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。

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        com.fasterxml.jackson.core
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        jackson-core
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        ${jackson-2-version}
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       6          7         
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        com.fasterxml.jackson.core
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        jackson-annotations
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        ${jackson-2-version}
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        com.fasterxml.jackson.core
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        jackson-databind
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        ${jackson-2-version}
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        com.fasterxml.jackson.dataformat
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        jackson-dataformat-smile
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        ${jackson-2-version}
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        com.fasterxml.jackson.jaxrs
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        jackson-jaxrs-json-provider
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        ${jackson-2-version}
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      34         
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        com.fasterxml.jackson.module
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        jackson-module-jaxb-annotations
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        ${jackson-2-version}
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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
     
       cities;    private Map
      
        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
       
         getCities() {        return cities;    }    public void setCities(List
        
          cities) {        this.cities = cities;    }    public Map
         
           getProperties() {        return properties;    }    public void setProperties(Map
          
            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
     
       cities = new ArrayList
      
       ();        cities.add("Los Angeles");        cities.add("New York");        emp.setCities(cities);         Map
       
         props = new HashMap
        
         ();        props.put("salary", "1000 Rs");        props.put("age", "28 years");        emp.setProperties(props);         return emp;    } }
        
       
      
     

结果如下：

Employee Object***** Employee Details *****ID=123Name=PankajPermanent=trueRole=ManagerPhone Numbers=[123456, 987654]Address=Albany Dr, San Jose, 95129Cities=[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。