This answer may not be the most efficient, but it sure is dynamic. Pairing native JDBC with Google's Gson library, I easily can convert from an SQL result to a JSON stream.
I have included the converter, example DB properties file, SQL table generation, and a Gradle build file (with dependencies used).
QueryApp.java
import java.io.PrintWriter;
import com.oracle.jdbc.ResultSetConverter;
public class QueryApp {
public static void main(String[] args) {
PrintWriter writer = new PrintWriter(System.out);
String dbProps = "/database.properties";
String indent = " ";
writer.println("Basic SELECT:");
ResultSetConverter.queryToJson(writer, dbProps, "SELECT * FROM Beatles", indent, false);
writer.println("\n\nIntermediate SELECT:");
ResultSetConverter.queryToJson(writer, dbProps, "SELECT first_name, last_name, getAge(date_of_birth) as age FROM Beatles", indent, true);
}
}
ResultSetConverter.java
package com.oracle.jdbc;
import java.io.*;
import java.lang.reflect.Type;
import java.sql.*;
import java.util.*;
import com.google.common.reflect.TypeToken;
import com.google.gson.GsonBuilder;
import com.google.gson.stream.JsonWriter;
public class ResultSetConverter {
public static final Type RESULT_TYPE = new TypeToken<List<Map<String, Object>>>() {
private static final long serialVersionUID = -3467016635635320150L;
}.getType();
public static void queryToJson(Writer writer, String connectionProperties, String query, String indent, boolean closeWriter) {
Connection conn = null;
Statement stmt = null;
GsonBuilder gson = new GsonBuilder();
JsonWriter jsonWriter = new JsonWriter(writer);
if (indent != null) jsonWriter.setIndent(indent);
try {
Properties props = readConnectionInfo(connectionProperties);
Class.forName(props.getProperty("driver"));
conn = openConnection(props);
stmt = conn.createStatement();
gson.create().toJson(QueryHelper.select(stmt, query), RESULT_TYPE, jsonWriter);
if (closeWriter) jsonWriter.close();
stmt.close();
conn.close();
} catch (SQLException se) {
se.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
try {
if (stmt != null) stmt.close();
} catch (SQLException se2) {
}
try {
if (conn != null) conn.close();
} catch (SQLException se) {
se.printStackTrace();
}
try {
if (closeWriter && jsonWriter != null) jsonWriter.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
private static Properties readConnectionInfo(String resource) throws IOException {
Properties properties = new Properties();
InputStream in = ResultSetConverter.class.getResourceAsStream(resource);
properties.load(in);
in.close();
return properties;
}
private static Connection openConnection(Properties connectionProperties) throws IOException, SQLException {
String database = connectionProperties.getProperty("database");
String username = connectionProperties.getProperty("username");
String password = connectionProperties.getProperty("password");
return DriverManager.getConnection(database, username, password);
}
}
QueryHelper.java
package com.oracle.jdbc;
import java.sql.*;
import java.text.*;
import java.util.*;
import com.google.common.base.CaseFormat;
public class QueryHelper {
static DateFormat DATE_FORMAT = new SimpleDateFormat("YYYY-MM-dd");
public static List<Map<String, Object>> select(Statement stmt, String query) throws SQLException {
ResultSet resultSet = stmt.executeQuery(query);
List<Map<String, Object>> records = mapRecords(resultSet);
resultSet.close();
return records;
}
public static List<Map<String, Object>> mapRecords(ResultSet resultSet) throws SQLException {
List<Map<String, Object>> records = new ArrayList<Map<String, Object>>();
ResultSetMetaData metaData = resultSet.getMetaData();
while (resultSet.next()) {
records.add(mapRecord(resultSet, metaData));
}
return records;
}
public static Map<String, Object> mapRecord(ResultSet resultSet, ResultSetMetaData metaData) throws SQLException {
Map<String, Object> record = new HashMap<String, Object>();
for (int c = 1; c <= metaData.getColumnCount(); c++) {
String columnType = metaData.getColumnTypeName(c);
String columnName = formatPropertyName(metaData.getColumnName(c));
Object value = resultSet.getObject(c);
if (columnType.equals("DATE")) {
value = DATE_FORMAT.format(value);
}
record.put(columnName, value);
}
return record;
}
private static String formatPropertyName(String property) {
return CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, property);
}
}
database.properties
driver=com.mysql.jdbc.Driver
database=jdbc:mysql://localhost/JDBC_Tutorial
username=root
password=
JDBC_Tutorial.sql
-- phpMyAdmin SQL Dump
-- version 4.5.1
-- http://www.phpmyadmin.net
--
-- Host: 127.0.0.1
-- Generation Time: Jan 12, 2016 at 07:40 PM
-- Server version: 10.1.8-MariaDB
-- PHP Version: 5.6.14
SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";
/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8mb4 */;
--
-- Database: `jdbc_tutorial`
--
CREATE DATABASE IF NOT EXISTS `jdbc_tutorial` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci;
USE `jdbc_tutorial`;
DELIMITER $$
--
-- Functions
--
DROP FUNCTION IF EXISTS `getAge`$$
CREATE DEFINER=`root`@`localhost` FUNCTION `getAge` (`in_dob` DATE) RETURNS INT(11) NO SQL
BEGIN
DECLARE l_age INT;
IF DATE_FORMAT(NOW(),'00-%m-%d') >= DATE_FORMAT(in_dob,'00-%m-%d') THEN
-- This person has had a birthday this year
SET l_age=DATE_FORMAT(NOW(),'%Y')-DATE_FORMAT(in_dob,'%Y');
ELSE
-- Yet to have a birthday this year
SET l_age=DATE_FORMAT(NOW(),'%Y')-DATE_FORMAT(in_dob,'%Y')-1;
END IF;
RETURN(l_age);
END$$
DELIMITER ;
-- --------------------------------------------------------
--
-- Table structure for table `beatles`
--
DROP TABLE IF EXISTS `beatles`;
CREATE TABLE IF NOT EXISTS `beatles` (
`id` int(11) NOT NULL,
`first_name` varchar(255) DEFAULT NULL,
`last_name` varchar(255) DEFAULT NULL,
`date_of_birth` date DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
--
-- Truncate table before insert `beatles`
--
TRUNCATE TABLE `beatles`;
--
-- Dumping data for table `beatles`
--
INSERT INTO `beatles` (`id`, `first_name`, `last_name`, `date_of_birth`) VALUES(100, 'John', 'Lennon', '1940-10-09');
INSERT INTO `beatles` (`id`, `first_name`, `last_name`, `date_of_birth`) VALUES(101, 'Paul', 'McCartney', '1942-06-18');
INSERT INTO `beatles` (`id`, `first_name`, `last_name`, `date_of_birth`) VALUES(102, 'George', 'Harrison', '1943-02-25');
INSERT INTO `beatles` (`id`, `first_name`, `last_name`, `date_of_birth`) VALUES(103, 'Ringo', 'Starr', '1940-07-07');
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
build.gradle
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'application'
mainClassName = 'com.oracle.jdbc.QueryApp'
repositories {
maven {
url "http://repo1.maven.org/maven2"
}
}
jar {
baseName = 'jdbc-tutorial'
version = '1.0.0'
}
sourceCompatibility = 1.7
targetCompatibility = 1.7
dependencies {
compile 'mysql:mysql-connector-java:5.1.16'
compile 'com.google.guava:guava:18.0'
compile 'com.google.code.gson:gson:1.7.2'
}
task wrapper(type: Wrapper) {
gradleVersion = '2.9'
}
Results
Basic SELECT
[
{
"firstName": "John",
"lastName": "Lennon",
"dateOfBirth": "1940-10-09",
"id": 100
},
{
"firstName": "Paul",
"lastName": "McCartney",
"dateOfBirth": "1942-06-18",
"id": 101
},
{
"firstName": "George",
"lastName": "Harrison",
"dateOfBirth": "1943-02-25",
"id": 102
},
{
"firstName": "Ringo",
"lastName": "Starr",
"dateOfBirth": "1940-07-07",
"id": 103
}
]
Intermediate SELECT
[
{
"firstName": "John",
"lastName": "Lennon",
"age": 75
},
{
"firstName": "Paul",
"lastName": "McCartney",
"age": 73
},
{
"firstName": "George",
"lastName": "Harrison",
"age": 72
},
{
"firstName": "Ringo",
"lastName": "Starr",
"age": 75
}
]
