jackson简单使用案例

新建Maven项目导入依赖包：jakson

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>henu.yyq</groupId>
    <artifactId>mytest</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <dependencies>
        <!-- jakson依赖包 因为jackson-databind依赖core和annotation俩jar包，所以maven会自动导入--> 
        <!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.9.4</version>
        </dependency>
    </dependencies>
    
        <!-- Jre版本号 -->
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>    

实体类准备

package henu.yyq.jakson;

import java.util.Date;

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;

//空值不序列化：ignoreUnknown=true
//忽略字段：value={"id", ...}
@JsonIgnoreProperties(ignoreUnknown=true, value={"id"})
public class Exam {
    private Integer id;

    private String subject;

    @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss")
    private Date starttime;

    //类型转换
    @JsonFormat(pattern="yyyy-MM-dd HH:mm:ss")
    private Date endtime;

    private String state;
    
    //声明别名
    @JsonProperty("teacherId")
    private String t_id;

    public String getT_id() {
        return t_id;
    }

    public void setT_id(String t_id) {
        this.t_id = t_id;
    }

    public Integer getId() {
        return id;
    }

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

    public String getSubject() {
        return subject;
    }

    public void setSubject(String subject) {
        this.subject = subject == null ? null : subject.trim();
    }

    public Date getStarttime() {
        return starttime;
    }

    public void setStarttime(Date starttime) {
        this.starttime = starttime;
    }

    public Date getEndtime() {
        return endtime;
    }

    public void setEndtime(Date endtime) {
        this.endtime = endtime;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state == null ? null : state.trim();
    }

    @Override
    public String toString() {
        return "Exam [subject=" + subject + ", starttime=" + starttime + ", state=" + state + "]";
    }

}

package henu.yyq.jakson;

import java.util.List;
import java.util.Map;

public class TT {

    private List<Map> lm;

    public List<Map> getLm() {
        return lm;
    }

    public void setLm(List<Map> lm) {
        this.lm = lm;
    }

    @Override
    public String toString() {
        return "TT [lm=" + lm + "]";
    }
    
}

工具类以及测试

package henu.yyq.jakson;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.junit.Test;

import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.ObjectMapper;

/**
 * @ClassName: JsonUtil <br/> 
 * @Describtion: JSON与Java Bean之间的转换. <br/> 
 * @date: 2018年4月17日 下午10:29:39 <br/> 
 * @author Beats <br/> 
 * @version v1.0
 */
public class JsonUtil {

     // 定义ObjectMapper对象，用于数据转换
    private static final ObjectMapper mapper = new ObjectMapper();
    
    /**
     * getJSON:(对象转换成JSON). <br/> 
     * @param bean
     * @return String
     */
    public static String getJson(Object object) {
        try {
            return mapper.writeValueAsString(object);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * getBean:(JSON字符串转对象). <br/> 
     * @param json
     * @param t
     * @return T
     */
    public static <T> T getBean(String json, Class<T> t) {
        try {
            return mapper.readValue(json, t);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    
    /**
     * jsonToObject:(JSON字符串转对象). <br/> 
     * @param json
     * @param t
     * @return T
     */
    public static <T> List<T> getBeanList(String json, Class<T> beanType) {
        try {
            //方案一：
//            JavaType javaType = mapper.getTypeFactory().constructCollectionType(List.class, beanType);
            //方案二：
            JavaType javaType = mapper.getTypeFactory().constructParametricType(List.class, beanType);
            return mapper.readValue(json, javaType);
            //方案三
//            TypeReference<T> typeReference = new TypeReference<T>() {};
//            return mapper.readValue(json, typeReference);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
    
    @Test
    public void testGetJson() {
        //简单类型
        Exam e = new Exam();
        e.setId(100);
        e.setSubject("English");
        e.setState("Created");
        e.setStarttime(new Date());
        e.setEndtime(new Date());
        e.setT_id("1234567890");
        
        String json = JsonUtil.getJson(e);
        System.out.println(json);
        
        //复杂类型
        TT t = new TT();
        
        List<Map> l = new ArrayList<Map>();
        Map m = new HashMap();
        m.put("A", "what's your name");
        l.add(m);
        Map m2 = new HashMap();
        m2.put("B", "what's your mather");
        l.add(m2);
        
        t.setLm(l);
        
        String res = JsonUtil.getJson(t);
        System.out.println(res);
    }
    
    @Test
    public void testGetBean() {
        String json = "{"subject":"English","starttime":"2018-04-17 15:05:01","endtime":"2018-04-17 15:05:01","state":"Created","teacherId":"1234567890"}";
        Exam e = JsonUtil.getBean(json, Exam.class);
        System.out.println(e.toString());
        
        String json2 = "{"lm":[{"A":"what's your name"},{"B":"what's your mather"}]}";
        TT t = JsonUtil.getBean(json2, TT.class);
        System.out.println(t);
    }
    
    @Test
    public void testGetBeanList() {
        String json = "[{"subject":"English","starttime":"2018-04-17 15:05:01","endtime":"2018-04-17 15:05:01","state":"Created","teacherId":"1234567890"},{"subject":"English","starttime":"2018-04-17 15:05:01","endtime":"2018-04-17 15:05:01","state":"Created","teacherId":"1234567890"}]";
        List<Exam> es = JsonUtil.getBeanList(json, Exam.class);
        System.out.println(es);
        
    }
}

结果自己试试就知道了