predicate.java

java1.6众多例子参考

                if (_nthPositionFilter) {
                    SyntaxTreeNode parent = getParent();
                    _nthDescendant = (parent instanceof Step) &&
                        (parent.getParent() instanceof AbsoluteLocationPath);
                    return _type = Type.NodeSet;
                }
            }          

           // Reset optimization flags
            _nthPositionFilter = _nthDescendant = false;
            
           // Otherwise, expand [e] to [position() = e]
           final QName position = 
                getParser().getQNameIgnoreDefaultNs("position");
           final PositionCall positionCall =
                new PositionCall(position);
           positionCall.setParser(getParser());
           positionCall.setParent(this);

           _exp = new EqualityExpr(Operators.EQ, positionCall,
                                    _exp);
           if (_exp.typeCheck(stable) != Type.Boolean) {
               _exp = new CastExpr(_exp, Type.Boolean);
           }
           return _type = Type.Boolean;
	}
	else {
            // All other types will be handled as boolean values
	    if (texp instanceof BooleanType == false) {
		_exp = new CastExpr(_exp, Type.Boolean);
            }
            return _type = Type.Boolean;
	}
    }
	
    /**
     * Create a new "Filter" class implementing
     * <code>CurrentNodeListFilter</code>. Allocate registers for local 
     * variables and local parameters passed in the closure to test().
     * Notice that local variables need to be "unboxed".
     */
    private void compileFilter(ClassGenerator classGen,
			       MethodGenerator methodGen) {
	TestGenerator testGen;
	LocalVariableGen local;
	FilterGenerator filterGen;

	_className = getXSLTC().getHelperClassName();
	filterGen = new FilterGenerator(_className,
					"java.lang.Object",
					toString(), 
					ACC_PUBLIC | ACC_SUPER,
					new String[] {
					    CURRENT_NODE_LIST_FILTER
					},
					classGen.getStylesheet());	

	final ConstantPoolGen cpg = filterGen.getConstantPool();
	final int length = (_closureVars == null) ? 0 : _closureVars.size();

	// Add a new instance variable for each var in closure
	for (int i = 0; i < length; i++) {
	    VariableBase var = ((VariableRefBase) _closureVars.get(i)).getVariable();

	    filterGen.addField(new Field(ACC_PUBLIC, 
					cpg.addUtf8(var.getEscapedName()),
					cpg.addUtf8(var.getType().toSignature()),
					null, cpg.getConstantPool()));
	}

	final InstructionList il = new InstructionList();
	testGen = new TestGenerator(ACC_PUBLIC | ACC_FINAL,
				    com.sun.org.apache.bcel.internal.generic.Type.BOOLEAN, 
				    new com.sun.org.apache.bcel.internal.generic.Type[] {
					com.sun.org.apache.bcel.internal.generic.Type.INT,
					com.sun.org.apache.bcel.internal.generic.Type.INT,
					com.sun.org.apache.bcel.internal.generic.Type.INT,
					com.sun.org.apache.bcel.internal.generic.Type.INT,
					Util.getJCRefType(TRANSLET_SIG),
					Util.getJCRefType(NODE_ITERATOR_SIG)
				    },
				    new String[] {
					"node",
					"position",
					"last",
					"current",
					"translet",
					"iterator"
				    },
				    "test", _className, il, cpg);
		
	// Store the dom in a local variable
	local = testGen.addLocalVariable("document",
					 Util.getJCRefType(DOM_INTF_SIG),
					 null, null);
	final String className = classGen.getClassName();
	il.append(filterGen.loadTranslet());
	il.append(new CHECKCAST(cpg.addClass(className)));
	il.append(new GETFIELD(cpg.addFieldref(className,
					       DOM_FIELD, DOM_INTF_SIG)));
	il.append(new ASTORE(local.getIndex()));

	// Store the dom index in the test generator
	testGen.setDomIndex(local.getIndex());

	_exp.translate(filterGen, testGen);
	il.append(IRETURN);
	
	testGen.stripAttributes(true);
	testGen.setMaxLocals();
	testGen.setMaxStack();
	testGen.removeNOPs();
	filterGen.addEmptyConstructor(ACC_PUBLIC);
	filterGen.addMethod(testGen.getMethod());
		
	getXSLTC().dumpClass(filterGen.getJavaClass());
    }

    /**
     * Returns true if the predicate is a test for the existance of an
     * element or attribute. All we have to do is to get the first node
     * from the step, check if it is there, and then return true/false.
     */
    public boolean isBooleanTest() {
	return (_exp instanceof BooleanExpr);
    }

    /**
     * Method to see if we can optimise the predicate by using a specialised
     * iterator for expressions like '/foo/bar[@attr = $var]', which are
     * very common in many stylesheets
     */
    public boolean isNodeValueTest() {
	if (!_canOptimize) return false;
	return (getStep() != null && getCompareValue() != null);
    }

   /**
     * Returns the step in an expression of the form 'step = value'. 
     * Null is returned if the expression is not of the right form.
     * Optimization if off if null is returned.
     */
    public Step getStep() {
        // Returned cached value if called more than once
	if (_step != null) {
            return _step;
        }
        
        // Nothing to do if _exp is null
	if (_exp == null) {
            return null;
        }

        // Ignore if not equality expression
	if (_exp instanceof EqualityExpr) {
	    EqualityExpr exp = (EqualityExpr)_exp;
	    Expression left = exp.getLeft();
	    Expression right = exp.getRight();

            // Unwrap and set _step if appropriate
	    if (left instanceof CastExpr) {
                left = ((CastExpr) left).getExpr();
            }
	    if (left instanceof Step) {
                _step = (Step) left;
            }
	    
            // Unwrap and set _step if appropriate
	    if (right instanceof CastExpr) {
                right = ((CastExpr)right).getExpr();
            }
	    if (right instanceof Step) {
                _step = (Step)right;
            }
	}
	return _step;
    }

    /**
     * Returns the value in an expression of the form 'step = value'. 
     * A value may be either a literal string or a variable whose 
     * type is string. Optimization if off if null is returned.
     */
    public Expression getCompareValue() {
        // Returned cached value if called more than once
	if (_value != null) {
            return _value;
        }
        
        // Nothing to to do if _exp is null
	if (_exp == null) {
            return null;
        }

        // Ignore if not an equality expression
	if (_exp instanceof EqualityExpr) {
	    EqualityExpr exp = (EqualityExpr) _exp;
	    Expression left = exp.getLeft();
	    Expression right = exp.getRight();
            
            // Return if left is literal string
            if (left instanceof LiteralExpr) {
                _value = left;
                return _value;
            }
            // Return if left is a variable reference of type string
            if (left instanceof VariableRefBase &&
                left.getType() == Type.String) 
            {
                _value = left;
                return _value;
            }
            
            // Return if right is literal string
            if (right instanceof LiteralExpr) {
                _value = right;
                return _value;
            }
            // Return if left is a variable reference whose type is string
            if (right instanceof VariableRefBase &&
                right.getType() == Type.String) 
            {
                _value = right;
                return _value;
            }
	}
	return null;
    }
 
    /**
     * Translate a predicate expression. This translation pushes
     * two references on the stack: a reference to a newly created
     * filter object and a reference to the predicate's closure.
     */
    public void translateFilter(ClassGenerator classGen,
				MethodGenerator methodGen) 
    {
	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();

	// Compile auxiliary class for filter
	compileFilter(classGen, methodGen);
	
	// Create new instance of filter
	il.append(new NEW(cpg.addClass(_className)));
	il.append(DUP);
	il.append(new INVOKESPECIAL(cpg.addMethodref(_className,
						     "<init>", "()V")));

	// Initialize closure variables
	final int length = (_closureVars == null) ? 0 : _closureVars.size();

	for (int i = 0; i < length; i++) {
	    VariableRefBase varRef = (VariableRefBase) _closureVars.get(i);
	    VariableBase var = varRef.getVariable();
	    Type varType = var.getType();

	    il.append(DUP);

	    // Find nearest closure implemented as an inner class
	    Closure variableClosure = _parentClosure;
	    while (variableClosure != null) {
		if (variableClosure.inInnerClass()) break;
		variableClosure = variableClosure.getParentClosure();
	    }

	    // Use getfield if in an inner class
	    if (variableClosure != null) {
		il.append(ALOAD_0);
		il.append(new GETFIELD(
		    cpg.addFieldref(variableClosure.getInnerClassName(), 
			var.getEscapedName(), varType.toSignature())));
	    }
	    else {
		// Use a load of instruction if in translet class
		il.append(var.loadInstruction());
	    }

	    // Store variable in new closure
	    il.append(new PUTFIELD(
		    cpg.addFieldref(_className, var.getEscapedName(), 
			varType.toSignature())));
	}
    }
    
    /**
     * Translate a predicate expression. If non of the optimizations apply
     * then this translation pushes two references on the stack: a reference 
     * to a newly created filter object and a reference to the predicate's 
     * closure. See class <code>Step</code> for further details.
     */
    public void translate(ClassGenerator classGen, MethodGenerator methodGen) {

	final ConstantPoolGen cpg = classGen.getConstantPool();
	final InstructionList il = methodGen.getInstructionList();

	if (_nthPositionFilter || _nthDescendant) {
	    _exp.translate(classGen, methodGen);
	}
	else if (isNodeValueTest() && (getParent() instanceof Step)) {
	    _value.translate(classGen, methodGen);
	    il.append(new CHECKCAST(cpg.addClass(STRING_CLASS)));
	    il.append(new PUSH(cpg, ((EqualityExpr)_exp).getOp()));
	}
	else {
	    translateFilter(classGen, methodGen);
	}
    }
}