com.nginious.http.xsp.expr.LengthFunction.java Source code

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Here is the source code for com.nginious.http.xsp.expr.LengthFunction.java

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/**
 * Copyright 2012 NetDigital Sweden AB
 *
 * 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.
*/

package com.nginious.http.xsp.expr;

import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

/**
 * A function which takes on value argument and returns the length of a string when evaluated. 
 * Below is an example which evaluates to 4.
 * 
 * <pre>
 * length('Test')
 * </pre>
 * 
 * @author Bojan Pisler, NetDigital Sweden AB
 *
 */
public class LengthFunction extends Function {

    private Value value;

    /**
     * Constructs a new length function with the specified value as argument.
     * 
     * @param value
     */
    public LengthFunction(Value value) {
        super();
        this.value = value;
    }

    /**
     * Returns the type of value returned by this function when evaluated, {@link Type#INT}.
     * 
     * @return the type 
     */
    protected Type getType() {
        return Type.INT;
    }

    /**
     * Evaluates this function which returns the length of a string.
     * 
     * @return the result of evaluating this function
     */
    protected Value evaluate() {
        return new IntegerValue(getIntValue());
    }

    /**
     * Evaluates this function and returns the length as an integer.
     * 
     * @return the integer result of evaluating this function 
     */
    protected int getIntValue() {
        String expr = value.getStringValue();

        if (expr == null) {
            return 0;
        }

        return expr.length();
    }

    /**
     * Evaluates this function and returns the length converted to a double.
     * 
     * @return the double result of evaluating this function
     */
    protected double getDoubleValue() {
        return (double) getIntValue();
    }

    /**
     * Evaluates this function and returns the length converted to a string.
     * 
     * @return the string result of evaluating this function
     */
    protected String getStringValue() {
        return Integer.toString(getIntValue());
    }

    /**
     * Evaluates this function and returns the length converted to a boolean.
     * 
     * @return the boolean result of evaluating this function
     */
    protected boolean getBooleanValue() {
        return getIntValue() != 0;
    }

    /**
     * Creates bytecode for evaluating this function. The specified method
     * visitor is used to generate bytecode. The generated bytecode produces
     * a result of the specified type.
     * 
     * @param visitor the method visitor
     * @param type the type
     */
    void compile(MethodVisitor visitor, Type type) {
        value.compile(visitor, Type.STRING);
        visitor.visitVarInsn(Opcodes.ASTORE, 1);

        Label nullLabel = new Label();
        Label notNullLabel = new Label();

        visitor.visitVarInsn(Opcodes.ALOAD, 1);
        visitor.visitJumpInsn(Opcodes.IFNULL, nullLabel);

        visitor.visitVarInsn(Opcodes.ALOAD, 1);
        visitor.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/lang/String", "length", "()I");
        visitor.visitJumpInsn(Opcodes.GOTO, notNullLabel);

        visitor.visitLabel(nullLabel);
        visitor.visitLdcInsn(0);

        visitor.visitLabel(notNullLabel);
    }
}