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
package com.dx.springlearn.entities;
public class Account {
public Integer id;
private String username;
private String password;
private String registerDate;
private String registerIP;
public Account() {
}
public Account(Integer id, String username, String password, String registerDate, String registerIP) {
super();
this.id = id;
this.username = username;
this.password = password;
this.registerDate = registerDate;
this.registerIP = registerIP;
}
public Account(String username, String password, String registerDate, String registerIP) {
super();
this.username = username;
this.password = password;
this.registerDate = registerDate;
this.registerIP = registerIP;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getRegisterDate() {
return registerDate;
}
public void setRegisterDate(String registerDate) {
this.registerDate = registerDate;
}
public String getRegisterIP() {
return registerIP;
}
public void setRegisterIP(String registerIP) {
this.registerIP = registerIP;
}
@Override
public String toString() {
return "Account [id=" + id + ", username=" + username + ", password=" + password + ", registerDate="
+ registerDate + ", registerIP=" + registerIP + "]";
}
}
Handler类TestModelData.java
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; @Controller
public class TestModelData {
private final String SUCCESS = "success"; @ModelAttribute
public void getAccount(@RequestParam(name = "id", required = false) Integer id, Map<String, Object> 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("account", account);
} else {
System.out.println("the acount id is null");
}
} @RequestMapping("/testModelAttribute")
public ModelAndView testModelAttribute(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;
}
}
测试表单页面：
<form id="form_testModelAttribute" action="testModelAttribute"
method="POST">
<input name="id" type="hidden" value="1"/>
username:<input name="username" type="text" value="tommy" /><br>
<!-- password:<input name="password" type="password" /><br> -->
register date:<input name="registerDate" type="text" value="2018-01-20 21:56:09" /><br>
register ip:<input name="registerIP" type="text" value="127.0.0.1"/><br>
<input type="submit" value="Submit"/>
</form>
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; @Controller
public class TestModelData {
private final String SUCCESS = "success"; @ModelAttribute
public void getAccount(@RequestParam(name = "id", required = false) Integer id, Map<String, Object> 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。