概述

Jackson JSON Java Parser非常流行，并且也用于Spring框架。

Jackson JSON Parser API提供了将JSON转换为POJO对象的简便方法，并支持从JSON数据轻松转换为Map。

Jackson也支持泛型，并直接将它们从JSON转换为对象。

依赖

要在我们的项目中使用Jackson JSON Java API，我们可以将其添加到项目构建路径中

dependency>
    
    groupId>
    com.fasterxml.jackson.core/groupId>
    
    artifactId>
    jackson-databind/artifactId>
    
    version>
    2.2.3/version>
    
/dependency>
    

jackson-databind jar依赖于jackson-core和jackson-annotations库，因此，如果直接将它们添加到构建路径，请确保将所有三个添加在一起，否则会出现运行时错误。

Jackson JSON示例

基础数据

对于从JSON到POJO / Java对象转换的示例，我们将使用一个嵌套对象和数组的复杂示例。、

我们将在Java对象中使用数组，列表和Map进行转换。 json存储在文件employee.txt中，其结构如下

{

  "id": 123,
  "name": "Pankaj",
  "permanent": true,
  "address": {

    "street": "Albany Dr",
    "city": "San Jose",
    "zipcode": 95129
  }
,
  "phoneNumbers": [
    123456,
    987654
  ],
  "role": "Manager",
  "cities": [
    "Los Angeles",
    "New York"
  ],
  "properties": {

    "age": "29 years",
    "salary": "1000 USD"
  }

}
    

有以下与json数据相对应的java类。

【Address 】

public class Address {
    
    
    private String street;
    
    private String city;
    
    private int zipcode;

    
    public String getStreet() {
    
        return street;

    }

    public void setStreet(String street) {
    
        this.street = street;

    }

    public String getCity() {
    
        return city;

    }

    public void setCity(String city) {
    
        this.city = city;

    }

    public int getZipcode() {
    
        return zipcode;

    }

    public void setZipcode(int zipcode) {
    
        this.zipcode = zipcode;

    }

    
    @Override
    public String toString(){
    
        return getStreet() + ", "+getCity()+", "+getZipcode();

    }
    

【Employee 】

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


public class Employee {
    

    private int id;
    
    private String name;
    
    private boolean permanent;
    
    private Address address;
    
    private long[] phoneNumbers;
    
    private String role;
    
    private ListString>
     cities;
    
    private MapString, String>
     properties;

    
    public int getId() {
    
        return id;

    }

    public void setId(int id) {
    
        this.id = id;

    }

    public String getName() {
    
        return name;

    }

    public void setName(String name) {
    
        this.name = name;

    }

    public boolean isPermanent() {
    
        return permanent;

    }

    public void setPermanent(boolean permanent) {
    
        this.permanent = permanent;

    }

    public Address getAddress() {
    
        return address;

    }

    public void setAddress(Address address) {
    
        this.address = address;

    }

    public long[] getPhoneNumbers() {
    
        return phoneNumbers;

    }

    public void setPhoneNumbers(long[] phoneNumbers) {
    
        this.phoneNumbers = phoneNumbers;

    }

    public String getRole() {
    
        return role;

    }

    public void setRole(String role) {
    
        this.role = role;

    }
    
    
    
    public ListString>
 getCities() {
    
        return cities;

    }
    
    public void setCities(ListString>
 cities) {
    
        this.cities = cities;

    }
    
    public MapString, String>
 getProperties() {
    
        return properties;

    }
    
    public void setProperties(MapString, String>
 properties) {
    
        this.properties = properties;

    }


    @Override
    public String toString(){
    
        StringBuilder sb = new StringBuilder();
    
        sb.append("***** Employee Details *****\n");
    
        sb.append("ID="+getId()+"\n");
    
        sb.append("Name="+getName()+"\n");
    
        sb.append("Permanent="+isPermanent()+"\n");
    
        sb.append("Role="+getRole()+"\n");
    
        sb.append("Phone Numbers="+Arrays.toString(getPhoneNumbers())+"\n");
    
        sb.append("Address="+getAddress()+"\n");
    
        sb.append("Cities="+Arrays.toString(getCities().toArray())+"\n");
    
        sb.append("Properties="+getProperties()+"\n");
    
        sb.append("*****************************");
    
        
        return sb.toString();

    }

}
    

Employee是代表根json对象的Java bean。现在，让我们看看如何使用Jackson JSON解析器API将JSON转换为Java对象

JSON转换为Java对象

import java.io.File;
    
import java.io.IOException;
    
import java.io.StringWriter;
    
import java.nio.file.Files;
    
import java.nio.file.Paths;
    
import java.util.ArrayList;
    
import java.util.HashMap;
    
import java.util.Iterator;
    
import java.util.List;
    
import java.util.Map;
    

import com.fasterxml.jackson.core.type.TypeReference;
    
import com.fasterxml.jackson.databind.JsonNode;
    
import com.fasterxml.jackson.databind.ObjectMapper;
    
import com.fasterxml.jackson.databind.SerializationFeature;
    
import com.fasterxml.jackson.databind.node.ObjectNode;
    
import com.journaldev.jackson.model.Address;
    
import com.journaldev.jackson.model.Employee;



public class JacksonObjectMapperExample {


    public static void main(String[] args) throws IOException {
    
        
        //read json file data to String
        byte[] jsonData = Files.readAllBytes(Paths.get("employee.txt"));
    
        
        //create ObjectMapper instance
        ObjectMapper objectMapper = new ObjectMapper();
    
        
        //convert json string to object
        Employee emp = objectMapper.readValue(jsonData, Employee.class);
    
        
        System.out.println("Employee Object\n"+emp);
    
        
        //convert Object to json string
        Employee emp1 = createEmployee();
    
        //configure Object mapper for pretty print
        objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);
    
        
        //writing to console, can write to any output stream such as file
        StringWriter stringEmp = new StringWriter();
    
        objectMapper.writeValue(stringEmp, emp1);
    
        System.out.println("Employee JSON is\n"+stringEmp);

    }

    
    public static Employee createEmployee() {
    

        Employee emp = new Employee();
    
        emp.setId(100);
    
        emp.setName("David");
    
        emp.setPermanent(false);

        emp.setPhoneNumbers(new long[] {
 123456, 987654 }
    );
    
        emp.setRole("Manager");
    

        Address add = new Address();
    
        add.setCity("Bangalore");
    
        add.setStreet("BTM 1st Stage");
    
        add.setZipcode(560100);
    
        emp.setAddress(add);
    

        ListString>
     cities = new ArrayListString>
    ();
    
        cities.add("Los Angeles");
    
        cities.add("New York");
    
        emp.setCities(cities);
    

        MapString, String>
     props = new HashMapString, String>
    ();
    
        props.put("salary", "1000 Rs");
    
        props.put("age", "28 years");
    
        emp.setProperties(props);
    

        return emp;

    }


}
    

输出

Employee Object
***** Employee Details *****
ID=123
Name=Pankaj
Permanent=true
Role=Manager
Phone Numbers=[123456, 987654]
Address=Albany Dr, San Jose, 95129
Cities=[Los Angeles, New York]
Properties={
age=29 years, salary=1000 USD}
    
*****************************
Employee JSON is
//printing same as above json file data

com.fasterxml.jackson.databind.ObjectMapper是Jackson API中最重要的类，它提供readValue（）和writeValue（）方法以将JSON转换为Java Object以及将Java Object转换为JSON。

ObjectMapper类可以重用，并且可以将其作为Singleton对象初始化一次。有很多重载版本的readValue（）和writeValue（）方法可用于字节数组，File，输入/输出流和Reader / Writer对象。

Jackson JSON –将JSON转换为Map

在data.txt文件中有一个如下所示的JSON对象：

{

  "name": "David",
  "role": "Manager",
  "city": "Los Angeles"
}
    

2.2 Jackson JSON –读取特定的JSON密钥

2.3 Jackson JSON –编辑JSON文档

2.4 Jackson JSON流API示例

声明：本文内容由网友自发贡献，本站不承担相应法律责任。对本内容有异议或投诉，请联系2913721942#qq.com核实处理，我们将尽快回复您，谢谢合作！