JSON 字串轉Java物件 - by Jaskson

以下範例使用Jackson將JSON字串轉回Java物件，再將轉回的Java物件轉成JSON字串。

在Maven的pom.xml加入Jaskson的套件

<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
</dependency>

下面範例中，先建立一段與類別Company及Branch格式與成員名稱相同的JSON字串，然後將其轉換為Company物件。然後再把Company物件轉回JSON字串。

import java.io.IOException;
import java.util.Map;

import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {

    public static void main(String[] args) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        
        String srcJson = 
                "{\"companyName\":\"SmallCompany\","
                + "\"employeeNumber\":100, "
                + "\"branchMap\":{"
                    + "\"Taipei\":{\"branchName\":\"TaipeiBranch\", \"employeeNumber\":20},"
                    + "\"Taoyuan\":{\"branchName\":\"TaoyuanBranch\", \"employeeNumber\":80}"
                + "}"
                + "}";
        // JSON string to Java Object
        Company company = mapper.readValue(srcJson, Company.class);
        
        System.out.println(company);
        
        System.out.println("===================================================");
        
        // Java Object to JSON string
        String jsonString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(company);
        System.out.println(jsonString);
    }
}

class Company {
    
    private String companyName;
    private Integer employeeNumber;
    private Map<String, Branch> branchMap;
    
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("companyName=" + companyName + ",\n");
        sb.append("employeeeNumber=" + employeeNumber + ",\n");
        sb.append("branchMap=" + branchMap);
        return sb.toString();
    }
    
    public String getCompanyName() {
        return companyName;
    }
    public void setCompanyName(String companyName) {
        this.companyName = companyName;
    }
    public Integer getEmployeeNumber() {
        return employeeNumber;
    }
    public void setEmployeeNumber(Integer employeeNumber) {
        this.employeeNumber = employeeNumber;
    }

    public Map<String, Branch> getBranchMap() {
        return branchMap;
    }

    public void setBranchMap(Map<String, Branch> branchMap) {
        this.branchMap = branchMap;
    }
    
}

class Branch {
    
    private String branchName;
    private Integer employeeNumber;
    
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("branchName=" + branchName + ",");
        sb.append("employeeeNumber=" + employeeNumber);
        return sb.toString();
    }
    
    public String getBranchName() {
        return branchName;
    }
    public void setBranchName(String branchName) {
        this.branchName = branchName;
    }
    public Integer getEmployeeNumber() {
        return employeeNumber;
    }
    public void setEmployeeNumber(Integer employeeNumber) {
        this.employeeNumber = employeeNumber;
    }
    
}

印出結果如下

companyName=SmallCompany,
employeeeNumber=100,
branchMap={Taipei=branchName=TaipeiBranch,employeeeNumber=20, Taoyuan=branchName=TaoyuanBranch,employeeeNumber=80}
===================================================
{
  "companyName" : "SmallCompany",
  "employeeNumber" : 100,
  "branchMap" : {
    "Taipei" : {
      "branchName" : "TaipeiBranch",
      "employeeNumber" : 20
    },
    "Taoyuan" : {
      "branchName" : "TaoyuanBranch",
      "employeeNumber" : 80
    }
  }
}

參考：

• Java 物件轉JSON字串
• Jackson Object和JSON字串轉換，搭配 Java 8 Module 來支援Java 8的特性