/*
* Copyright 2009-2012 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 org.apache.ibatis.io;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;
/**
* Provides a very simple API for accessing resources within an application server.
* 虚拟文件系统(VFS),用来读取服务器里的资源
*
* @author Ben Gunter
*/
public abstract class VFS {
private static final Log log = LogFactory.getLog(ResolverUtil.class);
/** The built-in implementations. */
//默认提供2个实现 JBoss6VFS,DefaultVFS
public static final Class<?>[] IMPLEMENTATIONS = { JBoss6VFS.class, DefaultVFS.class };
/** The list to which implementations are added by {@link #addImplClass(Class)}. */
//这里是提供一个用户扩展点，可以让用户自定义VFS实现
public static final List<Class<? extends VFS>> USER_IMPLEMENTATIONS = new ArrayList<Class<? extends VFS>>();
/** Singleton instance. */
private static VFS instance;
/**
* Get the singleton {@link VFS} instance. If no {@link VFS} implementation can be found for the
* current environment, then this method returns null.
*/
@SuppressWarnings("unchecked")
public static VFS getInstance() {
if (instance != null) {
return instance;
}
// Try the user implementations first, then the built-ins
List<Class<? extends VFS>> impls = new ArrayList<Class<? extends VFS>>();
impls.addAll(USER_IMPLEMENTATIONS);
impls.addAll(Arrays.asList((Class<? extends VFS>[]) IMPLEMENTATIONS));
// Try each implementation class until a valid one is found
//遍历查找实现类，返回第一个找到的
VFS vfs = null;
for (int i = 0; vfs == null || !vfs.isValid(); i++) {
Class<? extends VFS> impl = impls.get(i);
try {
vfs = impl.newInstance();
if (vfs == null || !vfs.isValid()) {
log.debug("VFS implementation " + impl.getName() +
" is not valid in this environment.");
}
} catch (InstantiationException e) {
log.error("Failed to instantiate " + impl, e);
return null;
} catch (IllegalAccessException e) {
log.error("Failed to instantiate " + impl, e);
return null;
}
}
log.debug("Using VFS adapter " + vfs.getClass().getName());
VFS.instance = vfs;
return VFS.instance;
}
/**
* Adds the specified class to the list of {@link VFS} implementations. Classes added in this
* manner are tried in the order they are added and before any of the built-in implementations.
*
* @param clazz The {@link VFS} implementation class to add.
*/
public static void addImplClass(Class<? extends VFS> clazz) {
if (clazz != null) {
USER_IMPLEMENTATIONS.add(clazz);
}
}
/** Get a class by name. If the class is not found then return null. */
protected static Class<?> getClass(String className) {
try {
return Thread.currentThread().getContextClassLoader().loadClass(className);
// return ReflectUtil.findClass(className);
} catch (ClassNotFoundException e) {
log.debug("Class not found: " + className);
return null;
}
}
/**
* Get a method by name and parameter types. If the method is not found then return null.
*
* @param clazz The class to which the method belongs.
* @param methodName The name of the method.
* @param parameterTypes The types of the parameters accepted by the method.
*/
protected static Method getMethod(Class<?> clazz, String methodName, Class<?>... parameterTypes) {
if (clazz == null) {
return null;
}
try {
return clazz.getMethod(methodName, parameterTypes);
} catch (SecurityException e) {
log.error("Security exception looking for method " + clazz.getName() + "." + methodName + ". Cause: " + e);
return null;
} catch (NoSuchMethodException e) {
log.error("Method not found " + clazz.getName() + "." + methodName + "." + methodName + ". Cause: " + e);
return null;
}
}
/**
* Invoke a method on an object and return whatever it returns.
*
* @param method The method to invoke.
* @param object The instance or class (for static methods) on which to invoke the method.
* @param parameters The parameters to pass to the method.
* @return Whatever the method returns.
* @throws IOException If I/O errors occur
* @throws StripesRuntimeException If anything else goes wrong
*/
@SuppressWarnings("unchecked")
protected static <T> T invoke(Method method, Object object, Object... parameters)
throws IOException, RuntimeException {
try {
return (T) method.invoke(object, parameters);
} catch (IllegalArgumentException e) {
throw new RuntimeException(e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
} catch (InvocationTargetException e) {
if (e.getTargetException() instanceof IOException) {
throw (IOException) e.getTargetException();
} else {
throw new RuntimeException(e);
}
}
}
/**
* Get a list of {@link URL}s from the context classloader for all the resources found at the
* specified path.
*
* @param path The resource path.
* @return A list of {@link URL}s, as returned by {@link ClassLoader#getResources(String)}.
* @throws IOException If I/O errors occur
*/
protected static List<URL> getResources(String path) throws IOException {
return Collections.list(Thread.currentThread().getContextClassLoader().getResources(path));
}
/** Return true if the {@link VFS} implementation is valid for the current environment. */
public abstract boolean isValid();
/**
* Recursively list the full resource path of all the resources that are children of the
* resource identified by a URL.
*
* @param url The URL that identifies the resource to list.
* @param forPath The path to the resource that is identified by the URL. Generally, this is the
* value passed to {@link #getResources(String)} to get the resource URL.
* @return A list containing the names of the child resources.
* @throws IOException If I/O errors occur
*/
protected abstract List<String> list(URL url, String forPath) throws IOException;
/**
* Recursively list the full resource path of all the resources that are children of all the
* resources found at the specified path.
*
* @param path The path of the resource(s) to list.
* @return A list containing the names of the child resources.
* @throws IOException If I/O errors occur
*/
public List<String> list(String path) throws IOException {
List<String> names = new ArrayList<String>();
for (URL url : getResources(path)) {
names.addAll(list(url, path));
}
return names;
}
}