如何使用Java Jackson更新JSON文件中的值

Question

My Json file will be something like below. (List(List))

[[0,1759,10.0,20.0,30.0,40.0,50.0,60.0,70.0,590,1759]
[1,1533,10.0,20.0,30.0,40.0,50.0,60.0,70.0,590,1533]
[2,2638,10.0,20.0,30.0,40.0,50.0,60.0,70.0,590,2638]
[3,2639,10.0,20.0,30.0,40.0,50.0,60.0,70.0,590,2639]
[4,2640,10.0,20.0,30.0,40.0,50.0,60.0,70.0,590,2640]]

I want to replace the value in 3rd list (5th index in 3rd list). ie: [2,2638,10.0,20.0,30.0,40.0,50.0,60.0,70.0,590,2638]

and i want to change the value 30.0 as 10.0. How to do this change without getting whole file data.

Answer 1

As far my knowledge I'm afraid that you can't do without reading the whole file if you want use JSON.

Try this can be any help

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.util.List;
import java.util.ListIterator;

import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

/**
 * 
 * @author Ravi P
 */
public class Test {

    public static void main( String[] args ) {

        try {

            List<List<Integer>> jsonParentArr = new ObjectMapper().readValue( new File( "C:\\tmp\\Details.json" ), new TypeReference<List<List<Integer>>>() {
            } ); // read the data from file and form a list

            System.out.println( jsonParentArr.get( 2 ) ); // array values before replacing 30

            ListIterator<Integer> childJsonArr = jsonParentArr.get( 2 ).listIterator(); // get the 3rd array

            while ( childJsonArr.hasNext() ) {

                if ( childJsonArr.next() == 30 ) { // replace if the value to 10.0 if the exsting value is 30

                    childJsonArr.set( 10 );
                }
            }

            System.out.println( jsonParentArr.get( 2 ) ); // array values after replacing 30

            try (BufferedWriter bWriter = new BufferedWriter( new FileWriter( "C:\\tmp\\Details.json" ) )) {

                bWriter.write( jsonParentArr.toString() ); // write back the result to same file

            } catch ( Exception e ) {

                e.printStackTrace();
            }

        } catch ( Exception e ) {

            e.printStackTrace();

        }
    }
}