openjpa-kernel-5/src/main/java/org/apache/openjpa/enhance/PCEnhancerAgent.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.apache.openjpa.enhance;

import java.lang.instrument.Instrumentation;

import org.apache.openjpa.conf.OpenJPAConfiguration;
import org.apache.openjpa.conf.OpenJPAConfigurationImpl;
import org.apache.openjpa.lib.conf.Configurations;
import org.apache.openjpa.lib.util.Options;
import org.apache.openjpa.lib.util.TemporaryClassLoader;
import org.apache.openjpa.util.ClassResolver;

/**
 * Java agent that makes persistent classes implement the
 * {@link PersistenceCapable} interface at runtime. The agent is launched
 * at JVM startup from the command line:
 * 
 * <code>java -javaagent:openjpa.jar[=&lt;options&gt;]</code>
 *  The options string should be formatted as a OpenJPA plugin, and may
 * contain any properties understood by the OpenJPA enhancer or any
 * configuration properties. For example:
 * 
 * <code>java -javaagent:openjpa.jar</code>
 *
 * @author Abe White
 */
public class PCEnhancerAgent {

    public static void premain(String args, Instrumentation inst) {
        OpenJPAConfiguration conf = new OpenJPAConfigurationImpl();
        Options opts = Configurations.parseProperties(args);
        Configurations.populateConfiguration(conf, opts);
        // don't allow connections
        conf.setConnectionUserName(null);
        conf.setConnectionPassword(null);
        conf.setConnectionURL(null);
        conf.setConnectionDriverName(null);
        conf.setConnectionFactoryName(null);
        // set single class resolver
        final ClassLoader tmpLoader = new TemporaryClassLoader(Thread.
            currentThread().getContextClassLoader());
        conf.setClassResolver(new ClassResolver() {
            public ClassLoader getClassLoader(Class context, ClassLoader env) {
                return tmpLoader;
            }
        });
        conf.setReadOnly(true);
        conf.instantiateAll(); // avoid threading issues

        PCClassFileTransformer transformer = new PCClassFileTransformer
            (conf.newMetaDataRepositoryInstance(), opts, tmpLoader);
        inst.addTransformer(transformer);
    }
}