Jackson序列化和反序列化Json数据完整示例

Jackson序列化和反序列化Json数据

Web技术发展的今天，Json和XML已经成为了web数据的事实标准，然而这种格式化的数据手工解析又非常麻烦，软件工程界永远不缺少工具，每当有需求的时候就会出现各种类库，框架以及工具来解决这些基础的问题，Jackson就是这些工具中的一个，使用这个工具开发者完全可以从手工结束Json数据的重复劳动中解放出来。使用Jackson首先需要下载相应的类库，如下的Maven dependency列出了完整的POM dependency。

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>${jackson-2-version}</version>
        </dependency>
        
        <!-- Just the annotations; use this dependency if you want to attach annotations 
            to classes without connecting them to the code. -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>${jackson-2-version}</version>
        </dependency>
    
        <!-- databinding; ObjectMapper, JsonNode and related classes are here -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>${jackson-2-version}</version>
        </dependency>
    
        <!-- smile (binary JSON). Other artifacts in this group do other formats. -->
        <dependency>
            <groupId>com.fasterxml.jackson.dataformat</groupId>
            <artifactId>jackson-dataformat-smile</artifactId>
            <version>${jackson-2-version}</version>
        </dependency>
        <!-- JAX-RS provider -->
        <dependency>
            <groupId>com.fasterxml.jackson.jaxrs</groupId>
            <artifactId>jackson-jaxrs-json-provider</artifactId>
            <version>${jackson-2-version}</version>
        </dependency>
        <!-- Support for JAX-B annotations as additional configuration -->
        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-jaxb-annotations</artifactId>
            <version>${jackson-2-version}</version>
        </dependency>

比如我们需要解析的Json数据如下：

{
  "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"
  }
}

对应的Model Class 如下：

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;
    }

    @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();
    }
    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;
    }
}

当我们需要操作Json数据的时候，如下代码示范了如何将Json数据反序列化为对象以及如何将对象序列化为Json数据。

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;

public class JacksonObjectMapperExample {

    public static void main(String[] args) throws IOException {

        //read json file data to String
        byte[] jsonData = Files.readAllBytes(Paths.get("C:\\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;
    }

}

结果如下：

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
{
  "id" : 100,
  "name" : "David",
  "permanent" : false,
  "address" : {
    "street" : "BTM 1st Stage",
    "city" : "Bangalore",
    "zipcode" : 560100
  },
  "phoneNumbers" : [ 123456, 987654 ],
  "role" : "Manager",
  "cities" : [ "Los Angeles", "New York" ],
  "properties" : {
    "salary" : "1000 Rs",
    "age" : "28 years"
  }
}

总结

本文以一个完整的示例总结了Java对象序列化为Json对象和反序列化的过程，希望可以抛砖引玉对大家有所帮助。