/*
* Copyright 2002-2014 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.springframework.web.method.annotation;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.springframework.core.ExceptionDepthComparator;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ReflectionUtils.MethodFilter;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.method.HandlerMethodSelector;
/**
* Discovers {@linkplain ExceptionHandler @ExceptionHandler} methods in a given class,
* including all of its superclasses, and helps to resolve a given {@link Exception}
* to the exception types supported by a given {@link Method}.
*
* @author Rossen Stoyanchev
* @since 3.1
*/
public class ExceptionHandlerMethodResolver {
/**
* A filter for selecting {@code @ExceptionHandler} methods.
*/
public static final MethodFilter EXCEPTION_HANDLER_METHODS = new MethodFilter() {
@Override
public boolean matches(Method method) {
return (AnnotationUtils.findAnnotation(method, ExceptionHandler.class) != null);
}
};
/**
* Arbitrary {@link Method} reference, indicating no method found in the cache.
*/
private static final Method NO_METHOD_FOUND = ClassUtils.getMethodIfAvailable(System.class, "currentTimeMillis");
private final Map<Class<? extends Throwable>, Method> mappedMethods =
new ConcurrentHashMap<Class<? extends Throwable>, Method>(16);
private final Map<Class<? extends Throwable>, Method> exceptionLookupCache =
new ConcurrentHashMap<Class<? extends Throwable>, Method>(16);
/**
* A constructor that finds {@link ExceptionHandler} methods in the given type.
* @param handlerType the type to introspect
*/
public ExceptionHandlerMethodResolver(Class<?> handlerType) {
for (Method method : HandlerMethodSelector.selectMethods(handlerType, EXCEPTION_HANDLER_METHODS)) {
for (Class<? extends Throwable> exceptionType : detectExceptionMappings(method)) {
addExceptionMapping(exceptionType, method);
}
}
}
/**
* Extract exception mappings from the {@code @ExceptionHandler} annotation first,
* and then as a fallback from the method signature itself.
*/
@SuppressWarnings("unchecked")
private List<Class<? extends Throwable>> detectExceptionMappings(Method method) {
List<Class<? extends Throwable>> result = new ArrayList<Class<? extends Throwable>>();
detectAnnotationExceptionMappings(method, result);
if (result.isEmpty()) {
for (Class<?> paramType : method.getParameterTypes()) {
if (Throwable.class.isAssignableFrom(paramType)) {
result.add((Class<? extends Throwable>) paramType);
}
}
}
Assert.notEmpty(result, "No exception types mapped to {" + method + "}");
return result;
}
protected void detectAnnotationExceptionMappings(Method method, List<Class<? extends Throwable>> result) {
ExceptionHandler annot = AnnotationUtils.findAnnotation(method, ExceptionHandler.class);
result.addAll(Arrays.asList(annot.value()));
}
private void addExceptionMapping(Class<? extends Throwable> exceptionType, Method method) {
Method oldMethod = this.mappedMethods.put(exceptionType, method);
if (oldMethod != null && !oldMethod.equals(method)) {
throw new IllegalStateException(
"Ambiguous @ExceptionHandler method mapped for [" + exceptionType + "]: {" +
oldMethod + ", " + method + "}.");
}
}
/**
* Whether the contained type has any exception mappings.
*/
public boolean hasExceptionMappings() {
return !this.mappedMethods.isEmpty();
}
/**
* Find a {@link Method} to handle the given exception.
* Use {@link ExceptionDepthComparator} if more than one match is found.
* @param exception the exception
* @return a Method to handle the exception, or {@code null} if none found
*/
public Method resolveMethod(Exception exception) {
return resolveMethodByExceptionType(exception.getClass());
}
/**
* Find a {@link Method} to handle the given exception type. This can be
* useful if an {@link Exception} instance is not available (e.g. for tools).
* @param exceptionType the exception type
* @return a Method to handle the exception, or {@code null} if none found
*/
public Method resolveMethodByExceptionType(Class<? extends Exception> exceptionType) {
Method method = this.exceptionLookupCache.get(exceptionType);
if (method == null) {
method = getMappedMethod(exceptionType);
this.exceptionLookupCache.put(exceptionType, (method != null ? method : NO_METHOD_FOUND));
}
return (method != NO_METHOD_FOUND ? method : null);
}
/**
* Return the {@link Method} mapped to the given exception type, or {@code null} if none.
*/
private Method getMappedMethod(Class<? extends Exception> exceptionType) {
List<Class<? extends Throwable>> matches = new ArrayList<Class<? extends Throwable>>();
for (Class<? extends Throwable> mappedException : this.mappedMethods.keySet()) {
if (mappedException.isAssignableFrom(exceptionType)) {
matches.add(mappedException);
}
}
if (!matches.isEmpty()) {
Collections.sort(matches, new ExceptionDepthComparator(exceptionType));
return this.mappedMethods.get(matches.get(0));
}
else {
return null;
}
}
}