spring经典注解实例二 10分钟弄懂

昨天对Spring注解有了一个整体认识，至少完成了一个简单的web应用搭建。当然，还不完善，这仅仅只是个开始！
今天看了Spring 3.0的注解，我感觉自己被颠覆了。多年前，为了减少代码依赖我们用配置文件进行模块间耦合，降低模块之间的黏度。现如今，所有可配置的内容都塞进了代码中，我只能说：这多少有点顾此失彼，有点倒退的意思！使用注解的好处是：代码通读性增强。这既是优势也是劣势！如果我要改一段配置，就要打开代码逐行扫描；如果恰巧这是别人封装的jar包，那我只好反编译；如果碰巧遇上这个jar包经过了混淆，那我只好求助于AOP了。 为了这么一个配置，我的代码观几乎将要被颠覆！


言归正传，研究一下注解下的控制层。
我习惯于使用JSTL展示页面，因此需要在原lib基础上增加jstl.jar和standard.jar，详细lib依赖如下：

引用

aopalliance-1.0.jar
commons-logging-1.1.1.jar
log4j-1.2.15.jar
spring-beans-2.5.6.jar
spring-context-2.5.6.jar
spring-context-support-2.5.6.jar
spring-core-2.5.6.jar
spring-tx-2.5.6.jar
spring-web-2.5.6.jar
spring-webmvc-2.5.6.jar
standard.jar
jstl.jar


上一篇文中，我们定义了控制器AccountController：
AccountController.java

Java代码 
1./** 
2. * 2010-1-23 
3. */ 
4.package org.zlex.spring.controller;   
5. 
6.import javax.servlet.http.HttpServletRequest;   
7.import javax.servlet.http.HttpServletResponse;   
8. 
9.import org.springframework.beans.factory.annotation.Autowired;   
10.import org.springframework.stereotype.Controller;   
11.import org.springframework.web.bind.ServletRequestUtils;   
12.import org.springframework.web.bind.annotation.RequestMapping;   
13.import org.springframework.web.bind.annotation.RequestMethod;   
14.import org.zlex.spring.service.AccountService;   
15. 
16./** 
17. *  
18. * @author <a href="mailto:[e-mail]">梁栋</a> 
19. * @version 1.0 
20. * @since 1.0 
21. */ 
22.@Controller  
23.@RequestMapping("/account.do")   
24.public class AccountController {   
25. 
26.    @Autowired  
27.    private AccountService accountService;   
28. 
29.    @RequestMapping(method = RequestMethod.GET)   
30.    public void hello(HttpServletRequest request, HttpServletResponse response)   
31.            throws Exception {   
32. 
33.        String username = ServletRequestUtils.getRequiredStringParameter(  
34.                request, "username");   
35.        String password = ServletRequestUtils.getRequiredStringParameter(  
36.                request, "password");   
37.        System.out.println(accountService.verify(username, password));  
38.    }  
39.} 
Java代码
1./** 
2. * 2010-1-23 
3. */ 
4.package org.zlex.spring.controller;  
5. 
6.import javax.servlet.http.HttpServletRequest;  
7.import javax.servlet.http.HttpServletResponse;  
8. 
9.import org.springframework.beans.factory.annotation.Autowired;  
10.import org.springframework.stereotype.Controller;  
11.import org.springframework.web.bind.ServletRequestUtils;  
12.import org.springframework.web.bind.annotation.RequestMapping;  
13.import org.springframework.web.bind.annotation.RequestMethod;  
14.import org.zlex.spring.service.AccountService;  
15. 
16./** 
17. *  
18. * @author <a href="mailto:[e-mail]">梁栋</a> 
19. * @version 1.0 
20. * @since 1.0 
21. */ 
22.@Controller 
23.@RequestMapping("/account.do")  
24.public class AccountController {  
25. 
26.    @Autowired 
27.    private AccountService accountService;  
28. 
29.    @RequestMapping(method = RequestMethod.GET)  
30.    public void hello(HttpServletRequest request, HttpServletResponse response)  
31.            throws Exception {  
32. 
33.        String username = ServletRequestUtils.getRequiredStringParameter(  
34.                request, "username");  
35.        String password = ServletRequestUtils.getRequiredStringParameter(  
36.                request, "password");  
37.        System.out.println(accountService.verify(username, password));  
38.    }  
39.} 
/**
* 2010-1-23
*/
package org.zlex.spring.controller;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.ServletRequestUtils;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.zlex.spring.service.AccountService;

/**
*
* @author <a href="mailto:[e-mail]">梁栋</a>
* @version 1.0
* @since 1.0
*/
@Controller
@RequestMapping("/account.do")
public class AccountController {

@Autowired
private AccountService accountService;

@RequestMapping(method = RequestMethod.GET)
public void hello(HttpServletRequest request, HttpServletResponse response)
throws Exception {

String username = ServletRequestUtils.getRequiredStringParameter(
request, "username");
String password = ServletRequestUtils.getRequiredStringParameter(
request, "password");
System.out.println(accountService.verify(username, password));
}
}

先说注解@RequestMapping
这里使用注解@RequestMapping(method = RequestMethod.GET)指定这个方法为get请求时调用。同样，我们可以使用注解@RequestMapping(method = RequestMethod.POST)指定该方法接受post请求。

Java代码 
1.@Controller 
2.@RequestMapping("/account.do")   
3.public class AccountController {   
4. 
5.    @RequestMapping(method = RequestMethod.GET)   
6.    public void get() {   
7.    }  
8. 
9.    @RequestMapping(method = RequestMethod.POST)   
10.    public void post() {   
11.    }  
12.} 
Java代码
1.@Controller 
2.@RequestMapping("/account.do")  
3.public class AccountController {  
4. 
5.    @RequestMapping(method = RequestMethod.GET)  
6.    public void get() {  
7.    }  
8. 
9.    @RequestMapping(method = RequestMethod.POST)  
10.    public void post() {  
11.    }  
12.} 
@Controller
@RequestMapping("/account.do")
public class AccountController {

@RequestMapping(method = RequestMethod.GET)
public void get() {
}

@RequestMapping(method = RequestMethod.POST)
public void post() {
}
}

这与我们久别的Servlet很相像，类似于doGet()和doPost()方法！
我们也可以将其改造为多动作控制器，如下代码所示：

Java代码 
1.@Controller 
2.@RequestMapping("/account.do")   
3.public class AccountController {   
4. 
5.    @RequestMapping(params = "method=login")     
6.    public void login() {   
7.    }  
8. 
9.    @RequestMapping(params = "method=logout")     
10.    public void logout() {   
11.    } 
Java代码
1.@Controller 
2.@RequestMapping("/account.do")  
3.public class AccountController {  
4. 
5.    @RequestMapping(params = "method=login")    
6.    public void login() {  
7.    }  
8. 
9.    @RequestMapping(params = "method=logout")    
10.    public void logout() {  
11.    } 
@Controller
@RequestMapping("/account.do")
public class AccountController {

@RequestMapping(params = "method=login") 
public void login() {
}

@RequestMapping(params = "method=logout") 
public void logout() {
}

这样，我们可以通过参数“method”指定不同的参数值从而通过请求（"/account.do?method=login"和"/account.do?method=logout"）调用不同的方法！
注意：使用多动作控制器必须在配置文件中加入注解支持！

Xml代码 
1.<bean 
2.        class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />  
Xml代码
1.<bean 
2.        class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" /> 
<bean
class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />

当然，我们也可以将注解@RequestMapping指定到某一个方法上，如：

Java代码 
1.@Controller 
2.public class AccountController {   
3.      
4.    @RequestMapping("/a.do")   
5.    public void a() {}   
6. 
7.    @RequestMapping("/b.do")   
8.    public void b() {}   
9.} 
Java代码
1.@Controller 
2.public class AccountController {  
3.      
4.    @RequestMapping("/a.do")  
5.    public void a() {}  
6. 
7.    @RequestMapping("/b.do")  
8.    public void b() {}  
9.} 
@Controller
public class AccountController {

@RequestMapping("/a.do")
public void a() {}

@RequestMapping("/b.do")
public void b() {}
}

这样，请求“a.do”和“b.do”将对应不同的方法a() 和b()。这使得一个控制器可以同时承载多个请求！
@RequestMapping("/account.do")是@RequestMapping(value="/account.do")的简写！
再说输入参数！
这里的方法名可以随意定义，但是参数和返回值却又要求！
为什么？直接看源代码，我们就能找到答案！
AnnotationMethodHandlerAdapter.java部分源代码——有关参数部分：

Java代码 
1.@Override 
2.protected Object resolveStandardArgument(Class parameterType, NativeWebRequest webRequest)   
3.        throws Exception {   
4. 
5.    HttpServletRequest request = (HttpServletRequest) webRequest.getNativeRequest();  
6.    HttpServletResponse response = (HttpServletResponse) webRequest.getNativeResponse();  
7. 
8.    if (ServletRequest.class.isAssignableFrom(parameterType)) {   
9.        return request;   
10.    }  
11.    else if (ServletResponse.class.isAssignableFrom(parameterType)) {   
12.        this.responseArgumentUsed = true;   
13.        return response;   
14.    }  
15.    else if (HttpSession.class.isAssignableFrom(parameterType)) {   
16.        return request.getSession();   
17.    }  
18.    else if (Principal.class.isAssignableFrom(parameterType)) {   
19.        return request.getUserPrincipal();   
20.    }  
21.    else if (Locale.class.equals(parameterType)) {   
22.        return RequestContextUtils.getLocale(request);   
23.    }  
24.    else if (InputStream.class.isAssignableFrom(parameterType)) {   
25.        return request.getInputStream();   
26.    }  
27.    else if (Reader.class.isAssignableFrom(parameterType)) {   
28.        return request.getReader();   
29.    }  
30.    else if (OutputStream.class.isAssignableFrom(parameterType)) {   
31.        this.responseArgumentUsed = true;   
32.        return response.getOutputStream();   
33.    }  
34.    else if (Writer.class.isAssignableFrom(parameterType)) {   
35.        this.responseArgumentUsed = true;   
36.        return response.getWriter();   
37.    }  
38.    return super.resolveStandardArgument(parameterType, webRequest);   
39.} 
Java代码
1.@Override 
2.protected Object resolveStandardArgument(Class parameterType, NativeWebRequest webRequest)  
3.        throws Exception {  
4. 
5.    HttpServletRequest request = (HttpServletRequest) webRequest.getNativeRequest();  
6.    HttpServletResponse response = (HttpServletResponse) webRequest.getNativeResponse();  
7. 
8.    if (ServletRequest.class.isAssignableFrom(parameterType)) {  
9.        return request;  
10.    }  
11.    else if (ServletResponse.class.isAssignableFrom(parameterType)) {  
12.        this.responseArgumentUsed = true;  
13.        return response;  
14.    }  
15.    else if (HttpSession.class.isAssignableFrom(parameterType)) {  
16.        return request.getSession();  
17.    }  
18.    else if (Principal.class.isAssignableFrom(parameterType)) {  
19.        return request.getUserPrincipal();  
20.    }  
21.    else if (Locale.class.equals(parameterType)) {  
22.        return RequestContextUtils.getLocale(request);  
23.    }  
24.    else if (InputStream.class.isAssignableFrom(parameterType)) {  
25.        return request.getInputStream();  
26.    }  
27.    else if (Reader.class.isAssignableFrom(parameterType)) {  
28.        return request.getReader();  
29.    }  
30.    else if (OutputStream.class.isAssignableFrom(parameterType)) {  
31.        this.responseArgumentUsed = true;  
32.        return response.getOutputStream();  
33.    }  
34.    else if (Writer.class.isAssignableFrom(parameterType)) {  
35.        this.responseArgumentUsed = true;  
36.        return response.getWriter();  
37.    }  
38.    return super.resolveStandardArgument(parameterType, webRequest);  
39.} 
@Override
protected Object resolveStandardArgument(Class parameterType, NativeWebRequest webRequest)
throws Exception {

HttpServletRequest request = (HttpServletRequest) webRequest.getNativeRequest();
HttpServletResponse response = (HttpServletResponse) webRequest.getNativeResponse();

if (ServletRequest.class.isAssignableFrom(parameterType)) {
return request;
}
else if (ServletResponse.class.isAssignableFrom(parameterType)) {
this.responseArgumentUsed = true;
return response;
}
else if (HttpSession.class.isAssignableFrom(parameterType)) {
return request.getSession();
}
else if (Principal.class.isAssignableFrom(parameterType)) {
return request.getUserPrincipal();
}
else if (Locale.class.equals(parameterType)) {
return RequestContextUtils.getLocale(request);
}
else if (InputStream.class.isAssignableFrom(parameterType)) {
return request.getInputStream();
}
else if (Reader.class.isAssignableFrom(parameterType)) {
return request.getReader();
}
else if (OutputStream.class.isAssignableFrom(parameterType)) {
this.responseArgumentUsed = true;
return response.getOutputStream();
}
else if (Writer.class.isAssignableFrom(parameterType)) {
this.responseArgumentUsed = true;
return response.getWriter();
}
return super.resolveStandardArgument(parameterType, webRequest);
}

也就是说，如果我们想要在自定义的方法中获得一些个“标准”输入参数，参数类型必须包含在以下类型中：

引用

ServletRequest
ServletResponse
HttpSession
Principal
Locale
InputStream
OutputStream
Reader
Writer


当然，上述接口其实都是对于HttpServletRequest和HttpServletResponse的扩展。
此外，我们还可以定义自己的参数。
注意：自定义参数必须是实现类，绝非接口！Spring容器将帮你完成对象初始化工作！
比如说上文中，我们需要参数username和password。我们可以这么写：

Java代码 
1.@RequestMapping(method = RequestMethod.GET)  
2.public void hello(String username,String password) {   
3.    System.out.println(accountService.verify(username, password));  
4.} 
Java代码
1.@RequestMapping(method = RequestMethod.GET)  
2.public void hello(String username,String password) {  
3.    System.out.println(accountService.verify(username, password));  
4.} 
@RequestMapping(method = RequestMethod.GET)
public void hello(String username,String password) {
System.out.println(accountService.verify(username, password));
}

如果参数名不能与这里的变量名保持一致，那么我们可以使用注解@RequestParam进行强制绑定，代码如下所示：

Java代码 
1.@RequestMapping(method = RequestMethod.GET)  
2.public void hello(@RequestParam("username") String u,   
3.        @RequestParam("password") String p) {   
4.    System.out.println(accountService.verify(u, p));  
5.} 
Java代码
1.@RequestMapping(method = RequestMethod.GET)  
2.public void hello(@RequestParam("username") String u,  
3.        @RequestParam("password") String p) {  
4.    System.out.println(accountService.verify(u, p));  
5.} 
@RequestMapping(method = RequestMethod.GET)
public void hello(@RequestParam("username") String u,
@RequestParam("password") String p) {
System.out.println(accountService.verify(u, p));
}

这比起我们之前写的代码有所简洁：

Java代码 
1.@RequestMapping(method = RequestMethod.GET)  
2.public void hello(HttpServletRequest request, HttpServletResponse response)   
3.        throws Exception {   
4. 
5.    String username = ServletRequestUtils.getRequiredStringParameter(  
6.            request, "username");   
7.    String password = ServletRequestUtils.getRequiredStringParameter(  
8.            request, "password");   
9.    System.out.println(accountService.verify(username, password));  
10.} 
Java代码
1.@RequestMapping(method = RequestMethod.GET)  
2.public void hello(HttpServletRequest request, HttpServletResponse response)  
3.        throws Exception {  
4. 
5.    String username = ServletRequestUtils.getRequiredStringParameter(  
6.            request, "username");  
7.    String password = ServletRequestUtils.getRequiredStringParameter(  
8.            request, "password");  
9.    System.out.println(accountService.verify(username, password));  
10.} 
@RequestMapping(method = RequestMethod.GET)
public void hello(HttpServletRequest request, HttpServletResponse response)
throws Exception {

String username = ServletRequestUtils.getRequiredStringParameter(
request, "username");
String password = ServletRequestUtils.getRequiredStringParameter(
request, "password");
System.out.println(accountService.verify(username, password));
}

ServletRequestUtils类的工作已经由Spring底层实现了，我们只需要把参数名定义一致即可，其内部取参无需关心！
除了传入参数，我们还可以定义即将传出的参数，如加入ModelMap参数：

Java代码 
1.@SuppressWarnings("unchecked")  
2.@RequestMapping(method = RequestMethod.GET)   
3.public Map hello(String username, String password, ModelMap model) {   
4. 
5.    System.out.println(accountService.verify(username, password));  
6.      
7.    model.put("msg", username);   
8. 
9.    return model;   
10.} 
Java代码
1.@SuppressWarnings("unchecked")  
2.@RequestMapping(method = RequestMethod.GET)  
3.public Map hello(String username, String password, ModelMap model) {  
4. 
5.    System.out.println(accountService.verify(username, password));  
6.      
7.    model.put("msg", username);  
8. 
9.    return model;  
10.} 
@SuppressWarnings("unchecked")
@RequestMapping(method = RequestMethod.GET)
public Map hello(String username, String password, ModelMap model) {

System.out.println(accountService.verify(username, password));

model.put("msg", username);

return model;
}

这时，我们没有定义页面名称，Spring容器将根据请求名指定同名view，即如果是jap页面，则account.do->account.jsp！
不得不承认，这样写起来的确减少了代码量！
接着说输出参数！
通过ModelMap，我们可以绑定输出到的页面的参数，但最终我们将要返回到何种页面呢？再次查看AnnotationMethodHandlerAdapter源代码！
AnnotationMethodHandlerAdapter.java部分源代码——有关返回值部分：

Java代码 
1.@SuppressWarnings("unchecked")  
2.public ModelAndView getModelAndView(Method handlerMethod, Class handlerType, Object returnValue,   
3.        ExtendedModelMap implicitModel, ServletWebRequest webRequest) {  
4. 
5.    if (returnValue instanceof ModelAndView) {   
6.        ModelAndView mav = (ModelAndView) returnValue;  
7.        mav.getModelMap().mergeAttributes(implicitModel);  
8.        return mav;   
9.    }  
10.    else if (returnValue instanceof Model) {   
11.        return new ModelAndView().addAllObjects(implicitModel).addAllObjects(((Model) returnValue).asMap());   
12.    }  
13.    else if (returnValue instanceof Map) {   
14.        return new ModelAndView().addAllObjects(implicitModel).addAllObjects((Map) returnValue);   
15.    }  
16.    else if (returnValue instanceof View) {   
17.        return new ModelAndView((View) returnValue).addAllObjects(implicitModel);   
18.    }  
19.    else if (returnValue instanceof String) {   
20.        return new ModelAndView((String) returnValue).addAllObjects(implicitModel);   
21.    }  
22.    else if (returnValue == null) {   
23.        // Either returned null or was 'void' return.   
24.        if (this.responseArgumentUsed || webRequest.isNotModified()) {   
25.            return null;   
26.        }  
27.        else {   
28.            // Assuming view name translation...   
29.            return new ModelAndView().addAllObjects(implicitModel);   
30.        }  
31.    }  
32.    else if (!BeanUtils.isSimpleProperty(returnValue.getClass())) {   
33.        // Assume a single model attribute...   
34.        ModelAttribute attr = AnnotationUtils.findAnnotation(handlerMethod, ModelAttribute.class);   
35.        String attrName = (attr != null ? attr.value() : "");   
36.        ModelAndView mav = new ModelAndView().addAllObjects(implicitModel);   
37.        if ("".equals(attrName)) {   
38.            Class resolvedType = GenericTypeResolver.resolveReturnType(handlerMethod, handlerType);  
39.            attrName = Conventions.getVariableNameForReturnType(handlerMethod, resolvedType, returnValue);  
40.        }  
41.        return mav.addObject(attrName, returnValue);   
42.    }  
43.    else {   
44.        throw new IllegalArgumentException("Invalid handler method return value: " + returnValue);   
45.    }  
46.}  
Java代码
1.@SuppressWarnings("unchecked")  
2.public ModelAndView getModelAndView(Method handlerMethod, Class handlerType, Object returnValue,  
3.        ExtendedModelMap implicitModel, ServletWebRequest webRequest) {  
4. 
5.    if (returnValue instanceof ModelAndView) {  
6.        ModelAndView mav = (ModelAndView) returnValue;  
7.        mav.getModelMap().mergeAttributes(implicitModel);  
8.        return mav;  
9.    }  
10.    else if (returnValue instanceof Model) {  
11.        return new ModelAndView().addAllObjects(implicitModel).addAllObjects(((Model) returnValue).asMap());  
12.    }  
13.    else if (returnValue instanceof Map) {  
14.        return new ModelAndView().addAllObjects(implicitModel).addAllObjects((Map) returnValue);  
15.    }  
16.    else if (returnValue instanceof View) {  
17.        return new ModelAndView((View) returnValue).addAllObjects(implicitModel);  
18.    }  
19.    else if (returnValue instanceof String) {  
20.        return new ModelAndView((String) returnValue).addAllObjects(implicitModel);  
21.    }  
22.    else if (returnValue == null) {  
23.        // Either returned null or was 'void' return.  
24.        if (this.responseArgumentUsed || webRequest.isNotModified()) {  
25.            return null;  
26.        }  
27.        else {  
28.            // Assuming view name translation...  
29.            return new ModelAndView().addAllObjects(implicitModel);  
30.        }  
31.    }  
32.    else if (!BeanUtils.isSimpleProperty(returnValue.getClass())) {  
33.        // Assume a single model attribute...  
34.        ModelAttribute attr = AnnotationUtils.findAnnotation(handlerMethod, ModelAttribute.class);  
35.        String attrName = (attr != null ? attr.value() : "");  
36.        ModelAndView mav = new ModelAndView().addAllObjects(implicitModel);  
37.        if ("".equals(attrName)) {  
38.            Class resolvedType = GenericTypeResolver.resolveReturnType(handlerMethod, handlerType);  
39.            attrName = Conventions.getVariableNameForReturnType(handlerMethod, resolvedType, returnValue);  
40.        }  
41.        return mav.addObject(attrName, returnValue);  
42.    }  
43.    else {  
44.        throw new IllegalArgumentException("Invalid handler method return value: " + returnValue);  
45.    }  
46.}  
@SuppressWarnings("unchecked")
public ModelAndView getModelAndView(Method handlerMethod, Class handlerType, Object returnValue,
ExtendedModelMap implicitModel, ServletWebRequest webRequest) {

if (returnValue instanceof ModelAndView) {
ModelAndView mav = (ModelAndView) returnValue;
mav.getModelMap().mergeAttributes(implicitModel);
return mav;
}
else if (returnValue instanceof Model) {
return new ModelAndView().addAllObjects(implicitModel).addAllObjects(((Model) returnValue).asMap());
}
else if (returnValue instanceof Map) {
return new ModelAndView().addAllObjects(implicitModel).addAllObjects((Map) returnValue);
}
else if (returnValue instanceof View) {
return new ModelAndView((View) returnValue).addAllObjects(implicitModel);
}
else if (returnValue instanceof String) {
return new ModelAndView((String) returnValue).addAllObjects(implicitModel);
}
else if (returnValue == null) {
// Either returned null or was 'void' return.
if (this.responseArgumentUsed || webRequest.isNotModified()) {
return null;
}
else {
// Assuming view name translation...
return new ModelAndView().addAllObjects(implicitModel);
}
}
else if (!BeanUtils.isSimpleProperty(returnValue.getClass())) {
// Assume a single model attribute...
ModelAttribute attr = AnnotationUtils.findAnnotation(handlerMethod, ModelAttribute.class);
String attrName = (attr != null ? attr.value() : "");
ModelAndView mav = new ModelAndView().addAllObjects(implicitModel);
if ("".equals(attrName)) {
Class resolvedType = GenericTypeResolver.resolveReturnType(handlerMethod, handlerType);
attrName = Conventions.getVariableNameForReturnType(handlerMethod, resolvedType, returnValue);
}
return mav.addObject(attrName, returnValue);
}
else {
throw new IllegalArgumentException("Invalid handler method return value: " + returnValue);
}
}
}

返回值的定义十分庞大，或者说可怕的if-else多少有点让我觉得厌恶！
我们可以定义以下类型的返回值：

引用

ModelAndView
Model
View
Map
String
null


ModelAndView、Model和View都是Spring之前版本所特有的元素，Map对应于传入参数ModelMap，String定义页面名称，null即对应void类型方法！
最常用的实现方式如下：

Java代码 
1.@SuppressWarnings("unchecked")  
2.@RequestMapping(method = RequestMethod.GET)   
3.public String hello(String username, String password, ModelMap model) {   
4. 
5.    System.out.println(accountService.verify(username, password));  
6. 
7.    model.put("msg", username);   
8. 
9.    return "account";   
10.} 
Java代码
1.@SuppressWarnings("unchecked")  
2.@RequestMapping(method = RequestMethod.GET)  
3.public String hello(String username, String password, ModelMap model) {  
4. 
5.    System.out.println(accountService.verify(username, password));  
6. 
7.    model.put("msg", username);  
8. 
9.    return "account";  
10.} 
@SuppressWarnings("unchecked")
@RequestMapping(method = RequestMethod.GET)
public String hello(String username, String password, ModelMap model) {

System.out.println(accountService.verify(username, password));

model.put("msg", username);

return "account";
}

当然，对于我来说在返回值中写入这么一个字符串多少有点不能接受，于是我还是乐于使用输入参数ModelMap+输出参数Map的方式。
给出一个完整的AccountController实现：
AccountController.java

Java代码 
1./** 
2. * 2010-1-23 
3. */ 
4.package org.zlex.spring.controller;   
5. 
6.import java.util.Map;   
7. 
8.import org.springframework.beans.factory.annotation.Autowired;   
9.import org.springframework.stereotype.Controller;   
10.import org.springframework.ui.ModelMap;   
11.import org.springframework.web.bind.annotation.RequestMapping;   
12.import org.springframework.web.bind.annotation.RequestMethod;   
13.import org.zlex.spring.service.AccountService;   
14. 
15./** 
16. *  
17. * @author <a href="mailto:[e-mail]">梁栋</a> 
18. * @version 1.0 
19. * @since 1.0 
20. */ 
21.@Controller  
22.@RequestMapping("/account.do")   
23.public class AccountController {   
24. 
25.    @Autowired  
26.    private AccountService accountService;   
27. 
28.    @SuppressWarnings("unchecked")   
29.    @RequestMapping(method = RequestMethod.GET)   
30.    public Map hello(String username, String password, ModelMap model) {   
31. 
32.        System.out.println(accountService.verify(username, password));  
33. 
34.        model.put("msg", username);   
35.        return model;   
36.    }  
37.} 
Java代码
1./** 
2. * 2010-1-23 
3. */ 
4.package org.zlex.spring.controller;  
5. 
6.import java.util.Map;  
7. 
8.import org.springframework.beans.factory.annotation.Autowired;  
9.import org.springframework.stereotype.Controller;  
10.import org.springframework.ui.ModelMap;  
11.import org.springframework.web.bind.annotation.RequestMapping;  
12.import org.springframework.web.bind.annotation.RequestMethod;  
13.import org.zlex.spring.service.AccountService;  
14. 
15./** 
16. *  
17. * @author <a href="mailto:[e-mail]">梁栋</a> 
18. * @version 1.0 
19. * @since 1.0 
20. */ 
21.@Controller 
22.@RequestMapping("/account.do")  
23.public class AccountController {  
24. 
25.    @Autowired 
26.    private AccountService accountService;  
27. 
28.    @SuppressWarnings("unchecked")  
29.    @RequestMapping(method = RequestMethod.GET)  
30.    public Map hello(String username, String password, ModelMap model) {  
31. 
32.        System.out.println(accountService.verify(username, password));  
33. 
34.        model.put("msg", username);  
35.        return model;  
36.    }  
37.} 
/**
* 2010-1-23
*/
package org.zlex.spring.controller;

import java.util.Map;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.zlex.spring.service.AccountService;

/**
*
* @author <a href="mailto:[e-mail]">梁栋</a>
* @version 1.0
* @since 1.0
*/
@Controller
@RequestMapping("/account.do")
public class AccountController {

@Autowired
private AccountService accountService;

@SuppressWarnings("unchecked")
@RequestMapping(method = RequestMethod.GET)
public Map hello(String username, String password, ModelMap model) {

System.out.println(accountService.verify(username, password));

model.put("msg", username);
return model;
}
}

最后说注解@Session
如果想将某个ModelMap中的参数指定到Session中，可以使用@Session注解，将其绑定为Session熟悉，代码如下所示：

Java代码 
1.@Controller 
2.@RequestMapping("/account.do")   
3.@SessionAttributes("msg")   
4.public class AccountController {   
5. 
6.    @Autowired  
7.    private AccountService accountService;   
8. 
9.    @SuppressWarnings("unchecked")   
10.    @RequestMapping(method = RequestMethod.GET)   
11.    public Map hello(String username, String password, ModelMap model) {   
12. 
13.        System.out.println(accountService.verify(username, password));  
14. 
15.        model.put("msg", username);   
16.        return model;   
17.    }  
18. 
19.} 
Java代码
1.@Controller 
2.@RequestMapping("/account.do")  
3.@SessionAttributes("msg")  
4.public class AccountController {  
5. 
6.    @Autowired 
7.    private AccountService accountService;  
8. 
9.    @SuppressWarnings("unchecked")  
10.    @RequestMapping(method = RequestMethod.GET)  
11.    public Map hello(String username, String password, ModelMap model) {  
12. 
13.        System.out.println(accountService.verify(username, password));  
14. 
15.        model.put("msg", username);  
16.        return model;  
17.    }  
18. 
19.} 
@Controller
@RequestMapping("/account.do")
@SessionAttributes("msg")
public class AccountController {

@Autowired
private AccountService accountService;

@SuppressWarnings("unchecked")
@RequestMapping(method = RequestMethod.GET)
public Map hello(String username, String password, ModelMap model) {

System.out.println(accountService.verify(username, password));

model.put("msg", username);
return model;
}

}

当然，我们还需要配置一下对应的视图解析器，给出完整配置：
servelt.xml

Xml代码 
1.<?xml version="1.0" encoding="UTF-8"?> 
2.<beans  
3.    xmlns="http://www.springframework.org/schema/beans"  
4.    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
5.    xmlns:p="http://www.springframework.org/schema/p"  
6.    xmlns:context="http://www.springframework.org/schema/context"  
7.    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd   
8.        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">  
9.    <context:component-scan  
10.        base-package="org.zlex.spring.controller" />  
11.    <bean  
12.        id="urlMapping"  
13.        class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" />  
14.    <bean  
15.        class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />  
16.    <bean  
17.        id="jstlViewResolver"  
18.        class="org.springframework.web.servlet.view.InternalResourceViewResolver"  
19.        p:viewClass="org.springframework.web.servlet.view.JstlView"  
20.        p:prefix="/WEB-INF/page/"  
21.        p:suffix=".jsp" />  
22.</beans>  
Xml代码
1.<?xml version="1.0" encoding="UTF-8"?> 
2.<beans 
3.    xmlns="http://www.springframework.org/schema/beans" 
4.    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
5.    xmlns:p="http://www.springframework.org/schema/p" 
6.    xmlns:context="http://www.springframework.org/schema/context" 
7.    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd  
8.        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> 
9.    <context:component-scan 
10.        base-package="org.zlex.spring.controller" /> 
11.    <bean 
12.        id="urlMapping" 
13.        class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" /> 
14.    <bean 
15.        class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" /> 
16.    <bean 
17.        id="jstlViewResolver" 
18.        class="org.springframework.web.servlet.view.InternalResourceViewResolver" 
19.        p:viewClass="org.springframework.web.servlet.view.JstlView" 
20.        p:prefix="/WEB-INF/page/" 
21.        p:suffix=".jsp" /> 
22.</beans> 
<?xml version="1.0" encoding="UTF-8"?>
<beans
xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan
base-package="org.zlex.spring.controller" />
<bean
id="urlMapping"
class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" />
<bean
class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />
<bean
id="jstlViewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver"
p:viewClass="org.springframework.web.servlet.view.JstlView"
p:prefix="/WEB-INF/page/"
p:suffix=".jsp" />
</beans>

这里使用了JstlView作为视图解析器。同时，指定前缀路径为"/WEB-INF/page/"，后缀路径为".jsp"。也就是说，Spring容器将会在这个路径中寻找匹配的jsp文件！
注意加入xmlns:p="http://www.springframework.org/schema/p"命名空间！
再给出页面内容：
taglib.jsp

Jsp代码 
1.<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>  
2.<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%>   
3.<%@ taglib prefix="sql" uri="http://java.sun.com/jsp/jstl/sql"%>   
4.<%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml"%>   
5.<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%>   
6.<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>   
7.<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>  
Jsp代码
1.<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>  
2.<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%>  
3.<%@ taglib prefix="sql" uri="http://java.sun.com/jsp/jstl/sql"%>  
4.<%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml"%>  
5.<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%>  
6.<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>  
7.<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%> 
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%>
<%@ taglib prefix="sql" uri="http://java.sun.com/jsp/jstl/sql"%>
<%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml"%>
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%>
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>

account.jap

Jsp代码 
1.<%@ page language="java" contentType="text/html; charset=UTF-8" 
2.    pageEncoding="UTF-8"%>   
3.<%@ include file="/WEB-INF/page/taglib.jsp"%>   
4.<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">   
5.<html>  
6.<head>  
7.<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">   
8.<title>Account</title>  
9.</head>  
10.<body>  
11.<c:out value="${msg}"></c:out>   
12.</body>  
13.</html> 
Jsp代码
1.<%@ page language="java" contentType="text/html; charset=UTF-8" 
2.    pageEncoding="UTF-8"%>  
3.<%@ include file="/WEB-INF/page/taglib.jsp"%>  
4.<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">  
5.<html>  
6.<head>  
7.<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">  
8.<title>Account</title>  
9.</head>  
10.<body>  
11.<c:out value="${msg}"></c:out>  
12.</body>  
13.</html> 
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ include file="/WEB-INF/page/taglib.jsp"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Account</title>
</head>
<body>
<c:out value="${msg}"></c:out>
</body>
</html>

目录结构如图所示：

启动应用，最后将得到一个带有内容的页面，如图：

代码见附件！