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>


<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>${jackson-2-version}</version>
</dependency>


<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>${jackson-2-version}</version>
</dependency>


<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-smile</artifactId>
<version>${jackson-2-version}</version>
</dependency>

<dependency>
<groupId>com.fasterxml.jackson.jaxrs</groupId>
<artifactId>jackson-jaxrs-json-provider</artifactId>
<version>${jackson-2-version}</version>
</dependency>

<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,
],
"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。

Jackson序列化和反序列化Json数据

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