summaryrefslogtreecommitdiffstats
path: root/src/main/javassist/reflect/Metaobject.java
blob: 8c3749aae9ec17c6c73276888edbf34a7d77c4ea (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999-2005 Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package javassist.reflect;

import java.lang.reflect.Method;
import java.io.Serializable;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

/**
 * A runtime metaobject.
 *
 * <p>A <code>Metaobject</code> is created for
 * every object at the base level.  A different reflective object is
 * associated with a different metaobject.
 *
 * <p>The metaobject intercepts method calls
 * on the reflective object at the base-level.  To change the behavior
 * of the method calls, a subclass of <code>Metaobject</code>
 * should be defined.
 *
 * <p>To obtain a metaobject, calls <code>_getMetaobject()</code>
 * on a reflective object.  For example,
 *
 * <ul><pre>Metaobject m = ((Metalevel)reflectiveObject)._getMetaobject();
 * </pre></ul>
 *
 * @see javassist.reflect.ClassMetaobject
 * @see javassist.reflect.Metalevel
 */
public class Metaobject implements Serializable {
    protected ClassMetaobject classmetaobject;
    protected Metalevel baseobject;
    protected Method[] methods;

    /**
     * Constructs a <code>Metaobject</code>.  The metaobject is
     * constructed before the constructor is called on the base-level
     * object.
     *
     * @param self      the object that this metaobject is associated with.
     * @param args      the parameters passed to the constructor of
     *                  <code>self</code>.
     */
    public Metaobject(Object self, Object[] args) {
        baseobject = (Metalevel)self;
        classmetaobject = baseobject._getClass();
        methods = classmetaobject.getReflectiveMethods();
    }

    /**
     * Constructs a <code>Metaobject</code> without initialization.
     * If calling this constructor, a subclass should be responsible
     * for initialization.
     */
    protected Metaobject() {
        baseobject = null;
        classmetaobject = null;
        methods = null;
    }

    private void writeObject(ObjectOutputStream out) throws IOException {
        out.writeObject(baseobject);
    }

    private void readObject(ObjectInputStream in)
        throws IOException, ClassNotFoundException
    {
        baseobject = (Metalevel)in.readObject();
        classmetaobject = baseobject._getClass();
        methods = classmetaobject.getReflectiveMethods();
    }

    /**
     * Obtains the class metaobject associated with this metaobject.
     *
     * @see javassist.reflect.ClassMetaobject
     */
    public final ClassMetaobject getClassMetaobject() {
        return classmetaobject;
    }

    /**
     * Obtains the object controlled by this metaobject.
     */
    public final Object getObject() {
        return baseobject;
    }

    /**
     * Changes the object controlled by this metaobject.
     *
     * @param self      the object
     */
    public final void setObject(Object self) {
        baseobject = (Metalevel)self;
        classmetaobject = baseobject._getClass();
        methods = classmetaobject.getReflectiveMethods();

        // call _setMetaobject() after the metaobject is settled.
        baseobject._setMetaobject(this);
    }

    /**
     * Returns the name of the method specified
     * by <code>identifier</code>.
     */
    public final String getMethodName(int identifier) {
        String mname = methods[identifier].getName();
        int j = ClassMetaobject.methodPrefixLen;
        for (;;) {
            char c = mname.charAt(j++);
            if (c < '0' || '9' < c)
                break;
        }

        return mname.substring(j);
    }

    /**
     * Returns an array of <code>Class</code> objects representing the
     * formal parameter types of the method specified
     * by <code>identifier</code>.
     */
    public final Class[] getParameterTypes(int identifier) {
        return methods[identifier].getParameterTypes();
    }

    /**
     * Returns a <code>Class</code> objects representing the
     * return type of the method specified by <code>identifier</code>.
     */
    public final Class getReturnType(int identifier) {
        return methods[identifier].getReturnType();
    }

    /**
     * Is invoked when public fields of the base-level
     * class are read and the runtime system intercepts it.
     * This method simply returns the value of the field.
     *
     * <p>Every subclass of this class should redefine this method.
     */
    public Object trapFieldRead(String name) {
        Class jc = getClassMetaobject().getJavaClass();
        try {
            return jc.getField(name).get(getObject());
        }
        catch (NoSuchFieldException e) {
            throw new RuntimeException(e.toString());
        }
        catch (IllegalAccessException e) {
            throw new RuntimeException(e.toString());
        }
    }

    /**
     * Is invoked when public fields of the base-level
     * class are modified and the runtime system intercepts it.
     * This method simply sets the field to the given value.
     *
     * <p>Every subclass of this class should redefine this method.
     */
    public void trapFieldWrite(String name, Object value) {
        Class jc = getClassMetaobject().getJavaClass();
        try {
            jc.getField(name).set(getObject(), value);
        }
        catch (NoSuchFieldException e) {
            throw new RuntimeException(e.toString());
        }
        catch (IllegalAccessException e) {
            throw new RuntimeException(e.toString());
        }
    }

    /**
     * Is invoked when base-level method invocation is intercepted.
     * This method simply executes the intercepted method invocation
     * with the original parameters and returns the resulting value.
     *
     * <p>Every subclass of this class should redefine this method.
     *
     * <p>Note: this method is not invoked if the base-level method
     * is invoked by a constructor in the super class.  For example,
     *
     * <ul><pre>abstract class A {
     *   abstract void initialize();
     *   A() {
     *       initialize();    // not intercepted
     *   }
     * }
     *
     * class B extends A {
     *   void initialize() { System.out.println("initialize()"); }
     *   B() {
     *       super();
     *       initialize();    // intercepted
     *   }
     * }</pre></ul>
     *
     * <p>if an instance of B is created,
     * the invocation of initialize() in B is intercepted only once.
     * The first invocation by the constructor in A is not intercepted.
     * This is because the link between a base-level object and a
     * metaobject is not created until the execution of a
     * constructor of the super class finishes.
     */
    public Object trapMethodcall(int identifier, Object[] args) 
        throws Throwable
    {
        try {
            return methods[identifier].invoke(getObject(), args);
        }
        catch (java.lang.reflect.InvocationTargetException e) {
            throw e.getTargetException();
        }
        catch (java.lang.IllegalAccessException e) {
            throw new CannotInvokeException(e);
        }
    }
}