0056 Spring MVC如何接收浏览器传递来的请求参数--request--形参--实体类封装

浏览器总会向服务器传递一些参数，那么Spring MVC如何接收这些参数？

先写个简单的html，向服务器传递一些书籍信息，如下：

<!DOCTYPE html>

<html>

<head>

    <title>Spring MVC如何接受浏览器传递来的参数</title>

    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

</head>

<body>

    <form action="addbook" method="POST">

        <fieldset>

            <legend>要上传的书籍信息</legend>

             书名：<input name="bookname" /><br>

            作者：<input name="author" /><br>

            出版社：<input name="press" /><br>

            ISBN：<input name="isbn" /><br>

            豆瓣评分：<input name="douban" /><br>

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

        </fieldset>

    </form>

</body>

</html>

再写个视图result.jsp

<%@page pageEncoding="utf-8"

        contentType="text/html;charset=utf-8" %>

<html>

    <head>

        <title>返回结果</title>

    </head>

    <body style="color:blue;font-size:18px">

        您输入的书籍信息为：<br>

        书籍的名称：${bookname }<br><br>

        书籍的作者：${author }<br><br>

        书籍的出版社：${press }<br><br>

        书籍的ISBN：${isbn }<br><br>

        书籍的豆瓣评分：${douban }<br><br>

    </body>

</html>

1. 通过HttpServletRequest获得请求参数和数据

tomcat类容器会自动将请求的参数封装到HttpServletRequest中

package net.sonng.mvcdemo.controller;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.servlet.ModelAndView;

@Controller

public class BookController {

    @RequestMapping(value="/addbook",method=RequestMethod.POST)

    public ModelAndView addbook(HttpServletRequest request,HttpServletResponse response) throws Exception{

        request.setCharacterEncoding("utf-8");    //将请求的编码设为utf-8

        String bookname=request.getParameter("bookname");  //从request中或参数值

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

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

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

        float douban=Float.parseFloat(request.getParameter("douban"));

        ModelAndView mav=new ModelAndView();

        mav.addObject("bookname",bookname);

        mav.addObject("author",author);

        mav.addObject("press",press);

        mav.addObject("isbn",isbn);

        mav.addObject("douban", douban);

        mav.setViewName("result");

        return mav;

    }

}

2. 处理方法形参名==请求参数名

将处理方法的形参名设为跟传递来的参数名称相同，Spring会自动将参数值传递进来

package net.sonng.mvcdemo.controller;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.servlet.ModelAndView;

@Controller

public class BookController {

    @RequestMapping(value="/addbook",method=RequestMethod.POST)

    public ModelAndView addBook(String bookname,String author,String press,String isbn,float douban){

                                //将形参名跟请求参数名设为相同，自动将值传递进来

        ModelAndView mav=new ModelAndView();

        mav.addObject("bookname",bookname);

        mav.addObject("author",author);

        mav.addObject("press",press);

        mav.addObject("isbn",isbn);

        mav.addObject("douban", douban);

        mav.setViewName("result");

        return mav;

    }

}

用这种方式可能导致编码错误，这里没有request参数，那就在web.xml中添加个过滤器

    <filter>

        <filter-name>utf8Filter</filter-name>

        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>

        <init-param>

            <param-name>encoding</param-name>

            <param-value>UTF-8</param-value>

        </init-param>

    </filter>

    <filter-mapping>

        <filter-name>utf8Filter</filter-name>

       <servlet-name>springmvc</servlet-name>

    </filter-mapping>

3. 如果形参名跟请求参数名不一样怎么办呢？用@RequestParam注解

处理方法该成这样：

package net.sonng.mvcdemo.controller;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import net.sonng.mvcdemo.entity.Book;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.bind.annotation.RequestParam;

import org.springframework.web.servlet.ModelAndView;

@Controller

public class BookController {

    @RequestMapping(value="/addbook",method=RequestMethod.POST)

    public ModelAndView addBook(

            @RequestParam(name="bookname",required=true) String b,

            @RequestParam(value="author") String a,

            @RequestParam("press") String p,

            @RequestParam("isbn") String i,

            @RequestParam(value="douban",defaultValue="0.0") float d){

            //用@RequestParam注解将请求参数值赋值给形参

        ModelAndView mav=new ModelAndView();

        mav.addObject("bookname",b);

        mav.addObject("author",a);

        mav.addObject("press",p);

        mav.addObject("isbn",i);

        mav.addObject("douban", d);

        mav.setViewName("result");

        return mav;

    }

}

@RequestParam可以将指定的请求参数赋值给形参，该注解有4个参数

----name：指定请求参数名

----value：跟name属性相同

----required：boolean类型，该参数是否必须绑定。注意这是指是否必须有这个参数，而不是参数的值是否为null。如果该属性设置为true，但是又没有对应的参数传递来，那么会抛出异常：Required String parameter '参数名' is not present

----defaultValue：如果没有该参数，那么使用使用默认值

4. 用实体类接收

写个实体类，其实例变量名称跟传递来的参数名称相同，并将该实体类作为处理方法的形参，Spring会自动将请求参数封装到该实体类对象中

先写个Book实体类，注意实例变量名跟传递的参数名相同

package net.sonng.mvcdemo.entity;

public class Book {

    private String bookname; //实体类的形参名跟请求参数名相同

    private String press;

    private String author;

    private String isbn;

    private float douban;

    //省略getter、setter、toString

}

处理方法写成这样：

package net.sonng.mvcdemo.controller;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import net.sonng.mvcdemo.entity.Book;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.servlet.ModelAndView;

@Controller

public class BookController {

    @RequestMapping(value="/addbook",method=RequestMethod.POST)

                                //用实体类封装请求参数

    public ModelAndView addBook(Book book){

        ModelAndView mav=new ModelAndView();

        mav.addObject("book", book);

        mav.setViewName("result");

        return mav;

    }

}

result.jsp改一改

<%@page pageEncoding="utf-8"

        contentType="text/html;charset=utf-8" %>

<html>

    <head>

        <title>返回结果</title>

    </head>

    <body style="color:blue;font-size:18px">

        您输入的书籍信息为：<br>

        书籍的名称：${book.bookname }<br><br>  <!-- 从名为book的模型中拿到bookname数据 -->

        书籍的作者：${book.author }<br><br>

        书籍的出版社：${book.press }<br><br>

        书籍的ISBN：${book.isbn }<br><br>

        书籍的豆瓣评分：${book.douban }<br><br>

    </body>

</html>

最后，如何选择？

如果参数比较少，就用：形参名跟请求参数名相同的办法

如果参数比较多，就用：实体类封装

如果浏览器端没有做参数检查，那就从request拿值