Groovy example source code file (LazyASTTransformation.java)

This example Groovy source code file (LazyASTTransformation.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 - Groovy tags/keywords

assign, assign, binaryexpression, binaryexpression, blockstatement, classnode, compare_not_equal, expression, expression, expressionstatement, expressionstatement, fieldnode, null_expr, util, variableexpression

The Groovy LazyASTTransformation.java source code

/*
 * Copyright 2008-2010 the original author or authors.
 *
 * 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 org.codehaus.groovy.transform;

import org.codehaus.groovy.ast.*;
import org.codehaus.groovy.ast.expr.*;
import org.codehaus.groovy.ast.stmt.*;
import org.codehaus.groovy.control.CompilePhase;
import org.codehaus.groovy.control.SourceUnit;
import org.codehaus.groovy.runtime.MetaClassHelper;
import org.codehaus.groovy.syntax.Token;
import org.objectweb.asm.Opcodes;

import java.lang.ref.SoftReference;
import java.util.Arrays;

/**
 * Handles generation of code for the @Lazy annotation
 *
 * @author Alex Tkachman
 * @author Paul King
 */
@GroovyASTTransformation(phase = CompilePhase.CANONICALIZATION)
public class LazyASTTransformation implements ASTTransformation, Opcodes {

    private static final ClassNode SOFT_REF = ClassHelper.makeWithoutCaching(SoftReference.class, false);
    private static final Expression NULL_EXPR = ConstantExpression.NULL;
    private static final Token ASSIGN = Token.newSymbol("=", -1, -1);
    private static final Token COMPARE_NOT_EQUAL = Token.newSymbol("!=", -1, -1);

    public void visit(ASTNode[] nodes, SourceUnit source) {
        if (nodes.length != 2 || !(nodes[0] instanceof AnnotationNode) || !(nodes[1] instanceof AnnotatedNode)) {
            throw new RuntimeException("Internal error: expecting [AnnotationNode, AnnotatedNode] but got: " + Arrays.asList(nodes));
        }

        AnnotatedNode parent = (AnnotatedNode) nodes[1];
        AnnotationNode node = (AnnotationNode) nodes[0];

        if (parent instanceof FieldNode) {
            final FieldNode fieldNode = (FieldNode) parent;
            final Expression member = node.getMember("soft");
            final Expression init = getInitExpr(fieldNode);

            fieldNode.rename("$" + fieldNode.getName());
            fieldNode.setModifiers(ACC_PRIVATE | (fieldNode.getModifiers() & (~(ACC_PUBLIC | ACC_PROTECTED))));
            
            if (member instanceof ConstantExpression && ((ConstantExpression) member).getValue().equals(true))
                createSoft(fieldNode, init);
            else {
                create(fieldNode, init);
                // @Lazy not meaningful with primitive so convert to wrapper if needed
                if (ClassHelper.isPrimitiveType(fieldNode.getType())) {
                    fieldNode.setType(ClassHelper.getWrapper(fieldNode.getType()));
                }
            }
        }
    }

    private void create(FieldNode fieldNode, final Expression initExpr) {
        final BlockStatement body = new BlockStatement();
        if (fieldNode.isStatic()) {
            addHolderClassIdiomBody(body, fieldNode, initExpr);
        } else if (isVolatile(fieldNode)) {
            addNonThreadSafeBody(body, fieldNode, initExpr);
        } else {
            addDoubleCheckedLockingBody(body, fieldNode, initExpr);
        }
        addMethod(fieldNode, body, fieldNode.getType());
    }

    private void addHolderClassIdiomBody(BlockStatement body, FieldNode fieldNode, Expression initExpr) {
        final ClassNode declaringClass = fieldNode.getDeclaringClass();
        final ClassNode fieldType = fieldNode.getType();
        final int visibility = ACC_PRIVATE | ACC_STATIC;
        final String fullName = declaringClass.getName() + "$" + fieldType.getNameWithoutPackage() + "Holder_" + fieldNode.getName().substring(1);
        final InnerClassNode holderClass = new InnerClassNode(declaringClass, fullName, visibility, ClassHelper.OBJECT_TYPE);
        final String innerFieldName = "INSTANCE";
        holderClass.addField(innerFieldName, ACC_PRIVATE | ACC_STATIC | ACC_FINAL, fieldType, initExpr);
        final Expression innerField = new PropertyExpression(new ClassExpression(holderClass), innerFieldName);
        declaringClass.getModule().addClass(holderClass);
        body.addStatement(new ReturnStatement(innerField));
    }

    private void addDoubleCheckedLockingBody(BlockStatement body, FieldNode fieldNode, Expression initExpr) {
        final Expression fieldExpr = new VariableExpression(fieldNode);
        final VariableExpression localVar = new VariableExpression(fieldNode.getName() + "_local");
        body.addStatement(new ExpressionStatement(new DeclarationExpression(localVar, ASSIGN, fieldExpr)));
        body.addStatement(new IfStatement(
                new BooleanExpression(new BinaryExpression(localVar, COMPARE_NOT_EQUAL, NULL_EXPR)),
                new ReturnStatement(localVar),
                new SynchronizedStatement(
                        synchTarget(fieldNode),
                        new IfStatement(
                                new BooleanExpression(new BinaryExpression(fieldExpr, COMPARE_NOT_EQUAL, NULL_EXPR)),
                                new ReturnStatement(fieldExpr),
                                new ReturnStatement(new BinaryExpression(fieldExpr, ASSIGN, initExpr))
                        )
                )
        ));
    }

    private void addNonThreadSafeBody(BlockStatement body, FieldNode fieldNode, Expression initExpr) {
        final Expression fieldExpr = new VariableExpression(fieldNode);
        body.addStatement(new IfStatement(
                new BooleanExpression(new BinaryExpression(fieldExpr, COMPARE_NOT_EQUAL, NULL_EXPR)),
                new ExpressionStatement(fieldExpr),
                new ExpressionStatement(new BinaryExpression(fieldExpr, ASSIGN, initExpr))
        ));
    }

    private void addMethod(FieldNode fieldNode, BlockStatement body, ClassNode type) {
        int visibility = ACC_PUBLIC;
        if (fieldNode.isStatic()) visibility |= ACC_STATIC;
        final String name = "get" + MetaClassHelper.capitalize(fieldNode.getName().substring(1));
        fieldNode.getDeclaringClass().addMethod(name, visibility, type, Parameter.EMPTY_ARRAY, ClassNode.EMPTY_ARRAY, body);
    }

    private void createSoft(FieldNode fieldNode, Expression initExpr) {
        final ClassNode type = fieldNode.getType();
        fieldNode.setType(SOFT_REF);
        createSoftGetter(fieldNode, initExpr, type);
        createSoftSetter(fieldNode, type);
    }

    private void createSoftGetter(FieldNode fieldNode, Expression initExpr, ClassNode type) {
        final BlockStatement body = new BlockStatement();
        final Expression fieldExpr = new VariableExpression(fieldNode);
        final Expression resExpr = new VariableExpression("res", type);
        final MethodCallExpression callExpression = new MethodCallExpression(fieldExpr, "get", new ArgumentListExpression());
        callExpression.setSafe(true);
        body.addStatement(new ExpressionStatement(new DeclarationExpression(resExpr, ASSIGN, callExpression)));

        final BlockStatement elseBlock = new BlockStatement();
        elseBlock.addStatement(new ExpressionStatement(new BinaryExpression(resExpr, ASSIGN, initExpr)));
        elseBlock.addStatement(new ExpressionStatement(new BinaryExpression(fieldExpr, ASSIGN, new ConstructorCallExpression(SOFT_REF, resExpr))));
        elseBlock.addStatement(new ExpressionStatement(resExpr));

        final Statement mainIf = new IfStatement(
                new BooleanExpression(new BinaryExpression(resExpr, COMPARE_NOT_EQUAL, NULL_EXPR)),
                new ExpressionStatement(resExpr),
                elseBlock
        );

        if (isVolatile(fieldNode)) {
            body.addStatement(mainIf);
        } else {
            body.addStatement(new IfStatement(
                    new BooleanExpression(new BinaryExpression(resExpr, COMPARE_NOT_EQUAL, NULL_EXPR)),
                    new ExpressionStatement(resExpr),
                    new SynchronizedStatement(synchTarget(fieldNode), mainIf)
            ));
        }
        addMethod(fieldNode, body, type);
    }

    private void createSoftSetter(FieldNode fieldNode, ClassNode type) {
        final BlockStatement body = new BlockStatement();
        final Expression fieldExpr = new VariableExpression(fieldNode);
        final String name = "set" + MetaClassHelper.capitalize(fieldNode.getName().substring(1));
        final Parameter parameter = new Parameter(type, "value");
        final Expression paramExpr = new VariableExpression(parameter);
        body.addStatement(new IfStatement(
                new BooleanExpression(new BinaryExpression(paramExpr, COMPARE_NOT_EQUAL, NULL_EXPR)),
                new ExpressionStatement(new BinaryExpression(fieldExpr, ASSIGN, new ConstructorCallExpression(SOFT_REF, paramExpr))),
                new ExpressionStatement(new BinaryExpression(fieldExpr, ASSIGN, NULL_EXPR))
        ));
        int visibility = ACC_PUBLIC;
        if (fieldNode.isStatic()) visibility |= ACC_STATIC;
        fieldNode.getDeclaringClass().addMethod(name, visibility, ClassHelper.VOID_TYPE, new Parameter[]{parameter}, ClassNode.EMPTY_ARRAY, body);
    }

    private Expression synchTarget(FieldNode fieldNode) {
        return fieldNode.isStatic() ? new ClassExpression(fieldNode.getDeclaringClass()) : VariableExpression.THIS_EXPRESSION;
    }

    private boolean isVolatile(FieldNode fieldNode) {
        return (fieldNode.getModifiers() & ACC_VOLATILE) == 0;
    }

    private Expression getInitExpr(FieldNode fieldNode) {
        Expression initExpr = fieldNode.getInitialValueExpression();
        fieldNode.setInitialValueExpression(null);

        if (initExpr == null)
            initExpr = new ConstructorCallExpression(fieldNode.getType(), new ArgumentListExpression());

        return initExpr;
    }
}