lrumap.java

iBATIS似乎已远离众说纷纭的OR框架之列

        moveToMRU((LinkEntry) entry);  // handles modCount
        entry.setValue(newValue);
    }
    
    /**
     * Adds a new key-value mapping into this map.
     * <p>
     * This implementation checks the LRU size and determines whether to
     * discard an entry or not using {@link #removeLRU(AbstractLinkedMap.LinkEntry)}.
     * <p>
     * From Commons Collections 3.1 this method uses {@link #isFull()} rather
     * than accessing <code>size</code> and <code>maxSize</code> directly.
     * It also handles the scanUntilRemovable functionality.
     * 
     * @param hashIndex  the index into the data array to store at
     * @param hashCode  the hash code of the key to add
     * @param key  the key to add
     * @param value  the value to add
     */
    protected void addMapping(int hashIndex, int hashCode, Object key, Object value) {
        if (isFull()) {
            LinkEntry reuse = header.after;
            boolean removeLRUEntry = false;
            if (scanUntilRemovable) {
                while (reuse != header && reuse != null) {
                    if (removeLRU(reuse)) {
                        removeLRUEntry = true;
                        break;
                    }
                    reuse = reuse.after;
                }
                if (reuse == null) {
                    throw new IllegalStateException(
                        "Entry.after=null, header.after" + header.after + " header.before" + header.before +
                        " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                        " Please check that your keys are immutable, and that you have used synchronization properly." +
                        " If so, then please report this to [e-mail] as a bug.");
                }
            } else {
                removeLRUEntry = removeLRU(reuse);
            }
            
            if (removeLRUEntry) {
                if (reuse == null) {
                    throw new IllegalStateException(
                        "reuse=null, header.after=" + header.after + " header.before" + header.before +
                        " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                        " Please check that your keys are immutable, and that you have used synchronization properly." +
                        " If so, then please report this to [e-mail] as a bug.");
                }
                reuseMapping(reuse, hashIndex, hashCode, key, value);
            } else {
                super.addMapping(hashIndex, hashCode, key, value);
            }
        } else {
            super.addMapping(hashIndex, hashCode, key, value);
        }
    }
    
    /**
     * Reuses an entry by removing it and moving it to a new place in the map.
     * <p>
     * This method uses {@link #removeEntry}, {@link #reuseEntry} and {@link #addEntry}.
     * 
     * @param entry  the entry to reuse
     * @param hashIndex  the index into the data array to store at
     * @param hashCode  the hash code of the key to add
     * @param key  the key to add
     * @param value  the value to add
     */
    protected void reuseMapping(LinkEntry entry, int hashIndex, int hashCode, Object key, Object value) {
        // find the entry before the entry specified in the hash table
        // remember that the parameters (except the first) refer to the new entry,
        // not the old one
        try {
            int removeIndex = hashIndex(entry.hashCode, data.length);
            HashEntry[] tmp = data;  // may protect against some sync issues
            HashEntry loop = tmp[removeIndex];
            HashEntry previous = null;
            while (loop != entry && loop != null) {
                previous = loop;
                loop = loop.next;
            }
            if (loop == null) {
                throw new IllegalStateException(
                    "Entry.next=null, data[removeIndex]=" + data[removeIndex] + " previous=" + previous +
                    " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                    " Please check that your keys are immutable, and that you have used synchronization properly." +
                    " If so, then please report this to [e-mail] as a bug.");
            }
            
            // reuse the entry
            modCount++;
            removeEntry(entry, removeIndex, previous);
            reuseEntry(entry, hashIndex, hashCode, key, value);
            addEntry(entry, hashIndex);
        } catch (NullPointerException ex) {
            throw new IllegalStateException(
                    "NPE, entry=" + entry + " entryIsHeader=" + (entry==header) +
                    " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                    " Please check that your keys are immutable, and that you have used synchronization properly." +
                    " If so, then please report this to [e-mail] as a bug.");
        }
    }
    
    /**
     * Subclass method to control removal of the least recently used entry from the map.
     * <p>
     * This method exists for subclasses to override. A subclass may wish to
     * provide cleanup of resources when an entry is removed. For example:
     * <pre>
     * protected boolean removeLRU(LinkEntry entry) {
     *   releaseResources(entry.getValue());  // release resources held by entry
     *   return true;  // actually delete entry
     * }
     * </pre>
     * <p>
     * Alternatively, a subclass may choose to not remove the entry or selectively
     * keep certain LRU entries. For example:
     * <pre>
     * protected boolean removeLRU(LinkEntry entry) {
     *   if (entry.getKey().toString().startsWith("System.")) {
     *     return false;  // entry not removed from LRUMap
     *   } else {
     *     return true;  // actually delete entry
     *   }
     * }
     * </pre>
     * The effect of returning false is dependent on the scanUntilRemovable flag.
     * If the flag is true, the next LRU entry will be passed to this method and so on
     * until one returns false and is removed, or every entry in the map has been passed.
     * If the scanUntilRemovable flag is false, the map will exceed the maximum size.
     * <p>
     * NOTE: Commons Collections 3.0 passed the wrong entry to this method.
     * This is fixed in version 3.1 onwards.
     * 
     * @param entry  the entry to be removed
     */
    protected boolean removeLRU(LinkEntry entry) {
        return true;
    }

    //-----------------------------------------------------------------------
    /**
     * Returns true if this map is full and no new mappings can be added.
     *
     * @return <code>true</code> if the map is full
     */
    public boolean isFull() {
        return (size >= maxSize);
    }

    /**
     * Gets the maximum size of the map (the bound).
     *
     * @return the maximum number of elements the map can hold
     */
    public int maxSize() {
        return maxSize;
    }

    /**
     * Whether this LRUMap will scan until a removable entry is found when the
     * map is full.
     *
     * @return true if this map scans
     * @since Commons Collections 3.1
     */
    public boolean isScanUntilRemovable() {
        return scanUntilRemovable;
    }

    //-----------------------------------------------------------------------
    /**
     * Clones the map without cloning the keys or values.
     *
     * @return a shallow clone
     */
    public Object clone() {
        return super.clone();
    }
    
    /**
     * Write the map out using a custom routine.
     */
    private void writeObject(ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        doWriteObject(out);
    }

    /**
     * Read the map in using a custom routine.
     */
    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        doReadObject(in);
    }
    
    /**
     * Writes the data necessary for <code>put()</code> to work in deserialization.
     */
    protected void doWriteObject(ObjectOutputStream out) throws IOException {
        out.writeInt(maxSize);
        super.doWriteObject(out);
    }

    /**
     * Reads the data necessary for <code>put()</code> to work in the superclass.
     */
    protected void doReadObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        maxSize = in.readInt();
        super.doReadObject(in);
    }
    
}