org.springframework.instrument.classloading.ResourceOverridingShadowingClassLoader Maven / Gradle / Ivy
/*
* Copyright 2002-2018 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
*
* https://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.springframework.instrument.classloading;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
/**
* Subclass of ShadowingClassLoader that overrides attempts to
* locate certain files.
*
* @author Rod Johnson
* @author Adrian Colyer
* @since 2.0
*/
public class ResourceOverridingShadowingClassLoader extends ShadowingClassLoader {
private static final Enumeration EMPTY_URL_ENUMERATION = new Enumeration() {
@Override
public boolean hasMoreElements() {
return false;
}
@Override
public URL nextElement() {
throw new UnsupportedOperationException("Should not be called. I am empty.");
}
};
/**
* Key is asked for value: value is actual value.
*/
private Map overrides = new HashMap<>();
/**
* Create a new ResourceOverridingShadowingClassLoader,
* decorating the given ClassLoader.
* @param enclosingClassLoader the ClassLoader to decorate
*/
public ResourceOverridingShadowingClassLoader(ClassLoader enclosingClassLoader) {
super(enclosingClassLoader);
}
/**
* Return the resource (if any) at the new path
* on an attempt to locate a resource at the old path.
* @param oldPath the path requested
* @param newPath the actual path to be looked up
*/
public void override(String oldPath, String newPath) {
this.overrides.put(oldPath, newPath);
}
/**
* Ensure that a resource with the given path is not found.
* @param oldPath the path of the resource to hide even if
* it exists in the parent ClassLoader
*/
public void suppress(String oldPath) {
this.overrides.put(oldPath, null);
}
/**
* Copy all overrides from the given ClassLoader.
* @param other the other ClassLoader to copy from
*/
public void copyOverrides(ResourceOverridingShadowingClassLoader other) {
Assert.notNull(other, "Other ClassLoader must not be null");
this.overrides.putAll(other.overrides);
}
@Override
public URL getResource(String requestedPath) {
if (this.overrides.containsKey(requestedPath)) {
String overriddenPath = this.overrides.get(requestedPath);
return (overriddenPath != null ? super.getResource(overriddenPath) : null);
}
else {
return super.getResource(requestedPath);
}
}
@Override
@Nullable
public InputStream getResourceAsStream(String requestedPath) {
if (this.overrides.containsKey(requestedPath)) {
String overriddenPath = this.overrides.get(requestedPath);
return (overriddenPath != null ? super.getResourceAsStream(overriddenPath) : null);
}
else {
return super.getResourceAsStream(requestedPath);
}
}
@Override
public Enumeration getResources(String requestedPath) throws IOException {
if (this.overrides.containsKey(requestedPath)) {
String overriddenLocation = this.overrides.get(requestedPath);
return (overriddenLocation != null ?
super.getResources(overriddenLocation) : EMPTY_URL_ENUMERATION);
}
else {
return super.getResources(requestedPath);
}
}
}