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Groovy example source code file (LogASTTransformation.java)

This example Groovy source code file (LogASTTransformation.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

annotatednode, annotationnode, class, class, classnode, expression, expression, loggingstrategy, loggingstrategy, reflection, runtimeexception, sourceunit, string, string, util, variableexpression

The Groovy LogASTTransformation.java source code

 * Copyright 2003-2010 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,
 * See the License for the specific language governing permissions and
 * limitations under the License.
package org.codehaus.groovy.transform;

import org.codehaus.groovy.GroovyBugError;
import org.codehaus.groovy.ast.*;
import org.codehaus.groovy.ast.expr.*;
import org.codehaus.groovy.control.CompilePhase;
import org.codehaus.groovy.control.SourceUnit;
import org.codehaus.groovy.control.messages.SyntaxErrorMessage;
import org.codehaus.groovy.syntax.SyntaxException;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Arrays;

 * This class provides an AST Transformation to add a log field to a class.
 * @author Guillaume Laforge
 * @author Jochen Theodorou
 * @author Dinko Srkoc
 * @author Hamlet D'Arcy
 * @author Raffaele Cigni
 * @author Alberto Vilches Raton
 * @author Tomasz Bujok
 * @author Martin Ghados
 * @author Matthias Cullmann
@GroovyASTTransformation(phase = CompilePhase.SEMANTIC_ANALYSIS)
public class LogASTTransformation implements ASTTransformation {

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

        AnnotatedNode targetClass = (AnnotatedNode) nodes[1];
        AnnotationNode logAnnotation = (AnnotationNode) nodes[0];

        final LoggingStrategy loggingStrategy = createLoggingStrategy(logAnnotation);
        if (loggingStrategy == null) return;

        final String logFieldName = lookupLogFieldName(logAnnotation);

        if (!(targetClass instanceof ClassNode))
            throw new GroovyBugError("Class annotation " + logAnnotation.getClassNode().getName() + " annotated no Class, this must not happen.");

        final ClassNode classNode = (ClassNode) targetClass;

        ClassCodeExpressionTransformer transformer = new ClassCodeExpressionTransformer() {
            private FieldNode logNode;

            protected SourceUnit getSourceUnit() {
                return source;

            public Expression transform(Expression exp) {
                if (exp == null) return null;
                if (exp instanceof MethodCallExpression) {
                    return transformMethodCallExpression(exp);
                return super.transform(exp);

            public void visitClass(ClassNode node) {
                FieldNode logField = node.getField(logFieldName);
                if (logField != null && logField.getOwner().equals(node)) {
                    addError("Class annotated with Log annotation cannot have log field declared", logField);
                } else if (logField != null && !Modifier.isPrivate(logField.getModifiers())) {
                    addError("Class annotated with Log annotation cannot have log field declared because the field exists in the parent class: " + logField.getOwner().getName(), logField);
                } else {
                    logNode = loggingStrategy.addLoggerFieldToClass(node, logFieldName);

            private Expression transformMethodCallExpression(Expression exp) {
                MethodCallExpression mce = (MethodCallExpression) exp;
                if (!(mce.getObjectExpression() instanceof VariableExpression)) {
                    return exp;
                VariableExpression variableExpression = (VariableExpression) mce.getObjectExpression();
                if (!variableExpression.getName().equals(logFieldName)
                        || !(variableExpression.getAccessedVariable() instanceof DynamicVariable)) {
                    return exp;
                String methodName = mce.getMethodAsString();
                if (methodName == null) return exp;
                if (usesSimpleMethodArgumentsOnly(mce)) return exp;


                if (!loggingStrategy.isLoggingMethod(methodName)) return exp;

                return loggingStrategy.wrapLoggingMethodCall(variableExpression, methodName, exp);

            private boolean usesSimpleMethodArgumentsOnly(MethodCallExpression mce) {
                Expression arguments = mce.getArguments();
                if (arguments instanceof TupleExpression) {
                    TupleExpression tuple = (TupleExpression) arguments;
                    for (Expression exp : tuple.getExpressions()) {
                        if (!isSimpleExpression(exp)) return false;
                    return true;
                return !isSimpleExpression(arguments);

            private boolean isSimpleExpression(Expression exp) {
                if (exp instanceof ConstantExpression) return true;
                if (exp instanceof VariableExpression) return true;
                return false;



    private String lookupLogFieldName(AnnotationNode logAnnotation) {
        Expression member = logAnnotation.getMember("value");
        if (member != null && member.getText() != null) {
            return member.getText();
        } else {
            return "log";

    public void addError(String msg, ASTNode expr, SourceUnit source) {
        int line = expr.getLineNumber();
        int col = expr.getColumnNumber();
                new SyntaxErrorMessage(new SyntaxException(msg + '\n', line, col), source)

    private LoggingStrategy createLoggingStrategy(AnnotationNode logAnnotation) {

        String annotationName = logAnnotation.getClassNode().getName();

        Class annotationClass;
        try {
            annotationClass = Class.forName(annotationName);
        } catch (Throwable e) {
            throw new RuntimeException("Could not resolve class named " + annotationName);

        Method annotationMethod;
        try {
            annotationMethod = annotationClass.getDeclaredMethod("loggingStrategy", (Class[]) null);
        } catch (Throwable e) {
            throw new RuntimeException("Could not find method named loggingStrategy on class named " + annotationName);

        Object defaultValue;
        try {
            defaultValue = annotationMethod.getDefaultValue();
        } catch (Throwable e) {
            throw new RuntimeException("Could not find default value of method named loggingStrategy on class named " + annotationName);

        if (!LoggingStrategy.class.isAssignableFrom((Class) defaultValue)) {
            throw new RuntimeException("Default loggingStrategy value on class named " + annotationName + " is not a LoggingStrategy");

        try {
            Class<? extends LoggingStrategy> strategyClass = (Class) defaultValue;
            return strategyClass.newInstance();
        } catch (Exception e) {
            return null;

     * A LoggingStrategy defines how to wire a new logger instance into an existing class.
     * It is meant to be used with the @Log family of annotations to allow you to
     * write your own Log annotation provider.
    public interface LoggingStrategy {
         * In this method, you are given a ClassNode and a field name, and you must add a new Field
         * onto the class. Return the result of the ClassNode.addField operations.
         * @param classNode the class that was originally annotated with the Log transformation.
         * @param fieldName the name of the logger field
         * @return the FieldNode instance that was created and added to the class
        FieldNode addLoggerFieldToClass(ClassNode classNode, String fieldName);

        boolean isLoggingMethod(String methodName);

        Expression wrapLoggingMethodCall(Expression logVariable, String methodName, Expression originalExpression);

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