/*
* Copyright (C) 2013 Brett Wooldridge
*
* 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.zaxxer.hikari.metrics;
import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtConstructor;
import javassist.LoaderClassPath;
import javassist.Modifier;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* This class is used to validate that Codahale metrics is available in the class
* path, or if not to generate a fake "shim" that avoids ClassNotFound exceptions
* in code that depends on (but does not use if not present) Codahale metrics.
*
* @author Brett Wooldridge
*/
public class CodaHaleShim
{
private static final Logger LOGGER = LoggerFactory.getLogger(CodaHaleShim.class);
private CodaHaleShim()
{
// empty
}
/**
* Simply invoking this method causes the initialization of this class. All work
* by this class is performed in static initialization.
*/
public static void initialize()
{
CodaHaleShim codaHaleShim = new CodaHaleShim();
codaHaleShim.loadOrShimCodahale();
}
/**
*
*/
private void loadOrShimCodahale()
{
ClassLoader contextClassLoader = Thread.currentThread().getContextClassLoader();
try {
CodaHaleShim.class.getClassLoader().loadClass("com.codahale.metrics.MetricRegistry");
}
catch (ClassNotFoundException e) {
// OK, it is not present, we have to generate a shim
LOGGER.debug("com.codahale.metrics.MetricRegistry not found, generating stub");
ClassPool classPool = new ClassPool();
classPool.appendClassPath(new LoaderClassPath(this.getClass().getClassLoader()));
try {
CtClass targetCt = classPool.makeClass("com.codahale.metrics.MetricRegistry");
targetCt.setModifiers(Modifier.PUBLIC | Modifier.FINAL);
CtConstructor constructorCt = new CtConstructor(null, targetCt);
constructorCt.setModifiers(Modifier.PUBLIC);
constructorCt.setBody("{ throw new RuntimeException(\"HikariCP Codahale shim says: Codahale metrics library is required but was not found in the classpath\"); }");
targetCt.addConstructor(constructorCt);
targetCt.toClass(classPool.getClassLoader(), getClass().getProtectionDomain());
}
catch (CannotCompileException cce) {
LOGGER.error("Cannot generate CodaHale metrics shim", cce);
throw new RuntimeException(cce);
}
}
finally {
Thread.currentThread().setContextClassLoader(contextClassLoader);
}
}
}