实现跨域请求jsonp方式

原理：http://madong.net.cn/index.php/2012/12/368/

调用端：

$.getJSON("http://192.168.220.85:8001/esb/autocredit/test?callback=?",function(data){
alert(data);
});

服务端:（基于spring mvc  @RestController 或 @ResponseBody注解）

更改源码:ServletInvocableHandlerMethod.java

主要添加:

---------------------------------------------

String parameter = webRequest.getParameter("callback");
if (parameter != null) {
returnValue = parameter + "(" + returnValue.toString() + ")";
}

---------------------------------------------

/*
* Copyright 2002-2012 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.springframework.web.servlet.mvc.method.annotation;

import java.io.IOException;
import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.concurrent.Callable;

import org.springframework.http.HttpStatus;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.context.request.ServletWebRequest;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite;
import org.springframework.web.method.support.InvocableHandlerMethod;
import org.springframework.web.method.support.ModelAndViewContainer;
import org.springframework.web.servlet.View;
import org.springframework.web.util.NestedServletException;

/**
* Extends {@link InvocableHandlerMethod} with the ability to handle return
* values through a registered {@link HandlerMethodReturnValueHandler} and also
* supports setting the response status based on a method-level
* {@code @ResponseStatus} annotation.
*
* <p>
* A {@code null} return value (including void) may be interpreted as the end of
* request processing in combination with a {@code @ResponseStatus} annotation,
* a not-modified check condition (see
* {@link ServletWebRequest#checkNotModified(long)}), or a method argument that
* provides access to the response stream.
*
* @author Rossen Stoyanchev
* @since 3.1
*/
public class ServletInvocableHandlerMethod extends InvocableHandlerMethod {

private HttpStatus responseStatus;

private String responseReason;

private HandlerMethodReturnValueHandlerComposite returnValueHandlers;

/**
* Creates an instance from the given handler and method.
*/
public ServletInvocableHandlerMethod(Object handler, Method method) {
super(handler, method);
initResponseStatus();
}

/**
* Create an instance from a {@code HandlerMethod}.
*/
public ServletInvocableHandlerMethod(HandlerMethod handlerMethod) {
super(handlerMethod);
initResponseStatus();
}

private void initResponseStatus() {
ResponseStatus annot = getMethodAnnotation(ResponseStatus.class);
if (annot != null) {
this.responseStatus = annot.value();
this.responseReason = annot.reason();
}
}

/**
* Register {@link HandlerMethodReturnValueHandler} instances to use to
* handle return values.
*/
public void setHandlerMethodReturnValueHandlers(HandlerMethodReturnValueHandlerComposite returnValueHandlers) {
this.returnValueHandlers = returnValueHandlers;
}

/**
* Invokes the method and handles the return value through a registered
* {@link HandlerMethodReturnValueHandler}.
*
* @param webRequest
* the current request
* @param mavContainer
* the ModelAndViewContainer for this request
* @param providedArgs
* "given" arguments matched by type, not resolved
*/
public final void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception {

Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);

// 为实现跨域请求 添加实现 add by x
String parameter = webRequest.getParameter("callback");
if (parameter != null) {
returnValue = parameter + "(" + returnValue.toString() + ")";
}
// 为实现跨域请求 添加实现 add by x

setResponseStatus(webRequest);

if (returnValue == null) {
if (isRequestNotModified(webRequest) || hasResponseStatus() || mavContainer.isRequestHandled()) {
mavContainer.setRequestHandled(true);
return;
}
} else if (StringUtils.hasText(this.responseReason)) {
mavContainer.setRequestHandled(true);
return;
}

mavContainer.setRequestHandled(false);

try {
this.returnValueHandlers.handleReturnValue(returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
} catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(getReturnValueHandlingErrorMessage("Error handling return value", returnValue), ex);
}
throw ex;
}
}

/**
* Set the response status according to the {@link ResponseStatus}
* annotation.
*/
private void setResponseStatus(ServletWebRequest webRequest) throws IOException {
if (this.responseStatus == null) {
return;
}

if (StringUtils.hasText(this.responseReason)) {
webRequest.getResponse().sendError(this.responseStatus.value(), this.responseReason);
} else {
webRequest.getResponse().setStatus(this.responseStatus.value());
}

// to be picked up by the RedirectView
webRequest.getRequest().setAttribute(View.RESPONSE_STATUS_ATTRIBUTE, this.responseStatus);
}

/**
* Does the given request qualify as "not modified"?
*
* @see ServletWebRequest#checkNotModified(long)
* @see ServletWebRequest#checkNotModified(String)
*/
private boolean isRequestNotModified(ServletWebRequest webRequest) {
return webRequest.isNotModified();
}

/**
* Does this method have the response status instruction?
*/
private boolean hasResponseStatus() {
return responseStatus != null;
}

private String getReturnValueHandlingErrorMessage(String message, Object returnValue) {
StringBuilder sb = new StringBuilder(message);
if (returnValue != null) {
sb.append(" [type=" + returnValue.getClass().getName() + "] ");
}
sb.append("[value=" + returnValue + "]");
return getDetailedErrorMessage(sb.toString());
}

/**
* Create a ServletInvocableHandlerMethod that will return the given value
* from an async operation instead of invoking the controller method again.
* The async result value is then either processed as if the controller
* method returned it or an exception is raised if the async result value
* itself is an Exception.
*/
ServletInvocableHandlerMethod wrapConcurrentResult(final Object result) {

return new CallableHandlerMethod(new Callable<Object>() {

@Override
public Object call() throws Exception {
if (result instanceof Exception) {
throw (Exception) result;
} else if (result instanceof Throwable) {
throw new NestedServletException("Async processing failed", (Throwable) result);
}
return result;
}
});
}

/**
* A sub-class of {@link HandlerMethod} that invokes the given
* {@link Callable} instead of the target controller method. This is useful
* for resuming processing with the result of an async operation. The goal
* is to process the value returned from the Callable as if it was returned
* by the target controller method, i.e. taking into consideration both
* method and type-level controller annotations (e.g. {@code @ResponseBody},
* {@code @ResponseStatus}, etc).
*/
private class CallableHandlerMethod extends ServletInvocableHandlerMethod {

public CallableHandlerMethod(Callable<?> callable) {
super(callable, ClassUtils.getMethod(callable.getClass(), "call"));
this.setHandlerMethodReturnValueHandlers(ServletInvocableHandlerMethod.this.returnValueHandlers);
}

/**
* Bridge to type-level annotations of the target controller method.
*/
@Override
public Class<?> getBeanType() {
return ServletInvocableHandlerMethod.this.getBeanType();
}

/**
* Bridge to method-level annotations of the target controller method.
*/
@Override
public <A extends Annotation> A getMethodAnnotation(Class<A> annotationType) {
return ServletInvocableHandlerMethod.this.getMethodAnnotation(annotationType);
}
}

}