主要是通过实例来分析
前台代码
<!--
模拟修改操作
1. 原始数据为: 1, Tom, 123456,tom@atguigu.com,12
2. 密码不能被修改.
3. 表单回显, 模拟操作直接在表单填写对应的属性值
-->
<form action="mvc/testModelAttribute" method="Post">
<input type="hidden" name="id" value="1"/>
username: <input type="text" name="username" value="Tom"/>
<br>
email: <input type="text" name="email" value="tom@atguigu.com"/>
<br>
age: <input type="text" name="age" value="12"/>
<br>
<input type="submit" value="Submit"/>
</form>
后台代码
/**
* 测试@ModelAndAttribute注解
*/
@RequestMapping("/testModelAttribute")
public String testModelAttribute(@ModelAttribute("abc") User user){
System.out.println("修改： " + user);
return SUCCESS ;
}
/**
* 被@ModelAttribute标记的方法,在执行之前都会执行此方法
*/
@ModelAttribute
public void getUser(@RequestParam(value="id",required=false)Integer id,
Map<String,Object> map){
if(id != null ){
// 模拟从数据库中获取对象
User user = new User("Tom", "123456", "tom@qq.com", 12);
user.setId(1);
System.out.println("从数据库中获取一个对象:" + user);
map.put("efg", user);
}
}
分析
通过debug调试,我们知道被@ModelAttribute注解修饰的方法执行在每个方法的前面
//HandlerMethodInvoker map.put("efg", user);方法执行之前
public final Object invokeHandlerMethod(Method handlerMethod, Object handler,
NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception {
//SpringMVCTest 此行代码打了断点
map.put("efg", user);
//遍历每个被 @ModelAttributeMethods注解修饰的 方法
for (Method attributeMethod : this.methodResolver.getModelAttributeMethods()) {
Method attributeMethodToInvoke = BridgeMethodResolver.findBridgedMethod(attributeMethod);
Object[] args = resolveHandlerArguments(attributeMethodToInvoke, handler, webRequest, implicitModel);
if (debug) {
logger.debug("Invoking model attribute method: " + attributeMethodToInvoke);
}
String attrName = AnnotationUtils.findAnnotation(attributeMethod, ModelAttribute.class).value();
if (!"".equals(attrName) && implicitModel.containsAttribute(attrName)) {
continue;
}
ReflectionUtils.makeAccessible(attributeMethodToInvoke);
// 在执行这行代码的时候又回到SpringMVCTest3中执行map.put("efg", user);
// 将map中的数据封装到implicitModel中,implicitModel是BingAwareModelMap类型,键值分别是map传入的键值
//此时的implicitModel：{efg=User [username=Tom, password=123456, email=tom@qq.com, age=12, address=null]}
Object attrValue = attributeMethodToInvoke.invoke(handler, args);
if ("".equals(attrName)) {
Class<?> resolvedType = GenericTypeResolver.resolveReturnType(attributeMethodToInvoke, handler.getClass());
attrName = Conventions.getVariableNameForReturnType(attributeMethodToInvoke, resolvedType, attrValue);
}
if (!implicitModel.containsAttribute(attrName)) {
implicitModel.addAttribute(attrName, attrValue);
}
}
// ...
// 核心代码,这里进行复制操作
Object[] args = resolveHandlerArguments(handlerMethodToInvoke, handler, webRequest, implicitModel);
if (debug) {
logger.debug("Invoking request handler method: " + handlerMethodToInvoke);
}
ReflectionUtils.makeAccessible(handlerMethodToInvoke);
// 回到SpringMVCTest3中执行testModelAttribute方法
return handlerMethodToInvoke.invoke(handler, args);
进入到resolveHandlerArguments方法
//...
// 这里看核心代码
else if (attrName != null) {
// 创建WebDataBinder对象,具体创建过程查看下面分析
WebDataBinder binder =
resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler);
boolean assignBindingResult = (args.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1]));
if (binder.getTarget() != null) {
// 这里完成对数据的存放,request中
doBind(binder, webRequest, validate, validationHints, !assignBindingResult);
}
args[i] = binder.getTarget();
if (assignBindingResult) {
args[i + 1] = binder.getBindingResult();
i++;
}
implicitModel.putAll(binder.getBindingResult().getModel());
}
}
return args;
private WebDataBinder resolveModelAttribute(String attrName, MethodParameter methodParam,
ExtendedModelMap implicitModel, NativeWebRequest webRequest, Object handler) throws Exception {
// Bind request parameter onto object...
String name = attrName; // abc
if ("".equals(name)) { // 如果name为""的话,则SpringMVC默认使用类名首字母小写作为name
name = Conventions.getVariableNameForParameter(methodParam);
}
// 获取参数类型,此处是User类型
Class<?> paramType = methodParam.getParameterType();
Object bindObject;
// 查看implicitModel的键是否有abc,由上面分析可知implicitModel只有def因此此处不执行
if (implicitModel.containsKey(name)) {
bindObject = implicitModel.get(name);
}
// 查看当前类是否添加了@SessionAttribute注解
// 若使用了该注解, 且 @SessionAttributes 注解的 value 属性值中包含了@ModelAndAttribute中的value(添加了@ModelAndAttribute注解的情况)/类名首字母小写(没有添加@ModelAndAttribute注解的情况),这里就简称key.
// 则会从 HttpSession 中来获取 key 所对应的 User对象, 若存在则直接传入到目标方法的入参中. 若不存在则将抛出异常.当前例子也不会进行
else if (this.methodResolver.isSessionAttribute(name, paramType)) {
bindObject = this.sessionAttributeStore.retrieveAttribute(webRequest, name);
if (bindObject == null) {
raiseSessionRequiredException("Session attribute '" + name + "' required - not found in session");
}
}
else {
// 进入到这里,利用反射创建一个新对象
bindObject = BeanUtils.instantiateClass(paramType);
}
// 创建WebDataBinder,createBinder(webRequest, bindObject, name)下面分析
WebDataBinder binder = createBinder(webRequest, bindObject, name);
initBinder(handler, name, binder, webRequest);
return binder;
}
createBinder(webRequest, bindObject, name)
protected WebDataBinder createBinder(NativeWebRequest webRequest, Object target, String objectName)
throws Exception {
return new WebRequestDataBinder(target, objectName);
}
public WebRequestDataBinder(Object target, String objectName) {
super(target, objectName);
}
//跟踪到DatBinder类中
public DataBinder(Object target, String objectName) {
// target:就是之前利用反射创建的User对象
// objectName:abc
if (target != null && target.getClass() == javaUtilOptionalClass) {
this.target = OptionalUnwrapper.unwrap(target);
}
else {
this.target = target;
}
this.objectName = objectName;
}
Ok,这样binder就创建完成了,再次把代码放大到下面中
//已经执行完成
WebDataBinder binder =
resolveModelAttribute(attrName, methodParam, implicitModel, webRequest, handler);
boolean assignBindingResult = (args.length > i + 1 && Errors.class.isAssignableFrom(paramTypes[i + 1]));
// 这个target为新建的User对象,因此进入doBinder()方法
if (binder.getTarget() != null) {
// 完成对象的复制操作,将前台传递过来的用户信息全部复制到新利用反射创建的对象中
doBind(binder, webRequest, validate, validationHints, !assignBindingResult);
}
args[i] = binder.getTarget();
if (assignBindingResult) {
args[i + 1] = binder.getBindingResult();
i++;
}
// 重新将abc-User对象的map添加到implicitModel中,此时implicitModel有两个map了,键值分别是abc和efg
implicitModel.putAll(binder.getBindingResult().getModel());
不配置产生的问题
// 问题一、当使用<mvc:view-controller path="/success" view-name="success"/>来实现直接访问页面的时候,@RequestMapping将会失去作用
// 问题二、当使用<mvc:default-servlet-handler/>来解决静态资源访问的问题的时候,@RequestMapping将会失去作用将会失去作用
// 问题三、当想实现类型的转换和数据的校验的时候需要配置,此时convertService为null
实验一 当mvc:default-servlet-handler/和<mvc:annotation-driven ></mvc:annotation-driven> 都没有配置时,conversionService为null ,此时DispatchServlet 的handleAdapter 情况如下：
HttpRequestHandleAdapter
SimpleControllerHandlerAdapter
AnnotationMethodHandlerAdater
当有mvc:default-servlet-handler/还有<mvc:annotation-driven ></mvc:annotation-driven> conversionService不为null ,此时DispatchServlet情况如下：
HttpRequestHandlerAdater
SimpleControllerHandlerAdapter
此时少了一个注解方法处理适配器,不能处理被@RequestMapping注解修饰的类
当有mvc:default-servlet-handler/但是没有<mvc:annotation-driven ></mvc:annotation-driven> conversionService不为null ,此时DispatchServlet情况如下：
HttpRequestHandlerAdater
SimpleControllerHandlerAdapter
RequestMappingHandlerAdapter
可以对WebDataBinder进行初始化. **注意:**方法不能有返回值,申明必须是void @InitBinder方法参数是WebDataBinder
// 对象的复制(前台数据传递到后台)和下面操作都是在
//resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory)
// 方法中进行
@InitBinder
public void initBinder(WebDataBinder binder){
binder.setDisallowedFields("lastName");
}
实现步骤
- 1、xml中注册CommonsMultipartResolver,id必须为multipartResolver
- 2、Java代码中使用MultipartFile 类型变量接收
实例
xml：
<!--
文件上传MultipartResolver
需要注意的是：文件名必须是multipartResolver,否则springmvc找不到multipartResolver
-->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<property name="defaultEncoding" value="utf-8"></property>
<property name="maxUploadSize" value="102400"></property>
</bean>
/*********************************************************************/
java:
/**
* 测试文件上传
*/
@RequestMapping(value = "/testFileUpload")
public String testFileUpload(@RequestParam(value="desc",required=false)String desc,
@RequestParam("file") MultipartFile file){
System.out.println("desc:" + desc );
System.out.println("文件名：" + file.getOriginalFilename());
return SUCCESS ;
}
源码分析
首先,服务器一启动,就会加载springmvc配置文件,即会创建CommonsMultipartResolver对象,接着在DispatcherServlet进行初始化
/** Well-known name for the MultipartResolver object in the bean factory for this namespace. */
public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
private void initMultipartResolver(ApplicationContext context) {
try {
// 从context中通过指定id获取multipartResolver对象,MULTIPART_RESOLVER_BEAN_NAME其实就是multipartResolver
// 因此,我们在springmvc.xml中配置只能这样指定
this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
if (logger.isDebugEnabled()) {
logger.debug("Using MultipartResolver [" + this.multipartResolver + "]");
}
}
catch (NoSuchBeanDefinitionException ex) {
// Default is no multipart resolver.
this.multipartResolver = null;
if (logger.isDebugEnabled()) {
logger.debug("Unable to locate MultipartResolver with name '" + MULTIPART_RESOLVER_BEAN_NAME +
"': no multipart request handling provided");
}
}
}
只要我们配置了如下注解,springmvc就会为其配置ExceptionHandlerExceptionResolver处理类.如果没有配置的话,则使用AnnotationMethodHandlerExceptionResolver(过时)
<mvc:annotation-driven/>
Controller异常处理
/**
* 1、处理异常,异常处理是有优先级的,默认先找被精确度高的注解修饰的方法
* 如果想要把异常信息输出的页面上,则可以使用ModelAndView,不可以使用
* Map进行封装(会报错)
* 2、如果当前Controller中没有找到对应的异常处理方法,springmvc则会去
* 找被@ControllerAdvice注解修饰的类中查找
*/
@ExceptionHandler({ArithmeticException.class})
public ModelAndView handleMathException(Exception ex){
ModelAndView mv = new ModelAndView("error");
mv.addObject("ex", ex.getMessage());
return mv ;
}
全局异常处理
@ControllerAdvice
public class HandlerException {
@ExceptionHandler({ArithmeticException.class})
public ModelAndView handleMathException(Exception ex){
ModelAndView mv = new ModelAndView("error");
mv.addObject("ex", ex);
return mv ;
}
}
ResponseStatusExceptionResolver
// 这个注解的功能：
//我们可以自己来定制状态码和状态原因
@ResponseStatus(reason="用户名不能为null",code=HttpStatus.FORBIDDEN)
public class UserNameException extends RuntimeException {
/**
*
*/
private static final long serialVersionUID = 1L;
}
DefaultHandlerExceptionResolver
这个类主要处理一些spring的异常,具体解释如下:
Default implementation of the {@link org.springframework.web.servlet.HandlerExceptionResolver
HandlerExceptionResolver} interface that resolves standard Spring exceptions and translates
them to corresponding HTTP status codes.
SimpleMappingExceptionResolver
这个主要是在xml中配置,如下,和ExceptionHandlerExceptionResolver不同的是,springmvc会将 异常信息自动的封装到request域中,默认为exception.
<bean class="org.springframework.web.servlet.handler.SimpleMappingExceptionResolver">
<!-- 放入request域的属性名 -->
<property name="exceptionAttribute" value="ex"></property>
<property name="exceptionMappings">
<props>
<prop key="java.lang.ArrayIndexOutOfBoundsException">error</prop>
</props>
</property>
</bean>
源码如下：
public static final String DEFAULT_EXCEPTION_ATTRIBUTE = "exception";
// 通过修改这个属性来修改异常存入request的键值
private String exceptionAttribute = DEFAULT_EXCEPTION_ATTRIBUTE;
@Override
protected ModelAndView doResolveException(HttpServletRequest request, HttpServletResponse response,
Object handler, Exception ex) {
// Expose ModelAndView for chosen error view.
String viewName = determineViewName(ex, request);
if (viewName != null) {
// Apply HTTP status code for error views, if specified.
// Only apply it if we're processing a top-level request.
Integer statusCode = determineStatusCode(request, viewName);
if (statusCode != null) {
applyStatusCodeIfPossible(request, response, statusCode);
}
return getModelAndView(viewName, ex, request);
}
else {
return null;
}
}
protected ModelAndView getModelAndView(String viewName, Exception ex, HttpServletRequest request) {
return getModelAndView(viewName, ex);
}
protected ModelAndView getModelAndView(String viewName, Exception ex) {
ModelAndView mv = new ModelAndView(viewName);
if (this.exceptionAttribute != null) {
if (logger.isDebugEnabled()) {
logger.debug("Exposing Exception as model attribute '" + this.exceptionAttribute + "'");
}
mv.addObject(this.exceptionAttribute, ex);
}
return mv;
}
-
1、按照web.xml中DispatchServlet的url-pattern拦截请求, 在springmvc找查找是否有对应的映射
-
2 不存在对应的映射,择到springmvc.xml中查找是否有mvc:default-servlet-handler/标签 如果有则响应(一般是静态资源),如果没有,则报404,且控制台报No mapping found for http....
-
3 找到了对应的映射
源码分析
DispatcherServlet类
// doDispatch()方法中
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
// code ...
//mappedHandler:HandlerExecutionChain类型,包含了处理器对象和拦截器
// 通过HandlerMapping对象获取
mappedHandler = getHandler(processedRequest);
// code ...
// Determine handler adapter for the current request.
// HandlerAdapter:在调用目标方法之前封装的一些操作
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// code ...
// 调用拦截器的Handle方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// code ...
// Actually invoke the handler.
// 调用目标方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
// code ...
// 调用拦截器的postHandle方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
// code ...
// 处理视图
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// HandlerMapping:请求和处理器之间的映射
// 当没有配置时,handlerMappings有两个
//org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping@66f28a1f,
// 这个类是一个过时类
//org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping@ae73c80
//当配置了<mvc:annotation-driven></mvc:annotation-driven>标签页是两个
//org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping@4da39ca9,
//org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping@6db328f8
// 当配置了<mvc:annotation-driven></mvc:annotation-driven>和<mvc:default-servlet-handler/>有三个
//org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping@485caa8f,
//org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping@12c0c0b3,
// 这个主要解决静态资源的访问的
//org.springframework.web.servlet.handler.SimpleUrlHandlerMapping@239f017e
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
// 处理异常
// code ...
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
// 渲染视图
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
// 调用拦截器的afterCompletion方法
mappedHandler.triggerAfterCompletion(request, response, null);
}
HandlerExecutionChain类
// 拦截器的preHandle方法
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}