Published July 30, 2019 by

How to Convert Database Results into JSON Files











Pre-Requisite:

Create Mock Table "constomersInfo" in "ClassicModels" Database and insert some data.

CREATE DATABASE ClassicModels;
use ClassicModels;

CREATE TABLE CustomerInfo

(BookName varchar(50),
PurchasedDate date,
Amount int(50),
Location varchar(50));

INSERT INTO CustomerInfo values("selenium",CURRENT_DATE(),350,'Africa');
INSERT INTO CustomerInfo values("Java",CURRENT_DATE(),200,'Africa');
INSERT INTO CustomerInfo values("Python",CURRENT_DATE(),250,'Asia');
INSERT INTO CustomerInfo values("Jmeter",CURRENT_DATE(),150,'Asia');
INSERT INTO CustomerInfo values("C#",CURRENT_DATE(),300,'Asia');
select * from CustomerInfo where purchasedDate=CURDATE() and Location ='Asia';

Step 1: Retrieve Results from Database using JDBC

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class ConvertDBResult_JavaObject_JsonFile{

     public static void main(String[] args) throws SQLException {
          // 1) Create a connection
          Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels", "root", "root");

          // 2) Create statement/Query
          Statement stmt = con.createStatement();

          String s = "select * from customerinfo  limit 1";

          // 3,4) Execute statement/Query & Store data in resultset
          ResultSet rs = stmt.executeQuery(s);

          CustomerDetails cd=new CustomerDetails();
         
          while (rs.next()) {
              String bookname = rs.getString("BookName");
              String purchasedate = rs.getString("PurchasedDate");
              int amount = rs.getInt("Amount");
              String location = rs.getString("Location");
              System.out.println(bookname + "   " + purchasedate + "      " + amount+"    "+location);
          }

          // 5) close connection
          con.close();

          System.out.println("Query executed.....");
     }

}

Step 2: Converts Data base Results into Java Object (Plain Old Java Object)  public class CustomerDetails {
     String bookname;
     String purchasedate;
     int amount;
     String location;
    
     public String getBookname() {
          return bookname;
     }
     public void setBookname(String bookname) {
          this.bookname = bookname;
     }
     public String getPurchasedate() {
          return purchasedate;
     }
     public void setPurchasedate(String purchasedate) {
          this.purchasedate = purchasedate;
     }
     public int getAmount() {
          return amount;
     }
     public void setAmount(int amount) {
          this.amount = amount;
     }
     public String getLocation() {
          return location;
     }
     public void setLocation(String location) {
          this.location = location;
     }
}

Modify JDBC Program which will use POJO (Plain Old Java Object) Class to retrieve data from Java Object.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class ConvertDBResult_JavaObject_JsonFile{

     public static void main(String[] args) throws SQLException {
          // 1) Create a connection
          Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels", "root", "root");

          // 2) Create statement/Query
          Statement stmt = con.createStatement();

          String s = "select * from customerinfo  limit 1";

          // 3,4) Execute statement/Query & Store data in resultset
          ResultSet rs = stmt.executeQuery(s);

          CustomerDetails cd=new CustomerDetails();
         
          while (rs.next()) {
              String bookname = rs.getString("BookName");
              String purchasedate = rs.getString("PurchasedDate");
              int amount = rs.getInt("Amount");
              String location = rs.getString("Location");
             
              cd.setBookname(bookname);
              cd.setPurchasedate(purchasedate);
              cd.setAmount(amount);
              cd.setLocation(location);
          }

          // 5) close connection
          con.close();
    
          System.out.println(cd.getLocation());
     }
}

Step 3: Convert Java Objects into JSON Files
            Maven Dependencies: Jackson Core, Jackson Databind, Jackson annotations

Single Java Object à Single JSON File:

import java.io.File;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class ConvertDBResult_JavaObject_JsonFile{

     public static void main(String[] args) throws SQLException, JsonGenerationException, JsonMappingException, IOException {
          // 1) Create a connection
          Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels", "root", "root");

          // 2) Create statement/Query
          Statement stmt = con.createStatement();

          String s = "select * from customerinfo  limit 1";

          // 3,4) Execute statement/Query & Store data in resultset
          ResultSet rs = stmt.executeQuery(s);

          CustomerDetails cd=new CustomerDetails();
         
          while (rs.next()) {
              String bookname = rs.getString("BookName");
              String purchasedate = rs.getString("PurchasedDate");
              int amount = rs.getInt("Amount");
              String location = rs.getString("Location");
             
              cd.setBookname(bookname);
              cd.setPurchasedate(purchasedate);
              cd.setAmount(amount);
              cd.setLocation(location);
          }

          // 5) close connection
          con.close();
                  
          // Using Jakson API, Converting Java object into JSON File
          File jsonfile=new File("C:\\Users\\admin\\eclipse-workspace\\sdet\\custinfo.json");
         
          ObjectMapper om=new ObjectMapper();
          om.writeValue(jsonfile, cd);
         
          System.out.println("Done!");
         
     }

}

Multiple Java Objects à Multiple JSON Files:

import java.io.File;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class ConvertDBResults_JavaObjects_JsonFiles {

     public static void main(String[] args) throws SQLException, JsonGenerationException, JsonMappingException, IOException {
          // 1) Create a connection
          Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels", "root", "root");

          // 2) Create statement/Query
          Statement stmt = con.createStatement();

          String s = "select * from customerinfo";

          // 3,4) Execute statement/Query & Store data in resultset
          ResultSet rs = stmt.executeQuery(s);

          ArrayList ar=new ArrayList();
         
          while (rs.next()) {
              String bookname = rs.getString("BookName");
              String purchasedate = rs.getString("PurchasedDate");
              int amount = rs.getInt("Amount");
              String location = rs.getString("Location");
             
              CustomerDetails cd=new CustomerDetails();
             
              cd.setBookname(bookname);
              cd.setPurchasedate(purchasedate);
              cd.setAmount(amount);
              cd.setLocation(location);
             
              ar.add(cd); // Adding all the objects to arraylist
          }

          //Using Jakson API, Converting all Java objects into JSON Files
         
          for(int i=0;i
          {
              File jsonfile=new File("C:\\Users\\admin\\eclipse-workspace\\sdet\\custinfo"+i+".json");
             
              ObjectMapper om=new ObjectMapper();
              om.writeValue(jsonfile,ar.get(i));
          }
                  
          System.out.println("Done!");
    
          con.close();
         
     }

}

Multiple Java Objects à Single JSON (Along with JSON Formatting):

package sdet;

import java.io.File;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;

import org.json.simple.JSONArray;
import org.json.simple.JSONObject;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.gson.Gson;

public class ConvertDBResults_JavaObjects_SingleJsonFile {

     public static void main(String[] args) throws SQLException, JsonGenerationException, JsonMappingException, IOException {
          // 1) Create a connection
          Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/classicmodels", "root", "root");

          // 2) Create statement/Query
          Statement stmt = con.createStatement();

          String s = "select * from customerinfo";

          // 3,4) Execute statement/Query & Store data in resultset
          ResultSet rs = stmt.executeQuery(s);

          ArrayList ar=new ArrayList();
         
          while (rs.next()) {
              String bookname = rs.getString("BookName");
              String purchasedate = rs.getString("PurchasedDate");
              int amount = rs.getInt("Amount");
              String location = rs.getString("Location");
             
              CustomerDetails cd=new CustomerDetails();
             
              cd.setBookname(bookname);
              cd.setPurchasedate(purchasedate);
              cd.setAmount(amount);
              cd.setLocation(location);
             
              ar.add(cd); // Adding all the objects to arraylist
          }

          //Using Jakson API, Converting all Java objects into JSON Files
         
          JSONArray jsonr=new JSONArray(); //Required to add JSon string to Json array
         
          for(int i=0;i
          {
              //File jsonfile=new File("C:\\Users\\admin\\eclipse-workspace\\sdet\\custinfo"+i+".json");
              //ObjectMapper om=new ObjectMapper();
              //om.writeValue(jsonfile,ar.get(i));
             
              Gson g=new Gson();
              String JsonString=g.toJson(ar.get(i)); //Converts Java object into JSON String
             
              jsonr.add(JsonString); //Add JSon String to Json Array
          }
         
          JSONObject jo=new JSONObject();
          jo.put("data",jsonr);
         
          System.out.println(jo.toJSONString()); // added escape chars That's not right format
    
          String jsonFormattedString = jo.toJSONString().replace("\\\"", "\""); //removed escape chars
          System.out.println(jsonFormattedString); //still doubles quotes there. It's not exactly in Json format
         
          String finalJSONString=jsonFormattedString.replace("\"{","{").replace("}\"","}"); //Removes double quotes both the sides
          System.out.println(finalJSONString);
         
          System.out.println("Done!");
                  
          con.close();
         
     }

}

Step 4: Convert JSON to Java Object
import java.io.File;
import java.io.IOException;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class JSONtoJavaObject {

     public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
         
          ObjectMapper om=new ObjectMapper();
         
          File jsonfile=new File("C:\\Users\\admin\\eclipse-workspace\\sdet\\custinfo.json");
          CustomerDetails cd=om.readValue(jsonfile, CustomerDetails.class);
         
          System.out.println(cd.getBookname());
          System.out.println(cd.getAmount());
         

     }

}

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