Spring MVC提供了以下几种途径输出模型数据：

1）ModelAndView：处理方法返回值类型为ModelAndView时，方法体即可通过该对象添加模型数据；

2）Map及Model：处理方法入参为org.springframework.ui.Model、org.springframework.ui.ModelMap或java.util.Map时，处理方法返回时，Map中的数据会自动被添加到模型中；

3）@SessionAttributes：将模型中的某个属性暂存到HttpSeession中，以便多个请求之间可以共享这个属性；

4）@ModelAttribute：方法入参标注该注解后，入参的对象就会放到数据模型中。

在SpringMVC的hanlder类中用@ModelAttribute标注的方法，会在该handler内所有目标（action）方法执行之前被SpringMVC调用。

用法示例：

Account.java

1 package com.dx.springlearn.entities; 2  3 public class Account { 4     public Integer id; 5     private String username; 6     private String password; 7     private String registerDate; 8     private String registerIP; 9 10     public Account() {11     }12 13     public Account(Integer id, String username, String password, String registerDate, String registerIP) {14         super();15         this.id = id;16         this.username = username;17         this.password = password;18         this.registerDate = registerDate;19         this.registerIP = registerIP;20     }21 22     public Account(String username, String password, String registerDate, String registerIP) {23         super();24         this.username = username;25         this.password = password;26         this.registerDate = registerDate;27         this.registerIP = registerIP;28     }29 30     public Integer getId() {31         return id;32     }33 34     public void setId(Integer id) {35         this.id = id;36     }37 38     public String getUsername() {39         return username;40     }41 42     public void setUsername(String username) {43         this.username = username;44     }45 46     public String getPassword() {47         return password;48     }49 50     public void setPassword(String password) {51         this.password = password;52     }53 54     public String getRegisterDate() {55         return registerDate;56     }57 58     public void setRegisterDate(String registerDate) {59         this.registerDate = registerDate;60     }61 62     public String getRegisterIP() {63         return registerIP;64     }65 66     public void setRegisterIP(String registerIP) {67         this.registerIP = registerIP;68     }69 70     @Override71     public String toString() {72         return "Account [id=" + id + ", username=" + username + ", password=" + password + ", registerDate="73                 + registerDate + ", registerIP=" + registerIP + "]";74     }75 76     77 }

Handler类TestModelData.java

1 package com.dx.springlearn.hanlders; 2  3 import java.text.SimpleDateFormat; 4 import java.util.Date; 5 import java.util.Map; 6  7 import org.springframework.stereotype.Controller; 8 import org.springframework.web.bind.annotation.ModelAttribute; 9 import org.springframework.web.bind.annotation.RequestMapping;10 import org.springframework.web.bind.annotation.RequestParam;11 import org.springframework.web.servlet.ModelAndView;12 13 import com.dx.springlearn.entities.Account;14 15 @Controller16 public class TestModelData {17     private final String SUCCESS = "success";18 19     @ModelAttribute20     public void getAccount(@RequestParam(name = "id", required = false) Integer id, Map
     
       map) {21         if (id != null) {22             System.out.println("read account(id=" + id + ") from db");23             Account account = new Account(1, "tommy", "123456", "2018-01-20 21:56:09", "127.0.0.1");24             map.put("account", account);25         } else {26             System.out.println("the acount id is null");27         }28     }29 30     @RequestMapping("/testModelAttribute")31     public ModelAndView testModelAttribute(Account account) {32         System.out.println("accept account:" + account);33         String viewName = SUCCESS;34         ModelAndView modelAndView = new ModelAndView(viewName);35         modelAndView.addObject("currentTime", new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()));36 37         return modelAndView;38     }39 }
     

测试表单页面：

     
        
              username:
      
      
        
              register date:
      
      
        register ip:
      
      
        
          
     

除了handler目标方法参数第一个参数名称与存放到map中的对象名称一致外，也可以使用@ModelAttribute标注handler目标方法参数：

package com.dx.springlearn.hanlders;import java.text.SimpleDateFormat;import java.util.Date;import java.util.Map;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.ModelAttribute;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestParam;import org.springframework.web.servlet.ModelAndView;import com.dx.springlearn.entities.Account;@Controllerpublic class TestModelData {    private final String SUCCESS = "success";    @ModelAttribute    public void getAccount(@RequestParam(name = "id", required = false) Integer id, Map
     
       map) {        if (id != null) {            System.out.println("read account(id=" + id + ") from db");            Account account = new Account(1, "tommy", "123456", "2018-01-20 21:56:09", "127.0.0.1");            map.put("testabc", account);        } else {            System.out.println("the acount id is null");        }    }    @RequestMapping("/testModelAttribute")    public ModelAndView testModelAttribute(@ModelAttribute("testabc") Account account) {        System.out.println("accept account:" + account);        String viewName = SUCCESS;        ModelAndView modelAndView = new ModelAndView(viewName);        modelAndView.addObject("currentTime", new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()));        return modelAndView;    }}
     

运行流程：

1）运行有@ModelAttribute注解标注的方法：从数据库中取出对象，把对象放入到Map中，键值为：user；

2）SpringMVC从Map中取出User对象，并把表单的请求参数赋值给该User对象的对应属性；

3）SpringMVC把上述对象传入目标方法的参数（参数名称必须与Map中的键值一致）。

注意：在@ModelAttribute修饰的方法中，放入Map是的键类型要与目标方法入参类型一直，而且Map是的键名称要与目标方法入参的参数名一致。