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Groovy example source code file (Log4j.java)

This example Groovy source code file (Log4j.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

annotation, argumentlistexpression, attributeexpression, classexpression, classexpression, classnode, classnode, enabled, expression, log4jloggingstrategy, methodcallexpression, methodcallexpression, string, string, target

The Groovy Log4j.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,
 * 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 groovy.util.logging;

import org.codehaus.groovy.ast.ClassHelper;
import org.codehaus.groovy.ast.ClassNode;
import org.codehaus.groovy.ast.FieldNode;
import org.codehaus.groovy.ast.expr.*;
import org.codehaus.groovy.transform.GroovyASTTransformationClass;
import org.codehaus.groovy.transform.LogASTTransformation;
import org.objectweb.asm.Opcodes;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * This local transform adds a logging ability to your program using
 * Log4j logging. Every method call on a unbound variable named <i>log
 * will be mapped to a call to the logger. For this a <i>log field will be
 * inserted in the class. If the field already exists the usage of this transform
 * will cause a compilation error. The method name will be used to determine
 * what to call on the logger.
 * <pre>
 * log.name(exp)
 * </pre>is mapped to
 * <pre>
 * if (log.isNameEnabled() {
 *    log.name(exp)
 * }</pre>
 * Here name is a place holder for info, debug, warning, error, etc.
 * If the expression exp is a constant or only a variable access the method call will
 * not be transformed. But this will still cause a call on the injected logger.
 *
 * @author Hamlet D'Arcy
 * @author Tomek Bujok
 * @since 1.8.0
 */
@java.lang.annotation.Documented
@Retention(RetentionPolicy.SOURCE)
@Target({ElementType.TYPE})
@GroovyASTTransformationClass("org.codehaus.groovy.transform.LogASTTransformation")
public @interface Log4j {
    String value() default "log";
    Class<? extends LogASTTransformation.LoggingStrategy> loggingStrategy() default Log4jLoggingStrategy.class;

    public static class Log4jLoggingStrategy implements LogASTTransformation.LoggingStrategy {
        public FieldNode addLoggerFieldToClass(ClassNode classNode, String logFieldName) {
            return classNode.addField(logFieldName,
                    Opcodes.ACC_FINAL | Opcodes.ACC_TRANSIENT | Opcodes.ACC_STATIC | Opcodes.ACC_PRIVATE,
                    new ClassNode("org.apache.log4j.Logger", Opcodes.ACC_PUBLIC, ClassHelper.OBJECT_TYPE),
                    new MethodCallExpression(
                            new ClassExpression(new ClassNode("org.apache.log4j.Logger", Opcodes.ACC_PUBLIC, ClassHelper.OBJECT_TYPE)),
                            "getLogger",
                            new ClassExpression(classNode)));
        }

        public boolean isLoggingMethod(String methodName) {
            return methodName.matches("fatal|error|warn|info|debug|trace");
        }

        public Expression wrapLoggingMethodCall(Expression logVariable, String methodName, Expression originalExpression) {
            final MethodCallExpression condition;
            if (!"trace".equals(methodName)) {
                ClassNode levelClass = new ClassNode("org.apache.log4j.Priority", 0, ClassHelper.OBJECT_TYPE);
                AttributeExpression logLevelExpression = new AttributeExpression(
                        new ClassExpression(levelClass),
                        new ConstantExpression(methodName.toUpperCase()));
                ArgumentListExpression args = new ArgumentListExpression();
                args.addExpression(logLevelExpression);
                condition = new MethodCallExpression(logVariable, "isEnabledFor", args);
            } else {
                // log4j api is inconsistent, so trace requires special handling
                condition = new MethodCallExpression(
                        logVariable,
                        "is" + methodName.substring(0, 1).toUpperCase() + methodName.substring(1, methodName.length()) + "Enabled",
                        ArgumentListExpression.EMPTY_ARGUMENTS);
            }

            return new TernaryExpression(
                    new BooleanExpression(condition),
                    originalExpression,
                    ConstantExpression.NULL);
        }
    }
}

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