javax.el.FactoryFinder Maven / Gradle / Ivy
/*
* Copyright (c) 1997-2018 Oracle and/or its affiliates and others.
* All rights reserved.
* Copyright 2004 The Apache Software Foundation
*
* 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 javax.el;
import static java.io.File.separator;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.lang.reflect.Constructor;
import java.util.Properties;
class FactoryFinder {
/**
* Creates an instance of the specified class using the specified ClassLoader object.
*
* @exception ELException if the given class could not be found or could not be instantiated
*/
private static Object newInstance(String className, ClassLoader classLoader, Properties properties) {
try {
Class spiClass;
if (classLoader == null) {
spiClass = Class.forName(className);
} else {
spiClass = classLoader.loadClass(className);
}
if (properties != null) {
Constructor constr = null;
try {
constr = spiClass.getConstructor(Properties.class);
} catch (Exception ex) {
}
if (constr != null) {
return constr.newInstance(properties);
}
}
return spiClass.newInstance();
} catch (ClassNotFoundException x) {
throw new ELException("Provider " + className + " not found", x);
} catch (Exception x) {
throw new ELException("Provider " + className + " could not be instantiated: " + x, x);
}
}
/**
* Finds the implementation Class object for the given factory name, or if that fails, finds the
* Class object for the given fallback class name. The arguments supplied must be used in order. If using
* the first argument is successful, the second one will not be used.
*
* This method is package private so that this code can be shared.
*
* @return the Class object of the specified message factory; may not be null
*
* @param factoryId the name of the factory to find, which is a system property
* @param fallbackClassName the implementation class name, which is to be used only if nothing else is found;
* null to indicate that there is no fallback class name
* @exception ELException if there is an error
*/
static Object find(String factoryId, String fallbackClassName, Properties properties) {
ClassLoader classLoader;
try {
classLoader = Thread.currentThread().getContextClassLoader();
} catch (Exception x) {
throw new ELException(x.toString(), x);
}
String serviceId = "META-INF/services/" + factoryId;
// try to find services in CLASSPATH
try {
InputStream is = null;
if (classLoader == null) {
is = ClassLoader.getSystemResourceAsStream(serviceId);
} else {
is = classLoader.getResourceAsStream(serviceId);
}
if (is != null) {
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
String factoryClassName = reader.readLine();
reader.close();
if (factoryClassName != null && !"".equals(factoryClassName)) {
return newInstance(factoryClassName, classLoader, properties);
}
}
} catch (Exception ex) {
}
// Try to read from $java.home/lib/el.properties
try {
String javah = System.getProperty("java.home");
String configFileName = javah + separator + "lib" + separator + "el.properties";
File configFile = new File(configFileName);
if (configFile.exists()) {
Properties props = new Properties();
props.load(new FileInputStream(configFile));
String factoryClassName = props.getProperty(factoryId);
return newInstance(factoryClassName, classLoader, properties);
}
} catch (Exception ex) {
}
// Use the system property
try {
String systemProp = System.getProperty(factoryId);
if (systemProp != null) {
return newInstance(systemProp, classLoader, properties);
}
} catch (SecurityException se) {
}
if (fallbackClassName == null) {
throw new ELException("Provider for " + factoryId + " cannot be found", null);
}
return newInstance(fallbackClassName, classLoader, properties);
}
}