How to convert a Java resultset into JSON?

Question

I have a resultset as a result of a MySQL query using the JDBC connector. So my job is to convert the resultset into a JSON format. So that I can send it to the clientside a

Answer 1

It's pretty easy if you want to use Spring:

@RestController
public class MyController

  @Autowired
  private JdbcTemplate jdbcTemplate;

  @RequestMapping("/")
  List<Map<String,Object>> getAll() {
    return jdbcTemplate.queryForList("select * from my_table");
  }
}

In mvc-dispatcher-servlet.xml, you'd setup your JdbcTemplate like this:

<bean class="org.springframework.jdbc.core.JdbcTemplate" id="jdbcTemplate">
  <property name="dataSource">
    ...data source config...
  </property>
</bean>

Jackson should be in your classpath (ie a Maven dependency).

Answer 2

If you utilizing the Spring' JDBCTemplate for executing stored functions which returns cursor as list of the tables entries and, in turns, you wish to map it as a list of the specified bean, then there is the most neat solution:

import com.fasterxml.jackson.databind.ObjectMapper;

...

final static ObjectMapper mapper = new ObjectMapper();

...

<T> List<T> populateExecuteRetrieve(SimpleJdbcCall call, Map inputParameters, Class<T> outputClass) {
    List<?> sqlResult;
    sqlResult = call.executeFunction(ArrayList.class, parameter);
    return sqlResult
            .stream()
            .map(entry -> mapper.convertValue(entry, outputBeanClass))
            .collect(Collectors.toList());
}

You are welcome!

Happy coding!

Answer 3

I found best solution here.

import org.json.JSONArray;
import org.json.JSONObject;
import java.sql.ResultSet;

/**
 * Convert a result set into a JSON Array
 * @param resultSet
 * @return a JSONArray
 * @throws Exception
 */
public static JSONArray convertToJSON(ResultSet resultSet)
        throws Exception {
    JSONArray jsonArray = new JSONArray();
    while (resultSet.next()) {
        int total_rows = resultSet.getMetaData().getColumnCount();
        for (int i = 0; i < total_rows; i++) {
            JSONObject obj = new JSONObject();
            obj.put(resultSet.getMetaData().getColumnLabel(i + 1)
                    .toLowerCase(), resultSet.getObject(i + 1));
            jsonArray.put(obj);
        }
    }
    return jsonArray;
}

Answer 4

Many people have answered the question correctly. But, I think i can add more value to the post with the following small snippet of code. It uses the Apache-DBUtils and the Gson library.

public static String resultSetToJson(Connection connection, String query) {
        List<Map<String, Object>> listOfMaps = null;
        try {
            QueryRunner queryRunner = new QueryRunner();
            listOfMaps = queryRunner.query(connection, query, new MapListHandler());
        } catch (SQLException se) {
            throw new RuntimeException("Couldn't query the database.", se);
        } finally {
            DbUtils.closeQuietly(connection);
        }
        return new Gson().toJson(listOfMaps);
    }

Answer 5

• Convert resultset into List<Map<String, Object>> (each map contains a row with column names as keys and column content as value, List is a list of such rows)
• Use Gson or Jackson library to covert this object into JSON.

Answer 6

You can use any JSON library.

The following is an implementation of this, return a list, with each element a JSON Object:

/*
 * Convert ResultSet to a common JSON Object array
 * Result is like: [{"ID":"1","NAME":"Tom","AGE":"24"}, {"ID":"2","NAME":"Bob","AGE":"26"}, ...]
 */
public static List<JSONObject> getFormattedResult(ResultSet rs) {
    List<JSONObject> resList = new ArrayList<JSONObject>();
    try {
        // get column names
        ResultSetMetaData rsMeta = rs.getMetaData();
        int columnCnt = rsMeta.getColumnCount();
        List<String> columnNames = new ArrayList<String>();
        for(int i=1;i<=columnCnt;i++) {
            columnNames.add(rsMeta.getColumnName(i).toUpperCase());
        }

        while(rs.next()) { // convert each object to an human readable JSON object
            JSONObject obj = new JSONObject();
            for(int i=1;i<=columnCnt;i++) {
                String key = columnNames.get(i - 1);
                String value = rs.getString(i);
                obj.put(key, value);
            }
            resList.add(obj);
        }
    } catch(Exception e) {
        e.printStackTrace();
    } finally {
        try {
            rs.close();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    return resList;
}