【Spring-boot框架】内嵌Tomcat，启动项目

spring boot真的好好用哦，在单位试了这个，不行，今天回来直接就好了，开心~

一、启动项目

第一步：pom.xml文件中加入以下依赖

 
     org.springframework.boot
     spring-boot-starter-web
 

第二步：创建一个启动类Start，使用@SpringBootApplication注解，运行main方法，即可启动spring boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class start {
    public static void main(String[] args){
        SpringApplication.run(start.class,args);
    }
}

启动一下

第三步：写一个接口，/start/springboot

@RestController注解返回json格式数据

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

@RestController
@RequestMapping("/start")
public class StartController {

    @RequestMapping("/springboot")
    public String startSpringBoot(){
        return "welcome to spring boot";
    }
    
}

第四步：在浏览器输入：localhost:8080/start/springboot

出现如下图及说明项目启动成功！

二、Spring Boot返回Json数据及数据封装

接口与接口间、前后端间传输用json

Spring Boot中，Controller 中使用@RestController注解即可返回 Json 格式的数据

常用的数据结构：类对象/List对象/Map对象

2.1、不同数据类型返回json数据

第一步创建user实体类

public class User {
    private Long id;
    private String username;
    private String passwd;

    public User(int id, String username, String passwd) {
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPasswd() {
        return passwd;
    }

    public void setPasswd(String passwd) {
        this.passwd = passwd;
    }
}

第二步创建Controller类

分别返回 User对象、List集合 和 Map集合

import SpringBootDemo.Entity.User;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@RequestMapping("/json")
@RestController
public class JsonController {

    @RequestMapping("/user")
    public User getUser(){
        return new User(1,"小白","123456");
    }

    @RequestMapping("/list")
    public List getUserList(){
        List userList = new ArrayList<>();
        User user1 = new User(2,"小红","121212");
        User user2 = new User(3,"小黑","1111111");
        userList.add(user1);
        userList.add(user2);
        return userList;
    }

    @RequestMapping("/map")
    public Map getUserMap(){
        Map map = new HashMap<>(3);
        User user = new User(4,"小绿","123123");
        map.put("作者信息",user);
        map.put("家庭地址","中国xxx市");
        return map;
    }
    
}

在页面验证，这里返回的json是Null，不知道啥情况，有知道的师傅麻烦告诉我哦！

2.2、Jackson对null的处理

由于spring boot底层是用Jackson来展现json数据的

希望null变为" "，则需要以下jackson配置类

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;

import java.io.IOException;

@Configuration
public class JacksonConfig {
    @Bean
    @Primary
    @ConditionalOnMissingBean(ObjectMapper.class)

    public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder){
        ObjectMapper objectMapper = builder.createXmlMapper(false).build();
        objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer