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1   package groovy.lang;
2   
3   import org.codehaus.groovy.runtime.InvokerHelper;
4   
5   import java.beans.IntrospectionException;
6   
7   /***
8    * As subclass of MetaClass, ProxyMetaClass manages calls from Groovy Objects to POJOs.
9    * It enriches MetaClass with the feature of making method invokations interceptable by
10   * an Interceptor. To this end, it acts as a decorator (decorator pattern) allowing
11   * to add or withdraw this feature at runtime.
12   * See groovy/lang/InterceptorTest.groovy for details.
13   * @author Dierk Koenig
14   */
15  public class ProxyMetaClass extends MetaClass {
16  
17      protected MetaClass adaptee = null;
18      protected Interceptor interceptor = null;
19  
20      /***
21       * convenience factory method for the most usual case.
22       */
23      public static ProxyMetaClass getInstance(Class theClass) throws IntrospectionException {
24          MetaClassRegistry metaRegistry = InvokerHelper.getInstance().getMetaRegistry();
25          MetaClass meta = metaRegistry.getMetaClass(theClass);
26          return new ProxyMetaClass(metaRegistry, theClass, meta);
27      }
28      /***
29       * @param adaptee   the MetaClass to decorate with interceptability
30       */
31      public ProxyMetaClass(MetaClassRegistry registry, Class theClass, MetaClass adaptee) throws IntrospectionException {
32          super(registry, theClass);
33          this.adaptee = adaptee;
34          if (null == adaptee) throw new IllegalArgumentException("adaptee must not be null");
35      }
36  
37      /***
38       * Use the ProxyMetaClass for the given Closure.
39       * Cares for balanced register/unregister.
40       * @param closure piece of code to be executed with registered ProxyMetaClass
41       */
42      public void use(Closure closure){
43          registry.setMetaClass(theClass, this);
44          closure.call();
45          registry.setMetaClass(theClass, adaptee);
46      }
47  
48       /***
49       * Use the ProxyMetaClass for the given Closure.
50       * Cares for balanced setting/unsetting ProxyMetaClass.
51       * @param closure piece of code to be executed with ProxyMetaClass
52       */
53      public void use(GroovyObject object, Closure closure){
54          object.setMetaClass(this);
55          closure.call();
56          object.setMetaClass(adaptee);
57      }
58  
59      /***
60       * @return the interceptor in use or null if no interceptor is used
61       */
62      public Interceptor getInterceptor() {
63          return interceptor;
64      }
65  
66      /***
67       * @param interceptor may be null to reset any interception
68       */
69      public void setInterceptor(Interceptor interceptor) {
70          this.interceptor = interceptor;
71      }
72  
73      /***
74       * Call invokeMethod on adaptee with logic like in MetaClass unless we have an Interceptor.
75       * With Interceptor the call is nested in its beforeInvoke and afterInvoke methods.
76       * The method call is suppressed if Interceptor.doInvoke() returns false.
77       * See Interceptor for details.
78       */
79      public Object invokeMethod(final Object object, final String methodName, final Object[] arguments) {
80          return doCall(object, methodName, arguments, new Callable(){
81              public Object call() {
82                  return adaptee.invokeMethod(object, methodName, arguments);
83              }
84          });
85      }
86      /***
87       * Call invokeStaticMethod on adaptee with logic like in MetaClass unless we have an Interceptor.
88       * With Interceptor the call is nested in its beforeInvoke and afterInvoke methods.
89       * The method call is suppressed if Interceptor.doInvoke() returns false.
90       * See Interceptor for details.
91       */
92      public Object invokeStaticMethod(final Object object, final String methodName, final Object[] arguments) {
93          return doCall(object, methodName, arguments, new Callable(){
94              public Object call() {
95                  return adaptee.invokeStaticMethod(object, methodName, arguments);
96              }
97          });
98      }
99  
100     /***
101      * Call invokeConstructor on adaptee with logic like in MetaClass unless we have an Interceptor.
102      * With Interceptor the call is nested in its beforeInvoke and afterInvoke methods.
103      * The method call is suppressed if Interceptor.doInvoke() returns false.
104      * See Interceptor for details.
105      */
106     public Object invokeConstructor(final Object[] arguments) {
107         return doCall(theClass, "ctor", arguments, new Callable(){
108             public Object call() {
109                 return adaptee.invokeConstructor(arguments);
110             }
111         });
112     }
113 
114     // since Java has no Closures...
115     private interface Callable{
116         Object call();
117     }
118     private Object doCall(Object object, String methodName, Object[] arguments, Callable howToInvoke) {
119         if (null == interceptor) {
120             return howToInvoke.call();
121         }
122         Object result = interceptor.beforeInvoke(object, methodName, arguments);
123         if (interceptor.doInvoke()) {
124             result = howToInvoke.call();
125         }
126         result = interceptor.afterInvoke(object, methodName, arguments, result);
127         return result;
128     }
129 }