ClassFab


1   // Copyright 2004, 2005 The Apache Software Foundation
2   //
3   // Licensed under the Apache License, Version 2.0 (the "License");
4   // you may not use this file except in compliance with the License.
5   // You may obtain a copy of the License at
6   //
7   //     http://www.apache.org/licenses/LICENSE-2.0
8   //
9   // Unless required by applicable law or agreed to in writing, software
10  // distributed under the License is distributed on an "AS IS" BASIS,
11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12  // See the License for the specific language governing permissions and
13  // limitations under the License.
14  
15  package org.apache.hivemind.service;
16  
17  /**
18   * Used when fabricating a new class.  Represents a wrapper around
19   * the Javassist library.
20   * 
21   * <p>
22   * The core concept of Javassist is how method bodies (as well as constructor bodies, etc.)
23   * are specified ... as a very Java-like scripting language.  The 
24   * {@link org.apache.hivemind.service.BodyBuilder} class is <em>very</em> useful for assembling
25   * this method bodies.  Details are available at the
26   * <a HREF="http://jboss.org/products/javassist">Javassist home page</a>.
27   * 
28   * <p>
29   * Method bodies look largely like Java. References to java classes must be fully qualified.
30   * Several special variables are used:
31   * <ul>
32   * <li><code>$0</code> first parameter, equivalent to <code>this</code> in Java code (and can't
33   * be used when creating a static method)
34   * <li><code>$1, $2, ...</code> actual parameters to the method
35   * <li><code>$args</code> all the parameters as an <code>Object[]</code>
36   * <li><code>$r</code> the return type of the method, typically used as <code>return ($r) ...</code>.
37   * <code>$r</code> is valid with method that return <code>void</code>. This also handles conversions
38   * between wrapper types and primitive types.
39   * <li><code>$w</code> conversion from primitive type to wrapper type, used as <code>($w) foo()</code> where
40   * <code>foo()</code> returns a primitive type and a wrapper type is needed
41   * <li>
42   * </ul>
43   *
44   * @author Howard Lewis Ship
45   */
46  public interface ClassFab
47  {
48      /**
49       * Adds the specified interface as an interface implemented by this class.
50       */
51      public void addInterface(Class   interfaceClass);
52  
53      /**
54       * Adds a new field with the given name and type.  The field is
55       * added as a private field.
56       */
57  
58      public void addField(String   name, Class   type);
59  
60      public boolean canConvert(Class   inputClass);
61      
62      /**
63       * Convenience method for checking whether the fabricated class already contains
64       * a method.
65       * @param signature the signature
66       * @return whether or not the fabricated class already contains the method
67       */
68      public boolean containsMethod( MethodSignature signature );
69      
70      /**
71       * Adds a method.  The method is a public instance method.
72       * @return a method fabricator, used to add catch handlers.
73       * @param modifiers Modifiers for the method (see {@link java.lang.reflect.Modifier}).
74       * @param signature defines the name, return type, parameters and exceptions thrown
75       * @param body The body of the method.
76       * @throws org.apache.hivemind.ApplicationRuntimeException if a method with that signature has already
77       * been added, or if there is a Javassist compilation error
78       */
79  
80      public MethodFab addMethod(int modifiers, MethodSignature signature, String   body);
81  
82      /**
83       * Returns a previous defined method so that it can be further enhanced
84       * (perhaps by adding additional catches, etc.).
85       * 
86       * @param signature the signature of the method previously added
87       * @return the MethodFab for that method, or null if the method has not been added yet
88       */
89  
90      public MethodFab getMethodFab(MethodSignature signature);
91  
92      /**
93       * Adds a constructor to the class.  The constructor will be public.
94       * @param parameterTypes the type of each parameter, or null if the constructor takes no parameters.
95       * @param exceptions the type of each exception, or null if the constructor throws no exceptions.
96       * @param body The body of the constructor.
97       */
98      public void addConstructor(Class  [] parameterTypes, Class  [] exceptions, String   body);
99  
100     /**
101      * Invoked last to create the class.  This will enforce that
102      * all abstract methods have been implemented in the (concrete) class.
103      */
104     public Class   createClass();
105 }
106
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