Day28 Spring MVC - Request Handling (II) - iT 邦幫忙::一起幫忙解決難題，拯救 IT 人的一天

2024 iThome 鐵人賽

DAY 29

Software Development

從Servlet到Spring MVC系列第 29 篇

Day28 Spring MVC - Request Handling (II)

16th鐵人賽

James

2024-10-13 10:26:03

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0.創建module

請參考Day27 module

一、Request Handling

(1) @RequestParam

Spring MVC封裝了Servlet request parameter，可以處理query string的請求參數，也可以處理post傳來的form data

@Controller
public class RequestParamController {

    @GetMapping("RequestParamDemo")
    public String RequestParamPage(){
        return "RequestParamDemo";
    }

    @PostMapping("RequestParamDemoPost")
    @ResponseBody
    public String RequestParamDemoPost(@RequestParam Map<String, String> params){
        System.out.println("====RequestParamDemoPost====");
        for (String key : params.keySet()) {
            System.out.println(key + ":" + params.get(key));
        }
        System.out.println("====RequestParamDemoPost====");
        return "get POST data";
    }
    @GetMapping("RequestParamDemoGet")
    @ResponseBody
    public String RequestParamDemoGet(@RequestParam("account") String account,@RequestParam("password`") String password){
        System.out.println("====RequestParamDemoGet====");
        System.out.println("account:" + account);
        System.out.println("password:" + password);
        System.out.println("====RequestParamDemoGet====");
        return "get GET data";
    }
}

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>RequestParamDemo</title>
</head>
<body>
    <h3>POST method</h3>
    <form action="RequestParamDemoPost" method="post">
        帳號:<input name="account" type="text"><br>
        密碼:<input name="password" type="password"><br>
        <input type="submit" value="submit">
    </form>
    <br>
    <h3>GET method</h3>
    <form action="RequestParamDemoGet" method="get">
        帳號:<input name="account" type="text"><br>
        密碼:<input name="password" type="password"><br>
        <input type="submit" value="submit">
    </form>
</body>
</html>

Demo

先訪問RequestParamDemo，再依次執行POST與GET
case1

case2

(2) @PathVariable

在RESTful的web應用中會透過URL請求路徑的內容當作參數取出來應用，Spring MVC 提供@PathVariable讓我們可以方便從URL中取出對應的參數。

@Controller
public class PathVariableController {
    @GetMapping(path = "/emp/{id}/{name}")
    @ResponseBody
    public String pathVariableDemo(@PathVariable("id") int id, @PathVariable("name") String name){
        return "pathVariableDemo:id"+id+":name"+name;
    }
}

Demo

(3) @RequestBody

在前後端分離的專案中，最重要的莫過於JSON的處理。Spring MVC透過@RequestBody幫我們處理JSON直接轉成物件方便後續操作。支援JSON需要在Spring設定檔中設定處理JSON，否則會收到HTTP Status 415 – Unsupported Media Type的訊息。官網設定請點我

配置處理JSON

maven pom 引入相關JSON套件

 <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.17.1</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.module/jackson-module-parameter-names -->
    <dependency>
      <groupId>com.fasterxml.jackson.module</groupId>
      <artifactId>jackson-module-parameter-names</artifactId>
      <version>2.17.1</version>
    </dependency>

spring設定檔配置

<mvc:annotation-driven>
    <mvc:message-converters>
        <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
            <property name="objectMapper" ref="objectMapper"/>
        </bean>
    </mvc:message-converters>
</mvc:annotation-driven>
<bean id="objectMapper" class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean"
      p:indentOutput="true"
      p:simpleDateFormat="yyyy-MM-dd"
      p:modulesToInstall="com.fasterxml.jackson.module.paramnames.ParameterNamesModule"/>

Demo

Employee

public class Employee {
    private String empId;
    private String empName;
    //getter setter toString略
}

JsonController

@Controller
public class JsonController {

    @PostMapping(path = "JsonDemo")
    @ResponseBody
    public String JsonDemo(@RequestBody Employee emp){
        System.out.println(emp);
        return "JsonDemo";
    }
}

這邊使用Postman進行後端API測試

二、Native Api Handling

Spring MVC提供Method Arguments，讓我們可以方便調用原生的Servlet API

@Controller
public class NativeController {
    
    @ResponseBody
    @RequestMapping("NativeApi")
    public String NativeApi(HttpServletRequest request, HttpServletResponse response){
        String method = request.getMethod();
        System.out.println(method);
        Cookie cookie = new Cookie("NativeApi", "haha");
        response.addCookie(cookie);

        return "DemoNativeApi";
    }
}

三、Shared Objec

在使用傳統的jsp、themleaf等server side render頁面的技術就必須透過shared object來幫助我們數據傳遞到頁面中

(1) Request Scope

Spring MVC提供了Model、ModelMap、ModelAndView的方式作為傳遞數據物件的封裝，看完下面範例就知道如何使用了


@Controller
public class SharedObjectController {
    @GetMapping("ModelDemo")
    public String RequestDemo(Model model){
        model.addAttribute("msg", "Hello World");

        return "RequestDemo";
    }
    @GetMapping("ModelMapDemo")
    public String RequestDemo(ModelMap map){
        map.put("msg", "ModelMapDemo");
        return "RequestDemo";
    }
    @GetMapping("ModelAndViewDemo")
    public ModelAndView RequestDemo(ModelAndView modelAndView){
        modelAndView.addObject("msg", "ModelAndViewDemo");
        modelAndView.setViewName("RequestDemo");
        return modelAndView;
    }
}

Demo

(2) Session Scope

可以透過傳入HttpSession來調用session物件，在頁面可以透過sessionScope來調用設置參數

@GetMapping("SessionDemo")
public String SessionDemo(HttpSession session){
    session.setAttribute("msg", "SessionDemo");
    return "SessionDemo";
}

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>SessionDemo</title>
</head>
<body>
    ${sessionScope.msg}
</body>
</html>

Demo

(3) Application Scope

Spring MVC初始化容器時已將ServletContext註冊到容器當中，可以直接注入調用，在頁面中可以透過applicationScope調用設置參數

@Autowired
private ServletContext servletContext;
@GetMapping("ServletContextDemo")
public String ServletContextDemo(){
    servletContext.setAttribute("msg", "ServletContextDemo");
    return "ServletContextDemo";
}

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>SessionDemo</title>
</head>
<body>
    ${applicationScope.msg}
</body>
</html>