- I already know how gson works and also know how to enable pretty print.
- I want to use gson and not simplejson.
- The problem I had is that I wasn't able to create a file consisting of a List of Employee objects.
- I've seen every other java threads in stackoverflow, mkyong, google's github and many others sites and I still wasn't able to accomplish this simple thing.
- I already know how to read a file with this specific format but I wasn't able to write it.
- The problem is I was not able to combine all these things together in a program.
- A List of objects in gson with pretty print enabled must have the proper indentation, and every object must be separated with a comma and those objects must be wrapped between [ ] .
- The problem explained with code
:
public class Employee implements Serializable {
private String lastName;
private String address;
private int id;
private String name;
}
I want to create a json file with the exact following content
[
{
"id":1,
"name": "John",
"lastName": "Doe",
"address": "NY City"
},
{
"id":2,
"name": "John",
"lastName": "Doe",
"address": "Canada"
},
{
"id":3,
"name": "John",
"lastName": "Doe",
"address": "Las Vegas"
},
]
- I managed to create and write a json file of Person objects (as gson json Person objects), and read it, but again only as Person objects, where every line is an independent object, not a part of a List or Array of Person objects, like this
{"id":1,"name": "John","last": "Doe","address": "NY City"} {"id":2,"name": "John","last": "Doe","address": "Canada"} {"id":3,"name": "John","last": "Doe","address": "Las Vegas"}
but that's not what I want my final program to do.
- I was also able to hard code a file with the following info and format and successfully obtain the Person objects
[ { "id":1, "name": "John", "lastName": "Doe", "address": "NY City" }, { "id":2, "name": "John", "lastName": "Doe", "address": "Canada" }, { "id":3, "name": "John", "lastName": "Doe", "address": "Las Vegas" }, ]
but I don't know how to create and write this json file with a java program as an array of Person objects, where every Person object is a part of this list or array with pretty print format, as the one I hard coded and am able to read. How can I do that in an elegant way?
EDIT--- Thanks a lot to @Shyam!
This is my final code, hope it helps someone.
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.reflect.TypeToken;
public class TestFileOfGsonWriter {
Gson gson ;
String filePath ;
BufferedReader bufferToReader ;
public TestFileOfGsonWriter()
{
this.filePath =
"C:\\FileOfGsonSingleListOfEmployees\\employees.json" ;
}
public List<Employee> createEmployees()
{
Employee arya = new Employee("Stark", "#81, 2nd main, Winterfell", 2, "Arya");
Employee jon = new Employee("Snow", "#81, 2nd main, Winterfell", 1, "Jon");
Employee sansa = new Employee("Stark", "#81, 2nd main, Winterfell", 3, "Sansa");
List<Employee> employees = new ArrayList<>();
employees.add(jon);
employees.add(arya);
employees.add(sansa);
return employees ;
}
public void jsonWriter(List<Employee> employees, String filePath)
{
this.gson = new GsonBuilder().setPrettyPrinting().create();
try(FileWriter writer = new FileWriter(filePath))
{
gson.toJson(employees,writer);
writer.close();
}
catch(IOException e)
{
e.printStackTrace();
}
}
public void showEmployeeObjects()
{
try {
List<Employee> employees = this.getAllEmployees();
employees.forEach(e -> Employee.showEmployeeDetails(e));
} catch (IOException e) {
e.printStackTrace();
}
}
public ArrayList<Employee> getAllEmployees() throws IOException
{
FileReader reader = new FileReader(this.filePath);
this.bufferToReader = new BufferedReader(reader) ;
ArrayList <Employee> employees = this.gson.fromJson(getJson(),
new TypeToken<ArrayList<Employee>>(){}.getType());
return employees ;
}
private String getJson() throws IOException
{
StringBuilder serializedEmployee = new StringBuilder();
String line ;
while ( (line = this.bufferToReader.readLine()) != null )
{
serializedEmployee.append(line);
}
this.bufferToReader.close();
return serializedEmployee.toString();
}
public static void main(String[] args) {
TestFileOfGsonWriter testWriting = new TestFileOfGsonWriter() ;
List<Employee> employees = testWriting.createEmployees();
testWriting.jsonWriter(employees, testWriting.filePath);
testWriting.showEmployeeObjects();
}
}
I modified my Employee class so it would match with his dummy objects which were better I think, this is how it looks now.
import java.io.Serializable;
public class Employee implements Serializable {
private static final long serialVersionUID = 1L;
String name ;
String address;
String lastName ;
int id ;
public static void showEmployeeDetails(Employee e)
{
System.out.println();
System.out.println("Employee's name: "+e.name);
System.out.println("Employee's last name"+e.lastName);
System.out.println("Employee's address: "+e.address);
System.out.println("Employee's ID: "+e.id);
}
public Employee(String myName, String myAddress, int myId, String myLastName)
{
this.name = myName ;
this.address = myAddress;
this.lastName = myLastName;
this.id = myId ;
}
}
So, the json file the program creates looks exactly how I wanted:
[
{
"name": "Snow",
"address": "#81, 2nd main, Winterfell",
"lastName": "Jon",
"id": 1
},
{
"name": "Stark",
"address": "#81, 2nd main, Winterfell",
"lastName": "Arya",
"id": 2
},
{
"name": "Stark",
"address": "#81, 2nd main, Winterfell",
"lastName": "Sansa",
"id": 3
}
]
and finally, this is the output:
Employee's name: Snow
Employee's last nameJon
Employee's address: #81, 2nd main, Winterfell
Employee's ID: 1
Employee's name: Stark
Employee's last nameArya
Employee's address: #81, 2nd main, Winterfell
Employee's ID: 2
Employee's name: Stark
Employee's last nameSansa
Employee's address: #81, 2nd main, Winterfell
Employee's ID: 3
