Tomcat example source code file (Catch.java)

This example Tomcat source code file (Catch.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

catch, catch, string, string, tagplugin, tagplugin

The Tomcat Catch.java source code

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


package org.apache.jasper.tagplugins.jstl.core;

import org.apache.jasper.compiler.tagplugin.TagPlugin;
import org.apache.jasper.compiler.tagplugin.TagPluginContext;

public class Catch implements TagPlugin {
    
    public void doTag(TagPluginContext ctxt) {
        
        //flag for the existence of the var attribute
        boolean hasVar = ctxt.isAttributeSpecified("var");
        
        //temp name for exception and caught
        String exceptionName = ctxt.getTemporaryVariableName();
        String caughtName = ctxt.getTemporaryVariableName();
        
        //main part to generate code
        ctxt.generateJavaSource("boolean " + caughtName + " = false;");
        ctxt.generateJavaSource("try{");
        ctxt.generateBody();
        ctxt.generateJavaSource("}");
        
        //do catch
        ctxt.generateJavaSource("catch(Throwable " + exceptionName + "){");
        
        //if the var specified, the exception object should 
        //be set to the attribute "var" defines in page scope 
        if(hasVar){
            String strVar = ctxt.getConstantAttribute("var");
            ctxt.generateJavaSource("    pageContext.setAttribute(\"" + strVar + "\", " 
                    + exceptionName + ", PageContext.PAGE_SCOPE);");
        }
        
        //whenever there's exception caught, 
        //the flag caught should be set true;
        ctxt.generateJavaSource("    " + caughtName + " = true;");
        ctxt.generateJavaSource("}");
        
        //do finally
        ctxt.generateJavaSource("finally{");
        
        //if var specified, the attribute it defines 
        //in page scope should be removed
        if(hasVar){
            String strVar = ctxt.getConstantAttribute("var");
            ctxt.generateJavaSource("    if(!" + caughtName + "){");
            ctxt.generateJavaSource("        pageContext.removeAttribute(\"" + strVar + "\", PageContext.PAGE_SCOPE);");
            ctxt.generateJavaSource("    }");
        }
        
        ctxt.generateJavaSource("}");
    }
    
}