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1   package org.apache.commons.ognl.enhance;
2   
3   /*
4    * Licensed to the Apache Software Foundation (ASF) under one
5    * or more contributor license agreements.  See the NOTICE file
6    * distributed with this work for additional information
7    * regarding copyright ownership.  The ASF licenses this file
8    * to you under the Apache License, Version 2.0 (the
9    * "License"); you may not use this file except in compliance
10   * with the License.  You may obtain a copy of the License at
11   *
12   *   http://www.apache.org/licenses/LICENSE-2.0
13   *
14   * Unless required by applicable law or agreed to in writing,
15   * software distributed under the License is distributed on an
16   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17   * KIND, either express or implied.  See the License for the
18   * specific language governing permissions and limitations
19   * under the License.
20   */
21  
22  import org.apache.commons.ognl.Node;
23  import org.apache.commons.ognl.OgnlContext;
24  
25  import java.lang.reflect.Method;
26  
27  /**
28   * Core interface implemented by expression compiler instances.
29   */
30  public interface OgnlExpressionCompiler
31  {
32  
33      /** Static constant used in conjunction with {@link OgnlContext} to store temporary references. */
34      String ROOT_TYPE = "-ognl-root-type";
35  
36      /**
37       * The core method executed to compile a specific expression. It is expected that this expression always return a
38       * {@link Node} with a non null {@link org.apache.commons.ognl.Node#getAccessor()} instance - unless an exception is
39       * thrown by the method or the statement wasn't compilable in this instance because of missing/null objects in the
40       * expression. These instances may in some cases continue to call this compilation method until the expression is
41       * resolvable.
42       * 
43       * @param context The context of execution.
44       * @param expression The pre-parsed root expression node to compile.
45       * @param root The root object for the expression - may be null in many instances so some implementations may exit
46       * @throws Exception If an error occurs compiling the expression and no strategy has been implemented to handle
47       *             incremental expression compilation for incomplete expression members.
48       */
49      void compileExpression( OgnlContext context, Node expression, Object root )
50          throws Exception;
51  
52      /**
53       * Gets a javassist safe class string for the given class instance. This is especially useful for handling array vs.
54       * normal class casting strings.
55       * 
56       * @param clazz The class to get a string equivalent javassist compatible string reference for.
57       * @return The string equivalent of the class.
58       */
59      String getClassName( Class<?> clazz );
60  
61      /**
62       * Used in places where the preferred {@link #getSuperOrInterfaceClass(java.lang.reflect.Method, Class)} isn't
63       * possible because the method isn't known for a class. Attempts to upcast the given class to the next available
64       * non-private accessible class so that compiled expressions can reference the interface class of an instance so as
65       * not to be compiled in to overly specific statements.
66       * 
67       * @param clazz The class to attempt to find a compatible interface for.
68       * @return The same class if no higher level interface could be matched against or the interface equivalent class.
69       */
70      Class<?> getInterfaceClass( Class<?> clazz );
71  
72      /**
73       * For the given {@link Method} and class finds the highest level interface class this combination can be cast to.
74       * 
75       * @param m The method the class must implement.
76       * @param clazz The current class being worked with.
77       * @return The highest level interface / class that the referenced {@link Method} is declared in.
78       */
79      Class<?> getSuperOrInterfaceClass( Method m, Class<?> clazz );
80  
81      /**
82       * For a given root object type returns the base class type to be used in root referenced expressions. This helps in
83       * some instances where the root objects themselves are compiled javassist instances that need more generic class
84       * equivalents to cast to.
85       * 
86       * @param rootNode The root expression node.
87       * @param context The current execution context.
88       * @return The root expression class type to cast to for this node.
89       */
90      Class<?> getRootExpressionClass( Node rootNode, OgnlContext context );
91  
92      /**
93       * Used primarily by AST types like {@link org.apache.commons.ognl.ASTChain} where <code>foo.bar.id</code> type
94       * references may need to be cast multiple times in order to properly resolve the members in a compiled statement.
95       * <p>
96       * This method should be using the various {@link org.apache.commons.ognl.OgnlContext#getCurrentType()} /
97       * {@link org.apache.commons.ognl.OgnlContext#getCurrentAccessor()} methods to inspect the type stack and properly
98       * cast to the right classes - but only when necessary.
99       * </p>
100      * 
101      * @param context The current execution context.
102      * @param expression The node being checked for casting.
103      * @param body The java source string generated by the given node.
104      * @return The body string parameter plus any additional casting syntax needed to make the expression resolvable.
105      */
106     String castExpression( OgnlContext context, Node expression, String body );
107 
108     /**
109      * Method is used for expressions where multiple inner parameter method calls in generated java source strings cause
110      * javassit failures. It is hacky and cumbersome to have to generate expressions this way but it's the only current
111      * known way to make javassist happy.
112      * <p>
113      * Takes an expression block generated by a node and creates a new method on the base object being compiled so that
114      * sufficiently complicated sub expression blocks can be broken out in to distinct methods to be referenced by the
115      * core accessor / setter methods in the base compiled root object.
116      * </p>
117      * 
118      * @param context The current execution context.
119      * @param expression The java source expression to dump in to a seperate method reference.
120      * @param type The return type that should be specified for the new method.
121      * @return The method name that will be used to reference the sub expression in place of the actual sub expression
122      *         itself.
123      */
124     String createLocalReference( OgnlContext context, String expression, Class<?> type );
125 }