Most efficient conversion of ResultSet to JSON?

user_456850 0
Viewed 193965

The following code converts a ResultSet to a JSON string using JSONArray and JSONObject.

import org.json.JSONArray;
import org.json.JSONObject;
import org.json.JSONException;

import java.sql.SQLException;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;

public class ResultSetConverter {
  public static JSONArray convert( ResultSet rs )
    throws SQLException, JSONException
  {
    JSONArray json = new JSONArray();
    ResultSetMetaData rsmd = rs.getMetaData();

    while(rs.next()) {
      int numColumns = rsmd.getColumnCount();
      JSONObject obj = new JSONObject();

      for (int i=1; i<numColumns+1; i++) {
        String column_name = rsmd.getColumnName(i);

        if(rsmd.getColumnType(i)==java.sql.Types.ARRAY){
         obj.put(column_name, rs.getArray(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.BIGINT){
         obj.put(column_name, rs.getInt(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.BOOLEAN){
         obj.put(column_name, rs.getBoolean(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.BLOB){
         obj.put(column_name, rs.getBlob(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.DOUBLE){
         obj.put(column_name, rs.getDouble(column_name)); 
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.FLOAT){
         obj.put(column_name, rs.getFloat(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.INTEGER){
         obj.put(column_name, rs.getInt(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.NVARCHAR){
         obj.put(column_name, rs.getNString(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.VARCHAR){
         obj.put(column_name, rs.getString(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.TINYINT){
         obj.put(column_name, rs.getInt(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.SMALLINT){
         obj.put(column_name, rs.getInt(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.DATE){
         obj.put(column_name, rs.getDate(column_name));
        }
        else if(rsmd.getColumnType(i)==java.sql.Types.TIMESTAMP){
        obj.put(column_name, rs.getTimestamp(column_name));   
        }
        else{
         obj.put(column_name, rs.getObject(column_name));
        }
      }

      json.put(obj);
    }

    return json;
  }
}
  • Is there a faster way?
  • Is there a way that uses less memory?
resultset sql json java
14 Answers
public static JSONArray GetJSONDataFromResultSet(ResultSet rs) throws SQLException {
    ResultSetMetaData metaData = rs.getMetaData();
    int count = metaData.getColumnCount();
    String[] columnName = new String[count];
    JSONArray jsonArray = new JSONArray();
    while(rs.next()) {
        JSONObject jsonObject = new JSONObject();
        for (int i = 1; i <= count; i++){
               columnName[i-1] = metaData.getColumnLabel(i);
               jsonObject.put(columnName[i-1], rs.getObject(i));
        }
        jsonArray.put(jsonObject);
    }
    return jsonArray;
}
user_119011220

For all who've opted for the if-else mesh solution, please use:

String columnName = metadata.getColumnName(
String displayName = metadata.getColumnLabel(i);
switch (metadata.getColumnType(i)) {
case Types.ARRAY:
    obj.put(displayName, resultSet.getArray(columnName));
    break;
...

Because in case of aliases in your query, the column name and column label are two different things. For example if you execute:

select col1, col2 as my_alias from table

You will get

[
    { "col1": 1, "col2": 2 }, 
    { "col1": 1, "col2": 2 }
]

Rather than:

[
    { "col1": 1, "my_alias": 2 }, 
    { "col1": 1, "my_alias": 2 }
]
user_14482550
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