/*
* Copyright 2002-2011 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.Set;
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;
/**
* Given a set of @{@link ExceptionHandler} methods at initialization, finds
* the best matching method mapped to an exception at runtime.
*
* <p>Exception mappings are extracted from the method @{@link ExceptionHandler}
* annotation or by looking for {@link Throwable} method arguments.
*
* @author Rossen Stoyanchev
* @since 3.1
*/
public class ExceptionHandlerMethodResolver {
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>();
private final Map<Class<? extends Throwable>, Method> exceptionLookupCache =
new ConcurrentHashMap<Class<? extends Throwable>, Method>();
/**
* A constructor that finds {@link ExceptionHandler} methods in a handler.
* @param handlerType the handler to inspect for exception handler methods.
* @throws IllegalStateException
* If an exception type is mapped to two methods.
* @throws IllegalArgumentException
* If an @{@link ExceptionHandler} method is not mapped to any exceptions.
*/
public ExceptionHandlerMethodResolver(Class<?> handlerType) {
init(HandlerMethodSelector.selectMethods(handlerType, EXCEPTION_HANDLER_METHODS));
}
private void init(Set<Method> exceptionHandlerMethods) {
for (Method method : exceptionHandlerMethods) {
for (Class<? extends Throwable> exceptionType : detectMappedExceptions(method)) {
addExceptionMapping(exceptionType, method);
}
}
}
/**
* Detect the exceptions an @{@link ExceptionHandler} method is mapped to.
* If the method @{@link ExceptionHandler} annotation doesn't have any,
* scan the method signature for all arguments of type {@link Throwable}.
*/
@SuppressWarnings("unchecked")
private List<Class<? extends Throwable>> detectMappedExceptions(Method method) {
List<Class<? extends Throwable>> result = new ArrayList<Class<? extends Throwable>>();
ExceptionHandler annotation = AnnotationUtils.findAnnotation(method, ExceptionHandler.class);
if (annotation != null) {
result.addAll(Arrays.asList(annotation.value()));
}
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;
}
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 + "}.");
}
}
/**
* Find a method to handle the given exception. If more than one match is
* found, the best match is selected via {@link ExceptionDepthComparator}.
* @param exception the exception
* @return an @{@link ExceptionHandler} method, or {@code null}
*/
public Method resolveMethod(Exception exception) {
Class<? extends Exception> exceptionType = exception.getClass();
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 method mapped to the exception type, or {@code null}.
*/
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 mappedMethods.get(matches.get(0));
}
else {
return null;
}
}
/**
* A filter for selecting @{@link ExceptionHandler} methods.
*/
public final static MethodFilter EXCEPTION_HANDLER_METHODS = new MethodFilter() {
public boolean matches(Method method) {
return AnnotationUtils.findAnnotation(method, ExceptionHandler.class) != null;
}
};
}