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Java > Open Source Codes > bsh > BSHTryStatement


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3  * This file is part of the BeanShell Java Scripting distribution. *
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12  * The Original Code is BeanShell. The Initial Developer of the Original *
13  * Code is Pat Niemeyer. Portions created by Pat Niemeyer are Copyright *
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28  * Patrick Niemeyer (pat@pat.net) *
29  * Author of Learning Java, O'Reilly & Associates *
30  * http://www.pat.net/~pat/ *
31  * *
32  *****************************************************************************/
33
34
35 package bsh;
36
37 import java.util.Vector JavaDoc;
38
39 class BSHTryStatement extends SimpleNode
40 {
41     BSHTryStatement(int id)
42     {
43         super(id);
44     }
45
46     public Object JavaDoc eval( CallStack callstack, Interpreter interpreter)
47         throws EvalError
48     {
49         BSHBlock tryBlock = ((BSHBlock)jjtGetChild(0));
50
51         Vector JavaDoc catchParams = new Vector JavaDoc();
52         Vector JavaDoc catchBlocks = new Vector JavaDoc();
53
54         int nchild = jjtGetNumChildren();
55         Node node = null;
56         int i=1;
57         while((i < nchild) && ((node = jjtGetChild(i++)) instanceof BSHFormalParameter))
58         {
59             catchParams.addElement(node);
60             catchBlocks.addElement(jjtGetChild(i++));
61             node = null;
62         }
63         // finaly block
64 BSHBlock finallyBlock = null;
65         if(node != null)
66             finallyBlock = (BSHBlock)node;
67
68 // Why both of these?
69
70         TargetError target = null;
71         Throwable JavaDoc thrown = null;
72         Object JavaDoc ret = null;
73
74         /*
75             Evaluate the contents of the try { } block and catch any resulting
76             TargetErrors generated by the script.
77             We save the callstack depth and if an exception is thrown we pop
78             back to that depth before contiuing. The exception short circuited
79             any intervening method context pops.
80
81             Note: we the stack info... what do we do with it? append
82             to exception message?
83         */
84         int callstackDepth = callstack.depth();
85         try {
86             ret = tryBlock.eval(callstack, interpreter);
87         }
88         catch( TargetError e ) {
89             target = e;
90             String JavaDoc stackInfo = "Bsh Stack: ";
91             while ( callstack.depth() > callstackDepth )
92                 stackInfo += "\t" + callstack.pop() +"\n";
93         }
94
95         // unwrap the target error
96 if ( target != null )
97             thrown = target.getTarget();
98
99         
100         // If we have an exception, find a catch
101 if (thrown != null)
102         {
103             int n = catchParams.size();
104             for(i=0; i<n; i++)
105             {
106                 // Get catch block
107 BSHFormalParameter fp =
108                     (BSHFormalParameter)catchParams.elementAt(i);
109
110                 // Should cache this subject to classloader change message
111 // Evaluation of the formal parameter simply resolves its
112 // type via the specified namespace.. it doesn't modify the
113 // namespace.
114 fp.eval( callstack, interpreter );
115
116                 if ( fp.type == null && interpreter.getStrictJava() )
117                     throw new EvalError(
118                         "(Strict Java) Untyped catch block", this, callstack );
119
120                 // If the param is typed check assignability
121 if ( fp.type != null )
122                     try {
123                         thrown = (Throwable JavaDoc)Types.castObject(
124                             thrown/*rsh*/, fp.type/*lhsType*/, Types.ASSIGNMENT );
125                     } catch( UtilEvalError e ) {
126                         /*
127                             Catch the mismatch and continue to try the next
128                             Note: this is innefficient, should have an
129                             isAssignableFrom() that doesn't throw
130                             // TODO: we do now have a way to test assignment
131                             // in castObject(), use it?
132                         */
133                         continue;
134                     }
135
136                 // Found match, execute catch block
137 BSHBlock cb = (BSHBlock)(catchBlocks.elementAt(i));
138
139                 // Prepare to execute the block.
140 // We must create a new BlockNameSpace to hold the catch
141 // parameter and swap it on the stack after initializing it.
142
143                 NameSpace enclosingNameSpace = callstack.top();
144                 BlockNameSpace cbNameSpace =
145                     new BlockNameSpace( enclosingNameSpace );
146
147                 try {
148                     if ( fp.type == BSHFormalParameter.UNTYPED )
149                         // set an untyped variable directly in the block
150 cbNameSpace.setBlockVariable( fp.name, thrown );
151                     else
152                     {
153                         // set a typed variable (directly in the block)
154 Modifiers modifiers = new Modifiers();
155                         cbNameSpace.setTypedVariable(
156                             fp.name, fp.type, thrown, new Modifiers()/*none*/ );
157                     }
158                 } catch ( UtilEvalError e ) {
159                     throw new InterpreterError(
160                         "Unable to set var in catch block namespace." );
161                 }
162
163                 // put cbNameSpace on the top of the stack
164 callstack.swap( cbNameSpace );
165                 try {
166                     ret = cb.eval( callstack, interpreter );
167                 } finally {
168                     // put it back
169 callstack.swap( enclosingNameSpace );
170                 }
171
172                 target = null; // handled target
173 break;
174             }
175         }
176
177         // evaluate finally block
178 if(finallyBlock != null)
179             ret = finallyBlock.eval(callstack, interpreter);
180
181         // exception fell through, throw it upward...
182 if(target != null)
183             throw target;
184
185         if(ret instanceof ReturnControl)
186             return ret;
187         else
188             return Primitive.VOID;
189     }
190 }
191
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