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Java > Open Source Codes > org > objectstyle > cayenne > util > PropertyComparator


1 /* ====================================================================
2  *
3  * The ObjectStyle Group Software License, version 1.1
4  * ObjectStyle Group - http://objectstyle.org/
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6  * Copyright (c) 2002-2005, Andrei (Andrus) Adamchik and individual authors
7  * of the software. All rights reserved.
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10  * modification, are permitted provided that the following conditions
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24  * and hosted on ObjectStyle Group web site (http://objectstyle.org/)."
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54  * <http://objectstyle.org/>.
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56 package org.objectstyle.cayenne.util;
57
58 import java.lang.reflect.InvocationTargetException JavaDoc;
59 import java.lang.reflect.Method JavaDoc;
60 import java.util.Comparator JavaDoc;
61
62 import org.objectstyle.cayenne.CayenneRuntimeException;
63
64 /**
65  * Comparator that can compare Java beans based on a
66  * value of a property. Bean property must be readable
67  * and its type must be an instance of Comparable.
68  *
69  * @author Andrei Adamchik
70  */
71 public class PropertyComparator implements Comparator JavaDoc {
72     protected Method JavaDoc getter;
73     protected boolean ascending;
74
75     public static String JavaDoc capitalize(String JavaDoc s) {
76         if (s.length() == 0) {
77             return s;
78         }
79         char chars[] = s.toCharArray();
80         chars[0] = Character.toUpperCase(chars[0]);
81         return new String JavaDoc(chars);
82     }
83
84     public static Method JavaDoc findReadMethod(String JavaDoc propertyName, Class JavaDoc beanClass) {
85         String JavaDoc base = capitalize(propertyName);
86
87         // find non-boolean property
88 try {
89             return beanClass.getMethod("get" + base, null);
90         }
91         catch (Exception JavaDoc ex) {
92             // ignore, this might be a boolean property
93 }
94
95         try {
96             return beanClass.getMethod("is" + base, null);
97         }
98         catch (Exception JavaDoc ex) {
99             // ran out of options
100 return null;
101         }
102     }
103
104     /**
105      * Method to read a simple one-step property of a JavaBean.
106      */
107     public static Object JavaDoc readProperty(String JavaDoc propertyName, Object JavaDoc bean)
108         throws NoSuchMethodException JavaDoc, IllegalAccessException JavaDoc, InvocationTargetException JavaDoc {
109         if (bean == null) {
110             throw new NullPointerException JavaDoc("Null bean. Property: " + propertyName);
111         }
112
113         Method JavaDoc getter = findReadMethod(propertyName, bean.getClass());
114
115         if (getter == null) {
116             throw new NoSuchMethodException JavaDoc(
117                 "No such property '"
118                     + propertyName
119                     + "' in class "
120                     + bean.getClass().getName());
121         }
122
123         return getter.invoke(bean, null);
124     }
125
126     public PropertyComparator(String JavaDoc propertyName, Class JavaDoc beanClass) {
127         this(propertyName, beanClass, true);
128     }
129
130     public PropertyComparator(String JavaDoc propertyName, Class JavaDoc beanClass, boolean ascending) {
131         getter = findReadMethod(propertyName, beanClass);
132         if (getter == null) {
133             throw new CayenneRuntimeException("No getter for " + propertyName);
134         }
135
136         this.ascending = ascending;
137     }
138
139     /**
140      * @see java.util.Comparator#compare(Object, Object)
141      */
142     public int compare(Object JavaDoc o1, Object JavaDoc o2) {
143         return (ascending) ? compareAsc(o1, o2) : compareAsc(o2, o1);
144     }
145
146     protected int compareAsc(Object JavaDoc o1, Object JavaDoc o2) {
147
148         if ((o1 == null && o2 == null) || o1 == o2) {
149             return 0;
150         }
151         else if (o1 == null && o2 != null) {
152             return -1;
153         }
154         else if (o1 != null && o2 == null) {
155             return 1;
156         }
157
158         try {
159             Comparable JavaDoc p1 = (Comparable JavaDoc) getter.invoke(o1, null);
160             Comparable JavaDoc p2 = (Comparable JavaDoc) getter.invoke(o2, null);
161
162             return (p1 == null) ? -1 : p1.compareTo(p2);
163         }
164         catch (Exception JavaDoc ex) {
165             throw new CayenneRuntimeException("Error reading property.", ex);
166         }
167     }
168 }
169
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