// very beginning of the initialization and all system properties to
// be put into it directly.
props = new Properties();
initProperties(props); // initialized by the VM
// There are certain system configurations that may be controlled by
// VM options such as the maximum amount of direct memory and
// Integer cache size used to support the object identity semantics
// of autoboxing. Typically, the library will obtain these values
// from the properties set by the VM. If the properties are for
// internal implementation use only, these properties should be
// removed from the system properties.
//
// See java.lang.Integer.IntegerCache and the
// sun.misc.VM.saveAndRemoveProperties method for example.
//
// Save a private copy of the system properties object that
// can only be accessed by the internal implementation. Remove
// certain system properties that are not intended for public access.
sun.misc.VM.saveAndRemoveProperties(props);
lineSeparator = props.getProperty("line.separator");
sun.misc.Version.init();
FileInputStream fdIn = new FileInputStream(FileDescriptor.in);
FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);
FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);
setIn0(new BufferedInputStream(fdIn));
setOut0(newPrintStream(fdOut, props.getProperty("sun.stdout.encoding")));
setErr0(newPrintStream(fdErr, props.getProperty("sun.stderr.encoding")));
// Load the zip library now in order to keep java.util.zip.ZipFile
// from trying to use itself to load this library later.
loadLibrary("zip");
// Setup Java signal handlers for HUP, TERM, and INT (where available).
Terminator.setup();
// Initialize any miscellenous operating system settings that need to be
// set for the class libraries. Currently this is no-op everywhere except
// for Windows where the process-wide error mode is set before the java.io
// classes are used.
sun.misc.VM.initializeOSEnvironment();
// The main thread is not added to its thread group in the same
// way as other threads; we must do it ourselves here.
Thread current = Thread.currentThread();
current.getThreadGroup().add(current);
// register shared secrets
setJavaLangAccess();
// Subsystems that are invoked during initialization can invoke
// sun.misc.VM.isBooted() in order to avoid doing things that should
// wait until the application class loader has been set up.
// IMPORTANT: Ensure that this remains the last initialization action!
sun.misc.VM.booted();
}
private static void setJavaLangAccess() {
// Allow privileged classes outside of java.lang
sun.misc.SharedSecrets.setJavaLangAccess(new sun.misc.JavaLangAccess(){
public sun.reflect.ConstantPool getConstantPool(Class<?> klass) {
return klass.getConstantPool();
}
public boolean casAnnotationType(Class<?> klass, AnnotationType oldType, AnnotationType newType) {
return klass.casAnnotationType(oldType, newType);
}
public AnnotationType getAnnotationType(Class<?> klass) {
return klass.getAnnotationType();
}
public Map<Class getDeclaredAnnotationMap(Class klass) {
return klass.getDeclaredAnnotationMap();
}
public byte[] getRawClassAnnotations(Class<?> klass) {
return klass.getRawAnnotations();
}
public byte[] getRawClassTypeAnnotations(Class<?> klass) {
return klass.getRawTypeAnnotations();
}
public byte[] getRawExecutableTypeAnnotations(Executable executable) {
return Class.getExecutableTypeAnnotationBytes(executable);
}
public <E extends Enum
E[] getEnumConstantsShared(Class<E> klass) {
return klass.getEnumConstantsShared();
}
public void blockedOn(Thread t, Interruptible b) {
t.blockedOn(b);
}
public void registerShutdownHook(int slot, boolean registerShutdownInProgress, Runnable hook) {
Shutdown.add(slot, registerShutdownInProgress, hook);
}
public int getStackTraceDepth(Throwable t) {
return t.getStackTraceDepth();
}
public StackTraceElement getStackTraceElement(Throwable t, int i) {
return t.getStackTraceElement(i);
}
public String newStringUnsafe(char[] chars) {
return new String(chars, true);
}
public Thread newThreadWithAcc(Runnable target, AccessControlContext acc) {
return new Thread(target, acc);
}
public void invokeFinalize(Object o) throws Throwable {
o.finalize();
}
});
}
}
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