SSM 学习第五天

发表于 2022-12-31 更新于 2023-02-24 分类于学习

SpringMVC

入门案例

导入 maven 依赖

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>
    <scope>provided</scope>
</dependency>

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.2.10.RELEASE</version>
</dependency>

创建 Spring 控制类

package com.ljguo.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
@RequestMapping("/user")
public class UserController {
    @RequestMapping("/save")
    @ResponseBody
    public String save(){
        System.out.println("user save ...");
        return "{'info': 'spring-mvc-user'}";
    }
}

@Controller 让其加载到 Spring 容器中
@RequestMapping 用于映射访问的 url 路径
@ResponseBody 用于将方法返回值写到响应体中

创建 SpringMVC 配置类

package com.ljguo.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

@ComponentScan("com.ljguo.controller")
@EnableWebMvc
public class SpringMvcConfig {
}

@ComponentScan

初始化 Servlet 容器, 加载 SpringMVC 环境, 设置 SpringMVC 技术处理的请求

public class ServletContainersInitConfig extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[]{SpringConfig.class};
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[]{SpringMvcConfig.class};
    }

    @Override
    protected String[] getServletMappings() {
        return new String[]{"/"};
    }

    // 乱码处理
    @Override
    protected Filter[] getServletFilters() {
        CharacterEncodingFilter filter = new CharacterEncodingFilter();
        filter.setEncoding("utf-8");
        return new Filter[]{filter};
    }
}

继承 AbstractAnnotationConfigDispatcherServletInitializer, 重写三个方法并配置
getServletFilters 方法用于解决中文乱码

各种参数的传递

普通参数

@RequestMapping("/save")
@ResponseBody
public String save(String username, String password){
    return username + ": " + password;
}

前端传输

1 2	username password

pojo 参数

@RequestMapping("/pojo")
@ResponseBody
public String pojoParam(User user) {
    return user.toString();
}

嵌套 pojo 参数

username
password
address.province
address.city

数组

@RequestMapping("/array")
@ResponseBody
public String arrayParam(String[] likes) {
    return Arrays.toString(likes);
}

前端传输

likes
likes
likes
...

集合

@RequestMapping("/list")
@ResponseBody
public String listParam(@RequestParam List<String> likes) {
    return likes.toString();
}

前端传输

likes
likes
likes
...

记得加上 @RequestParam 在参数上

Date 时间类型

@RequestMapping("/date")
@ResponseBody
public String dateParam(@DateTimeFormat(pattern = "yyyy-MM-dd") Date date) {
    return date.toString();
}

前端传输

1 2	2022/10/20 2022-10-20

注意默认时间格式是 yyyy/MM/dd, 如需其它格式, 需要使用 @DateTimeFormat 注解中的 pattern 指定格式

json
这里需要在 SpringMVC 的配置类中加入 @EnableWebMvc 注解, 用于开启由 json 数据转化为我们的对象的功能

@RequestMapping("/list")
@ResponseBody
public String listParam(@RequestBody List<User> users) {
    System.out.println(users);
    return likes.toString();
}

响应

页面跳转
1
2
3
4
@RequestMapping("/jumpPage")
public String jumpPage() {
return "/index.jsp";
}
注意不要加 @ResponseBody 注解, 因为这个注解是将返回值写入响应体中, 便无法做到页面跳转

纯文字

@RequestMapping("/toText")
@ResponseBody
public String toText() {
    return "hello world!";
}

json 数据

@RequestMapping("/toJson")
@ResponseBody
public User toJson() {
    User user = new User("ljguo","20001020",new Address("sichuan","nanchong"));
    return user;
}

@RequestMapping("/userList")
@ResponseBody
public List<User> userList() {
    User user = new User("ljguo","20001020",new Address("sichuan","nanchong"));
    User user1 = new User("ljguo1","20001020",new Address("sichuan","nanchong"));
    User user2 = new User("ljguo2","20001020",new Address("sichuan","nanchong"));
    List<User> userList = new ArrayList<>();
    userList.add(user);
    userList.add(user1);
    userList.add(user2);
    return userList;
}

这里的原理是 SpringMVC 依赖 @ResponseBody 注解并使用 Jackson 类帮我们实现了对象转化为 json 数据并传递到响应体

REST 风格

REST: Representational State Transfer 表现形式状态转换

传统风格

1 2	http://localhost/user/getById?id=1 http://localhost/user/addUser

REST

1 2	http://localhost/user/1 http://localhost/user

优点

隐藏访问行为, 无法通过地址来得知行为
书写简化

需要使用不同的请求方式

http://localhost/users      查全部信息(GET)
http://localhost/users/1    查指定信息(GET)
http://localhost/users      添加(POST)
http://localhost/users      修改(PUT)
http://localhost/users/1    删除(DELETE)

入门案例

@RequestMapping(value = "/{id}",method = RequestMethod.GET)
@ResponseBody
public String save(@PathVariable int id){
    System.out.println("user save ..." + id);
    return "{'info': 'spring-mvc-user'}";
}

value = "/{id}" 对应 @PathVariable int id 实现对路径参数的解析
method = RequestMethod.GET 设置请求方式

@RequestParam 用于接收表单数据
@RequestBody 用于接收 json 数据
@PathVariable 用于接收路径参数

简化

1 2	@Controller @ResponseBody

替换为

1	@RestController

1	@RequestMapping(value = "/{id}", method = RequestMethod.GET)

替换为

1	@GetMapping("/{id}")

SpringMVC 资源放行

配置一个资源放行类, 继承 WebMvcConfigurationSupport 类, 重写 addResourceHandlers() 方法

@Configuration
public class SpringSupport extends WebMvcConfigurationSupport {
    @Override
    protected void addResourceHandlers(ResourceHandlerRegistry registry) {
        // 放行, 即访问这些路径时, 不走 SpringMVC, 而是走 tomcat
        registry.addResourceHandler("/**").addResourceLocations("/");
    }
}