TargetSource


1   /*<
2    * Copyright 2002-2007 the original author or authors.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package org.springframework.aop;
18  
19  /**
20   * A <code>TargetSource</code> is used to obtain the current "target" of
21   * an AOP invocation, which will be invoked via reflection if no around
22   * advice chooses to end the interceptor chain itself.
23   *
24   * <p>If a <code>TargetSource</code> is "static", it will always return
25   * the same target, allowing optimizations in the AOP framework. Dynamic
26   * target sources can support pooling, hot swapping, etc.
27   *
28   * <p>Application developers don't usually need to work with
29   * <code>TargetSources</code> directly: this is an AOP framework interface.
30   *
31   * @author Rod Johnson
32   */
33  public interface TargetSource extends TargetClassAware {
34  
35      /**
36       * Return the type of targets returned by this {@link TargetSource}.
37       * <p>Can return <code>null</code>, although certain usages of a
38       * <code>TargetSource</code> might just work with a predetermined
39       * target class.
40       * @return the type of targets returned by this {@link TargetSource}
41       */
42      Class   getTargetClass();
43  
44      /**
45       * Will all calls to {@link #getTarget()} return the same object?
46       * <p>In that case, there will be no need to invoke
47       * {@link #releaseTarget(Object)}, and the AOP framework can cache
48       * the return value of {@link #getTarget()}.
49       * @return <code>true</code> if the target is immutable
50       * @see #getTarget
51       */
52      boolean isStatic();
53  
54      /**
55       * Return a target instance. Invoked immediately before the
56       * AOP framework calls the "target" of an AOP method invocation.
57       * @return the target object, which contains the joinpoint
58       * @throws Exception if the target object can't be resolved
59       */
60      Object   getTarget() throws Exception  ;
61  
62      /**
63       * Release the given target object obtained from the
64       * {@link #getTarget()} method.
65       * @param target object obtained from a call to {@link #getTarget()}
66       * @throws Exception if the object can't be released
67       */
68      void releaseTarget(Object   target) throws Exception  ;
69  
70  }
71
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