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>

  
 

  
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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"
  }
}

  
 

  
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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();
	}
  
 

  
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【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 List<String> cities;
	private Map<String, 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 List<String> getCities() {
		return cities;
	}
	public void setCities(List<String> cities) {
		this.cities = cities;
	}
	public Map<String, String> getProperties() {
		return properties;
	}
	public void setProperties(Map<String, 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();
	}
}

  
 

  
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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);

		List<String> cities = new ArrayList<String>();
		cities.add("Los Angeles");
		cities.add("New York");
		emp.setCities(cities);

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

		return emp;
	}

}

  
 

  
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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

  
 

  
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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"
}

  
 

  
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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

文章来源: artisan.blog.csdn.net，作者：小小工匠，版权归原作者所有，如需转载，请联系作者。

原文链接：artisan.blog.csdn.net/article/details/115339683