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Apache Commons Daemon software provides an alternative invocation mechanism for unix-daemon-like Java code.
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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* @version $Id: DaemonWrapper.java 1204007 2011-11-19 16:10:29Z ggregory $ */
package org.apache.commons.daemon.support;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import org.apache.commons.daemon.Daemon;
import org.apache.commons.daemon.DaemonContext;
/**
* Implementation of the Daemon that allows running
* standard applications as daemons.
* The applications must have the mechanism to manage
* the application lifecycle.
*
* @version $Id: DaemonWrapper.java 1204007 2011-11-19 16:10:29Z ggregory $
* @author Mladen Turk
*/
public class DaemonWrapper implements Daemon
{
private final static String ARGS = "args";
private final static String START_CLASS = "start";
private final static String START_METHOD = "start.method";
private final static String STOP_CLASS = "stop";
private final static String STOP_METHOD = "stop.method";
private final static String STOP_ARGS = "stop.args";
private String configFileName = null;
private final DaemonConfiguration config;
private final Invoker startup;
private final Invoker shutdown;
public DaemonWrapper()
{
super();
config = new DaemonConfiguration();
startup = new Invoker();
shutdown = new Invoker();
}
/**
* Called from DaemonLoader on init stage.
*
* Accepts the following configuration arguments:
*
* - -daemon-properties: - load DaemonConfiguration properties from the specified file to act as defaults
* - -start: set start class name
* - -start-method: set start method name
* - -stop: set stop class name
* - -stop-method: set stop method name
* - -stop-argument: set optional argument to stop method
* - Anything else is treated as a startup argument
*
*
* The following "-daemon-properties" are recognised:
*
* - args (startup argument)
* - start
* - start.method
* - stop
* - stop.method
* - stop.args
*
* These are used to set the corresponding item if it has not already been
* set by the command arguments. However, note that args and stop.args are
* appended to any existing values.
*/
public void init(DaemonContext context)
throws Exception
{
String[] args = context.getArguments();
if (args != null) {
int i;
// Parse our arguments and remove them
// from the final argument array we are
// passing to our child.
for (i = 0; i < args.length; i++) {
if (args[i].equals("--")) {
// Done with argument processing
break;
}
else if (args[i].equals("-daemon-properties")) {
if (++i == args.length)
throw new IllegalArgumentException(args[i - 1]);
configFileName = args[i];
}
else if (args[i].equals("-start")) {
if (++i == args.length)
throw new IllegalArgumentException(args[i - 1]);
startup.setClassName(args[i]);
}
else if (args[i].equals("-start-method")) {
if (++i == args.length)
throw new IllegalArgumentException(args[i - 1]);
startup.setMethodName(args[i]);
}
else if (args[i].equals("-stop")) {
if (++i == args.length)
throw new IllegalArgumentException(args[i - 1]);
shutdown.setClassName(args[i]);
}
else if (args[i].equals("-stop-method")) {
if (++i == args.length)
throw new IllegalArgumentException(args[i - 1]);
shutdown.setMethodName(args[i]);
}
else if (args[i].equals("-stop-argument")) {
if (++i == args.length)
throw new IllegalArgumentException(args[i - 1]);
String[] aa = new String[1];
aa[0] = args[i];
shutdown.addArguments(aa);
}
else {
// This is not our option.
// Everything else will be forwarded to the main
break;
}
}
if (args.length > i) {
String[] copy = new String[args.length - i];
System.arraycopy(args, i, copy, 0, copy.length);
startup.addArguments(copy);
}
}
if (config.load(configFileName)) {
// Setup params if not set via cmdline.
startup.setClassName(config.getProperty(START_CLASS));
startup.setMethodName(config.getProperty(START_METHOD));
// Merge the config with command line arguments
startup.addArguments(config.getPropertyArray(ARGS));
shutdown.setClassName(config.getProperty(STOP_CLASS));
shutdown.setMethodName(config.getProperty(STOP_METHOD));
shutdown.addArguments(config.getPropertyArray(STOP_ARGS));
}
startup.validate();
shutdown.validate();
}
/**
*/
public void start()
throws Exception
{
startup.invoke();
}
/**
*/
public void stop()
throws Exception
{
shutdown.invoke();
}
/**
*/
public void destroy()
{
// Nothing for the moment
System.err.println("DaemonWrapper: instance " + this.hashCode() + " destroy");
}
// Internal class for wrapping the start/stop methods
class Invoker
{
private String name = null;
private String call = null;
private String[] args = null;
private Method inst = null;
private Class main = null;
protected Invoker()
{
}
protected void setClassName(String name)
{
if (this.name == null)
this.name = name;
}
protected void setMethodName(String name)
{
if (this.call == null)
this.call = name;
}
protected void addArguments(String[] args)
{
if (args != null) {
ArrayList aa = new ArrayList();
if (this.args != null)
aa.addAll(Arrays.asList(this.args));
aa.addAll(Arrays.asList(args));
this.args = (String[])aa.toArray(new String[aa.size()]);
}
}
protected void invoke()
throws Exception
{
if (name.equals("System") && call.equals("exit")) {
// Just call a System.exit()
// The start method was probably installed
// a shutdown hook.
System.exit(0);
}
else {
Object obj = main.newInstance();
Object arg[] = new Object[1];
arg[0] = args;
inst.invoke(obj, arg);
}
}
// Load the class using reflection
protected void validate()
throws Exception
{
/* Check the class name */
if (name == null) {
name = "System";
call = "exit";
return;
}
if (args == null)
args = new String[0];
if (call == null)
call = "main";
// Get the ClassLoader loading this class
ClassLoader cl = DaemonWrapper.class.getClassLoader();
if (cl == null)
throw new NullPointerException("Cannot retrieve ClassLoader instance");
Class[] ca = new Class[1];
ca[0] = args.getClass();
// Find the required class
main = cl.loadClass(name);
if (main == null)
throw new ClassNotFoundException(name);
// Find the required method.
// NoSuchMethodException will be thrown if matching method
// is not found.
inst = main.getMethod(call, ca);
}
}
}