springMVC入门（四）------参数绑定与返回值类型

2022-09-26 15:01:52

简介

从之前的介绍，已经可以使用springMVC完成完整的请求、返回数据的功能。

待解决的问题：如何将数据传入springMVC的控制器进行后续的处理，完成在原生servlet/jsp开发中HttpServletRequet的功能。

解决方案：springMVC参数绑定，即将客户端请求的数据绑定到处理器方法的形参上(也有特例，如Model、ModelMap、HttpServletResponse是返回)

默认的参数绑定

springMVC默认支持一下类型的参数绑定：

HttpServletRequest

HttpServletResponse

HttpSession

Model/ModelMap(本质一样，Model是接口、ModelMap是实现)

//此注解使得注解扫描器将此Controller加载进spring IOC容器进行管理

@Controller

public class UserController {

    //此注解建立URL与此处理方法的映射关系

    @RequestMapping("/queryUser")

    public String queryUser(HttpServletRequest request, HttpServletResponse response

            , HttpSession session, ModelMap model) {

        String username = request.getParameter("username");

        String email = request.getParameter("email");

        //模拟后台数据

        User user = new User();

        user.setUsername(username);

        user.setEmail(email);

        //返回数据与视图

        model.put("user", user);

        return "/WEB-INF/jsp/user.jsp";

    }

}

结果：

至此也引出了Controller方法返回值并不一定要是ModelAndView

Controller方法的返回值类型可为：

1、ModelAndView

2、String(可通过HttpServletRequest、Model/ModelMap返回数据)

3、void(可通过HttpServletResponse返回json数据)

简单数据类型的参数绑定

简单数据类型参数绑定成功的前提：jsp标签name属性名，与Controller方法的形参名一致

//此注解使得注解扫描器将此Controller加载进spring IOC容器进行管理

@Controller

public class UserController {

    //此注解建立URL与此处理方法的映射关系

    @RequestMapping("/queryUser")

    public String queryUser(int id, String username, Model model) {

        //模拟后台数据

        User user = new User();

        user.setUsername(username);

        //返回数据与视图

        model.addAttribute("user", user);

        model.addAttribute("id", id);

        return "/WEB-INF/jsp/user.jsp";

    }

}

jsp页面增加id输出

<h2>Hello World!</h2>

${user.username}<br/>

${user.email}

${id}

结果：

POJO参数绑定

POJO数据类型参数绑定成功的前提：客户端请求的key/value数据，key的值与POJO字段名一致

//此注解使得注解扫描器将此Controller加载进spring IOC容器进行管理

@Controller

public class UserController {

    //此注解建立URL与此处理方法的映射关系

    @RequestMapping("/queryUser")

    public ModelAndView queryUser(User user) {

        //模拟后台数据

        //返回数据与视图

        return new ModelAndView("/WEB-INF/jsp/user.jsp").addObject("user", user);

    }

}

结果：

包装POJO的参数绑定

包装POJO数据类型参数绑定前提：jsp标签name属性名要按照javabean的层级结构命名

    @RequestMapping("/addAuthority")

    public ModelAndView addAuthority(User user) {

        //模拟后台数据

        //返回数据与视图

        user.getAuthority().setId(user.getAuthority().getId() + 10);

        user.getAuthority().setDescription(user.getAuthority().getDescription() + "abcd");

        return new ModelAndView("/index.jsp").addObject("user", user);

    }
public class User {

    private String username;

    private String email;

    private UserAuthority authority;

    public String getUsername() {

        return username;

    }

    public void setUsername(String username) {

        this.username = username;

    }

    public String getEmail() {

        return email;

    }

    public void setEmail(String email) {

        this.email = email;

    }

    public UserAuthority getAuthority() {

        return authority;

    }

    public void setAuthority(UserAuthority authority) {

        this.authority = authority;

    }

}
public class UserAuthority {

    private String id;

    private String description;

    public String getId() {

        return id;

    }

    public void setId(String id) {

        this.id = id;

    }

    public String getDescription() {

        return description;

    }

    public void setDescription(String description) {

        this.description = description;

    }

}

JSP页面

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<%@ page language="java" contentType="text/html; charset=utf-8"  pageEncoding="utf-8" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<body>

<h2>Hello World!</h2>

</body>

<form action="${request.getServletContext().getServletPath()}/springMVC/addAuthority.action" method="post">

    <!-- 注意name名称 -->

    权限编码：<input name="authority.id" type="text" value="${user.authority.id}"/><br/>

    权限描述：<input name="authority.description" type="text" value="${user.authority.description}"/><br/>

    <input type="submit" value = "提交"/>

</form>

</ht>

结果：

数组的参数绑定

数据参数绑定成功前提：jsp标签name属性值与Controller形参名一致

 @RequestMapping("/addArray")

    public ModelAndView addArray(String[] names) {

        //模拟后台数据

        //返回数据与视图

        if(null != names) {

            for(int i = 0 ; i < names.length ; i++) {

                names[i] = names[i] + " 2B";

            }

        }

        return new ModelAndView("/index.jsp").addObject("names", names);

    }

JSP页面

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<%@ page language="java" contentType="text/html; charset=utf-8"  pageEncoding="utf-8" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<body>

<h2>Hello World!</h2>

</body>

<form action="${request.getServletContext().getServletPath()}/springMVC/addArray.action" method="post">

    <input type="text" name="names" /><br/>

    <input type="text" name="names" />

    <input type="submit" value="提 交"/>

</form>

用户：

<c:forEach items="${names}" var="name">

    ${name}<br/>

</c:forEach>

</html>

结果：

List类型的参数绑定

List类型绑定成功的前提：必须通过POJO包装类接收List类型

 @RequestMapping("/addUser")

    public ModelAndView addUser(User user) {

        System.out.println(JsonUtils.objectToJsonString(user));

        return new ModelAndView("/index.jsp");

    }
public class User {

    private String username;

    private String email;

    private List<UserAuthority> authorities;

    public String getUsername() {

        return username;

    }

    public void setUsername(String username) {

        this.username = username;

    }

    public String getEmail() {

        return email;

    }

    public void setEmail(String email) {

        this.email = email;

    }

    public List<UserAuthority> getAuthorities() {

        return authorities;

    }

    public void setAuthorities(List<UserAuthority> authorities) {

        this.authorities = authorities;

    }

}

JSP页面：

<html>

<body>

<h2>Hello World!</h2>

</body>

<form action="${request.getServletContext().getServletPath()}/springMVC/addUser.action" method="post">

    <table frame="border">

        <tr>

            <th>用户名</th>

            <td><input type="text" name="username"/></td>

            <th>email</th>

            <td><input type="text" name="email"/></td>

        </tr>

        <tr>

            <td colspan="2">权限编码</td>

            <td colspan="2">权限描述</td>

        </tr>

        <tr>

            <td colspan="2"><input type="text" name="authorities[0].id"/></td>

            <td colspan="2"><input type="text" name="authorities[0].description"/></td>

        </tr>

        <tr>

            <td colspan="2"><input type="text" name="authorities[1].id"/></td>

            <td colspan="2"><input type="text" name="authorities[1].description"/></td>

        </tr>

    </table>

    <input type="submit" value = "提交"/>

</form>

</html>

结果：

Map类型的参数绑定

Map类型绑定成功的前提：必须通过POJO包装类接收Map类型

@RequestMapping("/addUser")

    public ModelAndView addUser(User user) {

        System.out.println(JsonUtils.objectToJsonString(user));

        return new ModelAndView("/index.jsp");

    }
public class User {

    private String username;

    private String email;

    private Map<String, String> authorities;

    public String getUsername() {

        return username;

    }

    public void setUsername(String username) {

        this.username = username;

    }

    public String getEmail() {

        return email;

    }

    public void setEmail(String email) {

        this.email = email;

    }

    public Map<String, String> getAuthorities() {

        return authorities;

    }

    public void setAuthorities(Map<String, String> authorities) {

        this.authorities = authorities;

    }

}

结果：

JSP页面

<html>

<body>

<h2>Hello World!</h2>

</body>

<form action="${request.getServletContext().getServletPath()}/springMVC/addUser.action" method="post">

    <table frame="border">

        <tr>

            <th>用户名</th>

            <td><input type="text" name="username"/></td>

            <th>email</th>

            <td><input type="text" name="email"/></td>

        </tr>

        <tr>

            <td>权限编码</td>

            <td><input type="text" name="authorities[id]"/></td>

            <td>权限描述</td>

            <td><input type="text" name="authorities[description]"/></td>

        </tr>

    </table>

    <input type="submit" value = "提交"/>

</form>

</html>

其它知识点

1、springMVC使用Converter(老版本中使用PropertyEditor)进行请求数据到参数绑定数据之间的类型转换

springmvc提供了很多Converter，特殊情况下需要使用自定义Converter(比如对日期数据的绑定)

此时需自定义转换类，并实现Convert<S,T>接口，并在配置文件中进行注册

2、有时界面标签name值与形参字段名不一致时，可以通过@RequestParam注解建立映射关系

通过required属性可指定参数是否必须传入

通过defaultValue属性可指定默认值

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