How does SpringBoot return Json data format-Java Tutorial-php.cn

1. @RestController annotation

Use the @RestController annotation in the Controller in Spring Boot to return data in JSON format.

@RestController annotation includes @Controller and @ResponseBody annotations.
@ResponseBody Annotation is to convert the returned data structure into JSON format.

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Controller
@ResponseBody
public @interface RestController {
    String value() default "";
}

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2. Jackson

The default JSON parsing technology framework used in Spring Boot is Jackson.

Click on the spring-boot-starter-web dependency in pom.xml, you can see the spring-boot-starter-json dependency:


    org.springframework.boot
    spring-boot-starter-json
    2.0.3.RELEASE
    compile

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Click again on the spring- mentioned above boot-starter-json dependency, you can see the following code:


    com.fasterxml.jackson.core
    jackson-databind
    2.9.6
    compile


    com.fasterxml.jackson.datatype
    jackson-datatype-jdk8
    2.9.6
    compile


    com.fasterxml.jackson.datatype
    jackson-datatype-jsr310
    2.9.6
    compile


    com.fasterxml.jackson.module
    jackson-module-parameter-names
    2.9.6
    compile

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So far, you can know that the default JSON parsing framework used in Spring Boot is Jackson.

1. Convert Object, List, Map to Json format

Create entity class:

public class User {
    private Long id;
    private String username;
    private String password;
    /* 省略get、set和带参构造方法 */
}

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Controller layer

import com.itcodai.course02.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;

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

    @RequestMapping("/user")
    public User getUser() {
        return new User(1, "倪升武", "123456");
        //返回 {"id":1,"username":"倪升武","password":"123456"}
    }

    @RequestMapping("/list")
    public List getUserList() {
        List userList = new ArrayList<>();
        User user1 = new User(1, "倪升武", "123456");
        User user2 = new User(2, "达人课", "123456");
        userList.add(user1);
        userList.add(user2);
        return userList;
        //返回 [{"id":1,"username":"倪升武","password":"123456"},{"id":2,"username":"达人课","password":"123456"}]

    }

    @RequestMapping("/map")
    public Map getMap() {
        Map map = new HashMap<>(3);
        User user = new User(1, "倪升武", "123456");
        map.put("作者信息", user);
        map.put("博客地址", "http://blog.itcodai.com");
        map.put("CSDN地址", "http://blog.csdn.net/eson_15");
        map.put("粉丝数量", 4153);
        return map;
        //返回 {"作者信息":{"id":1,"username":"倪升武","password":"123456"},"CSDN地址":"http://blog.csdn.net/eson_15","粉丝数量":4153,"博客地址":"http://blog.itcodai.com"}

    }
}

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2. Jackson's configuration class

Convert all nulls to "" configuration when converting to JSON format

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