| // |
| // ======================================================================== |
| // Copyright (c) 1995-2017 Mort Bay Consulting Pty. Ltd. |
| // ------------------------------------------------------------------------ |
| // All rights reserved. This program and the accompanying materials |
| // are made available under the terms of the Eclipse Public License v1.0 |
| // and Apache License v2.0 which accompanies this distribution. |
| // |
| // The Eclipse Public License is available at |
| // http://www.eclipse.org/legal/epl-v10.html |
| // |
| // The Apache License v2.0 is available at |
| // http://www.opensource.org/licenses/apache2.0.php |
| // |
| // You may elect to redistribute this code under either of these licenses. |
| // ======================================================================== |
| // |
| |
| package org.eclipse.jetty.util; |
| |
| import java.io.Serializable; |
| import java.lang.reflect.Array; |
| import java.util.ArrayList; |
| 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 unnecessary 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 {@link Collections#EMPTY_LIST} or |
| * {@link Collections#singletonList(Object)} where possible. |
| * <p> |
| * LazyList works by passing an opaque representation of the list in |
| * and out of all the LazyList methods. This opaque object is either |
| * null for an empty list, an Object for a list with a single entry |
| * or an {@link ArrayList} for a list of items. |
| * |
| * <p><h4>Usage</h4> |
| * <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 |
| */ |
| @SuppressWarnings("serial") |
| 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. |
| */ |
| @SuppressWarnings("unchecked") |
| public static Object add(Object list, Object item) |
| { |
| if (list==null) |
| { |
| if (item instanceof List || item==null) |
| { |
| List<Object> l = new ArrayList<Object>(); |
| l.add(item); |
| return l; |
| } |
| |
| return item; |
| } |
| |
| if (list instanceof List) |
| { |
| ((List<Object>)list).add(item); |
| return list; |
| } |
| |
| List<Object> l=new ArrayList<Object>(); |
| 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. |
| */ |
| @SuppressWarnings("unchecked") |
| public static Object add(Object list, int index, Object item) |
| { |
| if (list==null) |
| { |
| if (index>0 || item instanceof List || item==null) |
| { |
| List<Object> l = new ArrayList<Object>(); |
| l.add(index,item); |
| return l; |
| } |
| return item; |
| } |
| |
| if (list instanceof List) |
| { |
| ((List<Object>)list).add(index,item); |
| return list; |
| } |
| |
| List<Object> l=new ArrayList<Object>(); |
| 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 array The array 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 capacity of the underlying list. |
| * |
| */ |
| public static Object ensureSize(Object list, int initialSize) |
| { |
| if (list==null) |
| return new ArrayList<Object>(initialSize); |
| if (list instanceof ArrayList) |
| { |
| ArrayList<?> ol=(ArrayList<?>)list; |
| if (ol.size()>initialSize) |
| return ol; |
| ArrayList<Object> nl = new ArrayList<Object>(initialSize); |
| nl.addAll(ol); |
| return nl; |
| } |
| List<Object> l= new ArrayList<Object>(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<E> List<E> 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. |
| */ |
| @SuppressWarnings("unchecked") |
| public static<E> List<E> getList(Object list, boolean nullForEmpty) |
| { |
| if (list==null) |
| { |
| if (nullForEmpty) |
| return null; |
| return Collections.emptyList(); |
| } |
| if (list instanceof List) |
| return (List<E>)list; |
| |
| return (List<E>)Collections.singletonList(list); |
| } |
| |
| /** |
| * Simple utility method to test if List has at least 1 entry. |
| * |
| * @param list |
| * a LazyList, {@link List} or {@link Object} |
| * @return true if not-null and is not empty |
| */ |
| public static boolean hasEntry(Object list) |
| { |
| if (list == null) |
| return false; |
| if (list instanceof List) |
| return !((List<?>)list).isEmpty(); |
| return true; |
| } |
| |
| /** |
| * Simple utility method to test if List is empty |
| * |
| * @param list |
| * a LazyList, {@link List} or {@link Object} |
| * @return true if null or is empty |
| */ |
| public static boolean isEmpty(Object list) |
| { |
| if (list == null) |
| return true; |
| if (list instanceof List) |
| return ((List<?>)list).isEmpty(); |
| return false; |
| } |
| |
| |
| /* ------------------------------------------------------------ */ |
| 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()}; |
| } |
| |
| /* ------------------------------------------------------------ */ |
| /** Convert a lazylist to an array |
| * @param list The list to convert |
| * @param clazz The class of the array, which may be a primitive type |
| * @return array of the lazylist entries passed in |
| */ |
| public static Object toArray(Object list,Class<?> clazz) |
| { |
| if (list==null) |
| return Array.newInstance(clazz,0); |
| |
| if (list instanceof List) |
| { |
| List<?> l = (List<?>)list; |
| if (clazz.isPrimitive()) |
| { |
| Object a = Array.newInstance(clazz,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(clazz,l.size())); |
| |
| } |
| |
| Object a = Array.newInstance(clazz,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. |
| */ |
| @SuppressWarnings("unchecked") |
| public static <E> E get(Object list, int i) |
| { |
| if (list==null) |
| throw new IndexOutOfBoundsException(); |
| |
| if (list instanceof List) |
| return (E)((List<?>)list).get(i); |
| |
| if (i==0) |
| return (E)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<Object>((List<?>)list); |
| return list; |
| } |
| |
| /* ------------------------------------------------------------ */ |
| public static String toString(Object list) |
| { |
| if (list==null) |
| return "[]"; |
| if (list instanceof List) |
| return list.toString(); |
| return "["+list+"]"; |
| } |
| |
| /* ------------------------------------------------------------ */ |
| @SuppressWarnings("unchecked") |
| public static<E> Iterator<E> iterator(Object list) |
| { |
| if (list==null) |
| { |
| List<E> empty=Collections.emptyList(); |
| return empty.iterator(); |
| } |
| if (list instanceof List) |
| { |
| return ((List<E>)list).iterator(); |
| } |
| List<E> l=getList(list); |
| return l.iterator(); |
| } |
| |
| /* ------------------------------------------------------------ */ |
| @SuppressWarnings("unchecked") |
| public static<E> ListIterator<E> listIterator(Object list) |
| { |
| if (list==null) |
| { |
| List<E> empty=Collections.emptyList(); |
| return empty.listIterator(); |
| } |
| if (list instanceof List) |
| return ((List<E>)list).listIterator(); |
| |
| List<E> l=getList(list); |
| return l.listIterator(); |
| } |
| |
| } |
| |