Jetty example source code file (LazyList.java)

This example Jetty source code file (LazyList.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Jetty tags/keywords

arraylist, arraylist, class, indexoutofboundsexception, io, iterator, lazylist, list, list, listiterator, object, object, reflection, serializable, string, string, util

The Jetty LazyList.java source code

// ========================================================================
// Copyright 2004-2005 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// Licensed 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.
// ========================================================================

package org.mortbay.util;
import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

/* ------------------------------------------------------------ */
/** Lazy List creation.
 * A List helper class that attempts to avoid unneccessary List
 * creation.   If a method needs to create a List to return, but it is
 * expected that this will either be empty or frequently contain a
 * single item, then using LazyList will avoid additional object
 * creations by using Collections.EMPTY_LIST or
 * Collections.singletonList where possible.
 *
 * <p>
Usage
 * <pre>
 *   Object lazylist =null;
 *   while(loopCondition)
 *   {
 *     Object item = getItem();
 *     if (item.isToBeAdded())
 *         lazylist = LazyList.add(lazylist,item);
 *   }
 *   return LazyList.getList(lazylist);
 * </pre>
 *
 * An ArrayList of default size is used as the initial LazyList.
 *
 * @see java.util.List
 * @author Greg Wilkins (gregw)
 */
public class LazyList
    implements Cloneable, Serializable
{
    private static final String[] __EMTPY_STRING_ARRAY = new String[0];
    
    /* ------------------------------------------------------------ */
    private LazyList()
    {}
    
    /* ------------------------------------------------------------ */
    /** Add an item to a LazyList 
     * @param list The list to add to or null if none yet created.
     * @param item The item to add.
     * @return The lazylist created or added to.
     */
    public static Object add(Object list, Object item)
    {
        if (list==null)
        {
            if (item instanceof List || item==null)
            {
                List l = new ArrayList();
                l.add(item);
                return l;
            }

            return item;
        }

        if (list instanceof List)
        {
            ((List)list).add(item);
            return list;
        }

        List l=new ArrayList();
        l.add(list);
        l.add(item);
        return l;    
    }

    /* ------------------------------------------------------------ */
    /** Add an item to a LazyList 
     * @param list The list to add to or null if none yet created.
     * @param index The index to add the item at.
     * @param item The item to add.
     * @return The lazylist created or added to.
     */
    public static Object add(Object list, int index, Object item)
    {
        if (list==null)
        {
            if (index>0 || item instanceof List || item==null)
            {
                List l = new ArrayList();
                l.add(index,item);
                return l;
            }
            return item;
        }

        if (list instanceof List)
        {
            ((List)list).add(index,item);
            return list;
        }

        List l=new ArrayList();
        l.add(list);
        l.add(index,item);
        return l;    
    }
    
    /* ------------------------------------------------------------ */
    /** Add the contents of a Collection to a LazyList
     * @param list The list to add to or null if none yet created.
     * @param collection The Collection whose contents should be added.
     * @return The lazylist created or added to.
     */
    public static Object addCollection(Object list, Collection collection)
    {
        Iterator i=collection.iterator();
        while(i.hasNext())
            list=LazyList.add(list,i.next());
        return list;
    }
    
    /* ------------------------------------------------------------ */
    /** Add the contents of an array to a LazyList
     * @param list The list to add to or null if none yet created.
     * @param collection The Collection whose contents should be added.
     * @return The lazylist created or added to.
     */
    public static Object addArray(Object list, Object[] array)
    {
        for(int i=0;array!=null && i<array.length;i++)
            list=LazyList.add(list,array[i]);
        return list;
    }

    /* ------------------------------------------------------------ */
    /** Ensure the capcity of the underlying list.
     * 
     */
    public static Object ensureSize(Object list, int initialSize)
    {
        if (list==null)
            return new ArrayList(initialSize);
        if (list instanceof ArrayList)
        {
            ArrayList ol=(ArrayList)list;
            if (ol.size()>initialSize)
                return ol;
            ArrayList nl = new ArrayList(initialSize);
            nl.addAll(ol);
            return nl;
        }
        List l= new ArrayList(initialSize);
        l.add(list);
        return l;    
    }

    /* ------------------------------------------------------------ */
    public static Object remove(Object list, Object o)
    {
        if (list==null)
            return null;

        if (list instanceof List)
        {
            List l = (List)list;
            l.remove(o);
            if (l.size()==0)
                return null;
            return list;
        }

        if (list.equals(o))
            return null;
        return list;
    }
    
    /* ------------------------------------------------------------ */
    public static Object remove(Object list, int i)
    {
        if (list==null)
            return null;

        if (list instanceof List)
        {
            List l = (List)list;
            l.remove(i);
            if (l.size()==0)
                return null;
            return list;
        }

        if (i==0)
            return null;
        return list;
    }
    
    
    
    /* ------------------------------------------------------------ */
    /** Get the real List from a LazyList.
     * 
     * @param list A LazyList returned from LazyList.add(Object)
     * @return The List of added items, which may be an EMPTY_LIST
     * or a SingletonList.
     */
    public static List getList(Object list)
    {
        return getList(list,false);
    }
    

    /* ------------------------------------------------------------ */
    /** Get the real List from a LazyList.
     * 
     * @param list A LazyList returned from LazyList.add(Object) or null
     * @param nullForEmpty If true, null is returned instead of an
     * empty list.
     * @return The List of added items, which may be null, an EMPTY_LIST
     * or a SingletonList.
     */
    public static List getList(Object list, boolean nullForEmpty)
    {
        if (list==null)
            return nullForEmpty?null:Collections.EMPTY_LIST;
        if (list instanceof List)
            return (List)list;
        
        List l = new ArrayList(1);
        l.add(list);
        return l;
    }

    
    /* ------------------------------------------------------------ */
    public static String[] toStringArray(Object list)
    {
        if (list==null)
            return __EMTPY_STRING_ARRAY;
        
        if (list instanceof List)
        {
            List l = (List)list;
            String[] a = new String[l.size()];
            for (int i=l.size();i-->0;)
            {
                Object o=l.get(i);
                if (o!=null)
                    a[i]=o.toString();
            }
            return a;
        }
        
        return new String[] {list.toString()};
    }

    /* ------------------------------------------------------------ */
    public static Object toArray(Object list,Class aClass)
    {
        if (list==null)
            return (Object[])Array.newInstance(aClass,0);
        
        if (list instanceof List)
        {
            List l = (List)list;
            if (aClass.isPrimitive())
            {
                Object a = Array.newInstance(aClass,l.size());
                for (int i=0;i<l.size();i++)
                    Array.set(a,i,l.get(i));
                return a;
            }
            return l.toArray((Object[])Array.newInstance(aClass,l.size()));
            
        }
        
        Object a = Array.newInstance(aClass,1);
        Array.set(a,0,list);
        return a;
    }

    /* ------------------------------------------------------------ */
    /** The size of a lazy List 
     * @param list  A LazyList returned from LazyList.add(Object) or null
     * @return the size of the list.
     */
    public static int size(Object list)
    {
        if (list==null)
            return 0;
        if (list instanceof List)
            return ((List)list).size();
        return 1;
    }
    
    /* ------------------------------------------------------------ */
    /** Get item from the list 
     * @param list  A LazyList returned from LazyList.add(Object) or null
     * @param i int index
     * @return the item from the list.
     */
    public static Object get(Object list, int i)
    {
        if (list==null)
            throw new IndexOutOfBoundsException();
        
        if (list instanceof List)
            return ((List)list).get(i);

        if (i==0)
            return list;
        
        throw new IndexOutOfBoundsException();
    }
    
    /* ------------------------------------------------------------ */
    public static boolean contains(Object list,Object item)
    {
        if (list==null)
            return false;
        
        if (list instanceof List)
            return ((List)list).contains(item);

        return list.equals(item);
    }
    

    /* ------------------------------------------------------------ */
    public static Object clone(Object list)
    {
        if (list==null)
            return null;
        if (list instanceof List)
            return new ArrayList((List)list);
        return list;
    }
    
    /* ------------------------------------------------------------ */
    public static String toString(Object list)
    {
        if (list==null)
            return "[]";
        if (list instanceof List)
            return ((List)list).toString();
        return "["+list+"]";
    }

    /* ------------------------------------------------------------ */
    public static Iterator iterator(Object list)
    {
        if (list==null)
            return Collections.EMPTY_LIST.iterator();
        if (list instanceof List)
            return ((List)list).iterator();
        return getList(list).iterator();
    }
    
    /* ------------------------------------------------------------ */
    public static ListIterator listIterator(Object list)
    {
        if (list==null)
            return Collections.EMPTY_LIST.listIterator();
        if (list instanceof List)
            return ((List)list).listIterator();
        return getList(list).listIterator();
    }

    /* ------------------------------------------------------------ */
    /**
     * @param array Any array of object
     * @return A new <i>modifiable list initialised with the elements from array.
     */
    public static List array2List(Object[] array)
    {	
        if (array==null || array.length==0)
            return new ArrayList();
        return new ArrayList(Arrays.asList(array));
    }

    /* ------------------------------------------------------------ */
    /** Add element to an array
     * @param array The array to add to (or null)
     * @param item The item to add
     * @param type The type of the array (in case of null array)
     * @return new array with contents of array plus item
     */
    public static Object[] addToArray(Object[] array, Object item, Class type)
    {
        if (array==null)
        {
            if (type==null && item!=null)
                type= item.getClass();
            Object[] na = (Object[])Array.newInstance(type, 1);
            na[0]=item;
            return na;
        }
        else
        {
            Class c = array.getClass().getComponentType();
            Object[] na = (Object[])Array.newInstance(c, Array.getLength(array)+1);
            System.arraycopy(array, 0, na, 0, array.length);
            na[array.length]=item;
            return na;
        }
    }

    /* ------------------------------------------------------------ */
    public static Object[] removeFromArray(Object[] array, Object item)
    {
        if (item==null || array==null)
            return array;
        for (int i=array.length;i-->0;)
        {
            if (item.equals(array[i]))
            {
                Class c = array==null?item.getClass():array.getClass().getComponentType();
                Object[] na = (Object[])Array.newInstance(c, Array.getLength(array)-1);
                if (i>0)
                    System.arraycopy(array, 0, na, 0, i);
                if (i+1<array.length)
                    System.arraycopy(array, i+1, na, i, array.length-(i+1));
                return na;
            }
        }
        return array;
    }
    
}