foreach.java

java1.6众多例子参考

/*
 * Copyright 2001-2004 The Apache Software Foundation.
 *
 * Licensed 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.
 */
/*
 * $Id: ForEach.java,v 1.2.4.1 2005/09/01 15:23:46 pvedula Exp $
 */

package com.sun.org.apache.xalan.internal.xsltc.compiler;

import java.util.Enumeration;
import java.util.Vector;

import com.sun.org.apache.bcel.internal.generic.BranchHandle;
import com.sun.org.apache.bcel.internal.generic.ConstantPoolGen;
import com.sun.org.apache.bcel.internal.generic.GOTO;
import com.sun.org.apache.bcel.internal.generic.IFGT;
import com.sun.org.apache.bcel.internal.generic.InstructionHandle;
import com.sun.org.apache.bcel.internal.generic.InstructionList;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ClassGenerator;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ErrorMsg;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.MethodGenerator;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.NodeSetType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.NodeType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ReferenceType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.ResultTreeType;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.Type;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.TypeCheckError;
import com.sun.org.apache.xalan.internal.xsltc.compiler.util.Util;

/**
 * @author Jacek Ambroziak
 * @author Santiago Pericas-Geertsen
 * @author Morten Jorgensen
 */
final class ForEach extends Instruction {

    private Expression _select;
    private Type       _type;

    public void display(int indent) {
	indent(indent);
	Util.println("ForEach");
	indent(indent + IndentIncrement);
	Util.println("select " + _select.toString());
	displayContents(indent + IndentIncrement);
    }
		
    public void parseContents(Parser parser) {
	_select = parser.parseExpression(this, "select", null);

	parseChildren(parser);

        // make sure required attribute(s) have been set
        if (_select.isDummy()) {
	    reportError(this, parser, ErrorMsg.REQUIRED_ATTR_ERR, "select");
        }
    }
	
    public Type typeCheck(SymbolTable stable) throws TypeCheckError {
	_type = _select.typeCheck(stable);

	if (_type instanceof ReferenceType || _type instanceof NodeType) {
	    _select = new CastExpr(_select, Type.NodeSet);
	    typeCheckContents(stable);
	    return Type.Void;
	}
	if (_type instanceof NodeSetType||_type instanceof ResultTreeType) {
	    typeCheckContents(stable);
	    return Type.Void;
	}
	throw new TypeCheckError(this);
    }

    public void translate(ClassGenerator classGen, MethodGenerator methodGen) {
	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();

	// Save current node and current iterator on the stack
	il.append(methodGen.loadCurrentNode());
	il.append(methodGen.loadIterator());
		
	// Collect sort objects associated with this instruction
	final Vector sortObjects = new Vector();
	Enumeration children = elements();
	while (children.hasMoreElements()) {
	    final Object child = children.nextElement();
	    if (child instanceof Sort) {
		sortObjects.addElement(child);
	    }
	}

	if ((_type != null) && (_type instanceof ResultTreeType)) {
	    // Store existing DOM on stack - must be restored when loop is done
	    il.append(methodGen.loadDOM());

	    // <xsl:sort> cannot be applied to a result tree - issue warning
	    if (sortObjects.size() > 0) {
		ErrorMsg msg = new ErrorMsg(ErrorMsg.RESULT_TREE_SORT_ERR,this);
		getParser().reportError(WARNING, msg);
	    }

	    // Put the result tree on the stack (DOM)
	    _select.translate(classGen, methodGen);
	    // Get an iterator for the whole DOM - excluding the root node
	    _type.translateTo(classGen, methodGen, Type.NodeSet);
	    // Store the result tree as the default DOM
	    il.append(SWAP);
	    il.append(methodGen.storeDOM());
	}
	else {
	    // Compile node iterator
	    if (sortObjects.size() > 0) {
		Sort.translateSortIterator(classGen, methodGen,
					   _select, sortObjects);
	    }
	    else {
		_select.translate(classGen, methodGen);
	    }

	    if (_type instanceof ReferenceType == false) {
                il.append(methodGen.loadContextNode());
                il.append(methodGen.setStartNode());
	    }
	}


	// Overwrite current iterator
	il.append(methodGen.storeIterator());

	// Give local variables (if any) default values before starting loop
	initializeVariables(classGen, methodGen);

	final BranchHandle nextNode = il.append(new GOTO(null));
	final InstructionHandle loop = il.append(NOP);

	translateContents(classGen, methodGen);
		    
	nextNode.setTarget(il.append(methodGen.loadIterator()));
	il.append(methodGen.nextNode());
	il.append(DUP);
	il.append(methodGen.storeCurrentNode());
	il.append(new IFGT(loop));

	// Restore current DOM (if result tree was used instead for this loop)
	if ((_type != null) && (_type instanceof ResultTreeType)) {
	    il.append(methodGen.storeDOM());	    
	}

	// Restore current node and current iterator from the stack
	il.append(methodGen.storeIterator());
	il.append(methodGen.storeCurrentNode());
    }

    /**
     * The code that is generated by nested for-each loops can appear to some
     * JVMs as if it is accessing un-initialized variables. We must add some
     * code that pushes the default variable value on the stack and pops it
     * into the variable slot. This is done by the Variable.initialize()
     * method. The code that we compile for this loop looks like this:
     *
     *           initialize iterator
     *           initialize variables <-- HERE!!!
     *           goto   Iterate
     *  Loop:    :
     *           : (code for <xsl:for-each> contents)
     *           :
     *  Iterate: node = iterator.next();
     *           if (node != END) goto Loop
     */
    public void initializeVariables(ClassGenerator classGen,
				   MethodGenerator methodGen) {
	final int n = elementCount();
	for (int i = 0; i < n; i++) {
	    final Object child = getContents().elementAt(i);
	    if (child instanceof Variable) {
		Variable var = (Variable)child;
		var.initialize(classGen, methodGen);
	    }
	}
    }

}