contextmap.java

基于Jabber协议的即时消息服务器

/*
 * Copyright (C) The Apache Software Foundation. All rights reserved.
 *
 * This software is published under the terms of the Apache Software License
 * version 1.1, a copy of which has been included with this distribution in
 * the LICENSE file.
 */
package org.jivesoftware.util.log;

import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * The ContextMap contains non-hierarchical context information
 * relevent to a particular LogEvent. It may include information
 * such as;
 * <p/>
 * <ul>
 * <li>user -&gt;fred</li>
 * <li>hostname -&gt;helm.realityforge.org</li>
 * <li>ipaddress -&gt;1.2.3.4</li>
 * <li>interface -&gt;127.0.0.1</li>
 * <li>caller -&gt;com.biz.MyCaller.method(MyCaller.java:18)</li>
 * <li>source -&gt;1.6.3.2:33</li>
 * </ul>
 * The context is bound to a thread (and inherited by sub-threads) but
 * it can also be added to by LogTargets.
 *
 * @author <a href="mailto:[e-mail]">Peter Donald</a>
 */
public final class ContextMap implements Serializable {
    ///Thread local for holding instance of map associated with current thread
    private static final ThreadLocal c_context = new InheritableThreadLocal();

    private final ContextMap m_parent;

    ///Container to hold map of elements
    private Map m_map = Collections.synchronizedMap(new HashMap());

    ///Flag indicating whether this map should be readonly
    private transient boolean m_readOnly;

    /**
     * Get the Current ContextMap.
     * This method returns a ContextMap associated with current thread. If the
     * thread doesn't have a ContextMap associated with it then a new
     * ContextMap is created.
     *
     * @return the current ContextMap
     */
    public final static ContextMap getCurrentContext() {
        return getCurrentContext(true);
    }

    /**
     * Get the Current ContextMap.
     * This method returns a ContextMap associated with current thread.
     * If the thread doesn't have a ContextMap associated with it and
     * autocreate is true then a new ContextMap is created.
     *
     * @param autocreate true if a ContextMap is to be created if it doesn't exist
     * @return the current ContextMap
     */
    public final static ContextMap getCurrentContext(final boolean autocreate) {
        //Check security permission here???
        ContextMap context = (ContextMap)c_context.get();

        if (null == context && autocreate) {
            context = new ContextMap();
            c_context.set(context);
        }

        return context;
    }

    /**
     * Bind a particular ContextMap to current thread.
     *
     * @param context the context map (may be null)
     */
    public final static void bind(final ContextMap context) {
        //Check security permission here??
        c_context.set(context);
    }

    /**
     * Default constructor.
     */
    public ContextMap() {
        this(null);
    }

    /**
     * Constructor that sets parent contextMap.
     *
     * @param parent the parent ContextMap
     */
    public ContextMap(final ContextMap parent) {
        m_parent = parent;
    }

    /**
     * Make the context read-only.
     * This makes it safe to allow untrusted code reference
     * to ContextMap.
     */
    public void makeReadOnly() {
        m_readOnly = true;
    }

    /**
     * Determine if context is read-only.
     *
     * @return true if Context is read only, false otherwise
     */
    public boolean isReadOnly() {
        return m_readOnly;
    }

    /**
     * Empty the context map.
     */
    public void clear() {
        checkReadable();

        m_map.clear();
    }

    /**
     * Get an entry from the context.
     *
     * @param key           the key to map
     * @param defaultObject a default object to return if key does not exist
     * @return the object in context
     */
    public Object get(final String key, final Object defaultObject) {
        final Object object = get(key);

        if (null != object)
            return object;
        else
            return defaultObject;
    }

    /**
     * Get an entry from the context.
     *
     * @param key the key to map
     * @return the object in context or null if none with specified key
     */
    public Object get(final String key) {
        final Object result = m_map.get(key);

        if (null == result && null != m_parent) {
            return m_parent.get(key);
        }

        return result;
    }

    /**
     * Set a value in context
     *
     * @param key   the key
     * @param value the value (may be null)
     */
    public void set(final String key, final Object value) {
        checkReadable();

        if (value == null) {
            m_map.remove(key);
        }
        else {
            m_map.put(key, value);
        }
    }


    /**
     * Get the number of contexts in map.
     *
     * @return the number of contexts in map
     */
    public int getSize() {
        return m_map.size();
    }

    /**
     * Helper method that sets context to read-only after de-serialization.
     *
     * @return the corrected object version
     * @throws ObjectStreamException if an error occurs
     */
    private Object readResolve() throws ObjectStreamException {
        makeReadOnly();
        return this;
    }

    /**
     * Utility method to verify that Context is read-only.
     */
    private void checkReadable() {
        if (isReadOnly()) {
            throw new IllegalStateException("ContextMap is read only and can not be modified");
        }
    }
}