除了@Jim Cook 的建议之外，还有一个想法是使用开关而不是 if-elses:

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);


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


json.put(obj);
}

提醒一下，if/then 循环比枚举的开关更有效。如果对原始枚举整数有开关，那么它的效率更高，但对变量，If/then 的效率更高，至少对于 Java5、6和7来说是这样。

例如，出于某种原因(在一些性能测试之后)

if (ordinalValue == 1) {
...
} else (ordinalValue == 2 {
...
}

比

switch( myEnum.ordinal() ) {
case 1:
...
break;
case 2:
...
break;
}

I see that a few people are doubting me, so I'll post code here that you can run yourself to see the difference, along with output I have from Java 7. The results of the following code with 10 enum values are as follows. Note the key here is the if/then using an integer value comparing against ordinal constants of the enum, vs. the switch with an enum's ordinal value against the raw int ordinal values, vs. a switch with the enum against each enum name. The if/then with an integer value beat out both other switches, although the last switch was a little faster than the first switch, it was not faster than the if/else.

如果/否则需要23毫秒
转换花了45毫秒
开关2花了30毫秒
比赛总数: 3000000 < br >

package testing;


import java.util.Random;


enum TestEnum {
FIRST,
SECOND,
THIRD,
FOURTH,
FIFTH,
SIXTH,
SEVENTH,
EIGHTH,
NINTH,
TENTH
}


public class SwitchTest {
private static int LOOP = 1000000;
private static Random r = new Random();
private static int SIZE = TestEnum.values().length;


public static void main(String[] args) {
long time = System.currentTimeMillis();
int matches = 0;
for (int i = 0; i < LOOP; i++) {
int j = r.nextInt(SIZE);
if (j == TestEnum.FIRST.ordinal()) {
matches++;
} else if (j == TestEnum.SECOND.ordinal()) {
matches++;
} else if (j == TestEnum.THIRD.ordinal()) {
matches++;
} else if (j == TestEnum.FOURTH.ordinal()) {
matches++;
} else if (j == TestEnum.FIFTH.ordinal()) {
matches++;
} else if (j == TestEnum.SIXTH.ordinal()) {
matches++;
} else if (j == TestEnum.SEVENTH.ordinal()) {
matches++;
} else if (j == TestEnum.EIGHTH.ordinal()) {
matches++;
} else if (j == TestEnum.NINTH.ordinal()) {
matches++;
} else {
matches++;
}
}
System.out.println("If / else took "+(System.currentTimeMillis() - time)+" ms");
time = System.currentTimeMillis();
for (int i = 0; i < LOOP; i++) {
TestEnum te = TestEnum.values()[r.nextInt(SIZE)];
switch (te.ordinal()) {
case 0:
matches++;
break;
case 1:
matches++;
break;
case 2:
matches++;
break;
case 3:
matches++;
break;
case 4:
matches++;
break;
case 5:
matches++;
break;
case 6:
matches++;
break;
case 7:
matches++;
break;
case 8:
matches++;
break;
case 9:
matches++;
break;
default:
matches++;
break;
}
}
System.out.println("Switch took "+(System.currentTimeMillis() - time)+" ms");
time = System.currentTimeMillis();
for (int i = 0; i < LOOP; i++) {
TestEnum te = TestEnum.values()[r.nextInt(SIZE)];
switch (te) {
case FIRST:
matches++;
break;
case SECOND:
matches++;
break;
case THIRD:
matches++;
break;
case FOURTH:
matches++;
break;
case FIFTH:
matches++;
break;
case SIXTH:
matches++;
break;
case SEVENTH:
matches++;
break;
case EIGHTH:
matches++;
break;
case NINTH:
matches++;
break;
default:
matches++;
break;
}
}
System.out.println("Switch 2 took "+(System.currentTimeMillis() - time)+" ms");
System.out.println("Total matches: "+matches);
}
}

如果有人计划使用这个实现，您可能需要 check this out 还有这个

这是我的转换代码:

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


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.getLong(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.REAL) {
obj.put(column_name, rs.getFloat(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.getDouble(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.CHAR) {
obj.put(column_name, rs.getString(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.NCHAR) {
obj.put(column_name, rs.getNString(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.LONGNVARCHAR) {
obj.put(column_name, rs.getNString(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.LONGVARCHAR) {
obj.put(column_name, rs.getString(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.TINYINT) {
obj.put(column_name, rs.getByte(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.SMALLINT) {
obj.put(column_name, rs.getShort(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.TIME) {
obj.put(column_name, rs.getTime(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.TIMESTAMP) {
obj.put(column_name, rs.getTimestamp(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.BINARY) {
obj.put(column_name, rs.getBytes(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.VARBINARY) {
obj.put(column_name, rs.getBytes(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.LONGVARBINARY) {
obj.put(column_name, rs.getBinaryStream(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.BIT) {
obj.put(column_name, rs.getBoolean(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.CLOB) {
obj.put(column_name, rs.getClob(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.NUMERIC) {
obj.put(column_name, rs.getBigDecimal(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.DECIMAL) {
obj.put(column_name, rs.getBigDecimal(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.DATALINK) {
obj.put(column_name, rs.getURL(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.REF) {
obj.put(column_name, rs.getRef(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.STRUCT) {
obj.put(column_name, rs.getObject(column_name)); // must be a custom mapping consists of a class that implements the interface SQLData and an entry in a java.util.Map object.
} else if (rsmd.getColumnType(i) == java.sql.Types.DISTINCT) {
obj.put(column_name, rs.getObject(column_name)); // must be a custom mapping consists of a class that implements the interface SQLData and an entry in a java.util.Map object.
} else if (rsmd.getColumnType(i) == java.sql.Types.JAVA_OBJECT) {
obj.put(column_name, rs.getObject(column_name));
} else {
obj.put(column_name, rs.getString(i));
}
}


json.put(obj);
}


return json;
}
}

对 JSON 导出使用第三方库

你可以使用 JooQ来完成这项工作。您不必使用 jOOQ 的所有特性来利用一些有用的 JDBC 扩展。在这种情况下，只需写下:

String json = DSL.using(connection).fetch(resultSet).formatJSON();

使用的相关 API 方法包括:

• DSLContext.fetch(ResultSet) to convert a JDBC ResultSet into a jOOQ Result.
• Result.formatJSON() 将 jOOQ 结果格式化为 JSON 字符串。

产生的格式如下:

{"fields":[{"name":"field-1","type":"type-1"},
{"name":"field-2","type":"type-2"},
...,
{"name":"field-n","type":"type-n"}],
"records":[[value-1-1,value-1-2,...,value-1-n],
[value-2-1,value-2-2,...,value-2-n]]}

您还可以通过 Result.map(RecordMapper)轻松地创建自己的格式

这实际上与您的代码一样，绕过了 JSON 对象的生成，直接“流”到 StringBuilder中。但是，在这两种情况下，性能开销都应该可以忽略不计。

(免责声明: 我为 jOOQ 背后的公司工作)

改用 SQL/JSON 特性

当然，您不必使用中间件将 JDBC 结果集映射到 JSON。这个问题没有提到需要使用哪种 SQL 方言，但是许多 SQL 方言支持标准的 SQL/JSON 语法，或者类似的语法，例如。

神使

SELECT json_arrayagg(json_object(*))
FROM t

SQL Server

SELECT *
FROM t
FOR JSON AUTO

PostgreSQL

SELECT to_jsonb(array_agg(t))
FROM t

另一方面，这里我使用了 ArrayList 和 Map，所以它不是逐行调用 json 对象，而是在结果集迭代完成之后调用:

 List<Map<String, String>> list = new ArrayList<Map<String, String>>();


ResultSetMetaData rsMetaData = rs.getMetaData();




while(rs.next()){


Map map = new HashMap();
for (int i = 1; i <= rsMetaData.getColumnCount(); i++) {
String key = rsMetaData.getColumnName(i);


String value = null;


if (rsmd.getColumnType(i) == java.sql.Types.VARCHAR) {
value = rs.getString(key);
} else if(rsmd.getColumnType(i)==java.sql.Types.BIGINT)
value = rs.getLong(key);
}




map.put(key, value);
}
list.add(map);




}




json.put(list);

首先预先生成列名，其次使用 rs.getString(i)而不是 rs.getString(column_name)。

以下是这项工作的实施情况:

    /*
* 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;
}

这个答案可能不是最有效的，但肯定是动态的。将本地 JDBC 与 Google 的 Gson 库结合起来，我可以轻松地将 SQL 结果转换为 JSON 流。

我已经包含了转换器、示例 DB 属性文件、 SQL 表生成和一个 Gradle 构建文件(使用了依赖项)。

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);
}
}

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);
}
}

查询助手.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'
}

结果

基本选择

[
{
"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
}
]

中级选择

[
{
"firstName": "John",
"lastName": "Lennon",
"age": 75
},
{
"firstName": "Paul",
"lastName": "McCartney",
"age": 73
},
{
"firstName": "George",
"lastName": "Harrison",
"age": 72
},
{
"firstName": "Ringo",
"lastName": "Starr",
"age": 75
}
]

A simpler solution (based on code in question):

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; i++) {
String column_name = rsmd.getColumnName(i);
obj.put(column_name, rs.getObject(column_name));
}
json.put(obj);
}
return json;

package com.idal.cib;


import java.io.FileWriter;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;


import org.json.simple.JSONArray;
import org.json.simple.JSONObject;


public class DBJsonConverter {


static ArrayList<String> data = new ArrayList<String>();
static Connection conn = null;
static PreparedStatement ps = null;
static ResultSet rs = null;
static String path = "";
static String driver="";
static String url="";
static String username="";
static String password="";
static String query="";


@SuppressWarnings({ "unchecked" })
public static void dataLoad(String path) {
JSONObject obj1 = new JSONObject();
JSONArray jsonArray = new JSONArray();
conn = DatabaseConnector.getDbConnection(driver, url, username,
password);
try {
ps = conn.prepareStatement(query);
rs = ps.executeQuery();
ArrayList<String> columnNames = new ArrayList<String>();
if (rs != null) {
ResultSetMetaData columns = rs.getMetaData();
int i = 0;
while (i < columns.getColumnCount()) {
i++;
columnNames.add(columns.getColumnName(i));
}
while (rs.next()) {
JSONObject obj = new JSONObject();
for (i = 0; i < columnNames.size(); i++) {
data.add(rs.getString(columnNames.get(i)));
{
for (int j = 0; j < data.size(); j++) {
if (data.get(j) != null) {
obj.put(columnNames.get(i), data.get(j));
}else {
obj.put(columnNames.get(i), "");
}
}
}
}


jsonArray.add(obj);
obj1.put("header", jsonArray);
FileWriter file = new FileWriter(path);
file.write(obj1.toJSONString());
file.flush();
file.close();
}
ps.close();
} else {
JSONObject obj2 = new JSONObject();
obj2.put(null, null);
jsonArray.add(obj2);
obj1.put("header", jsonArray);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (conn != null) {
try {
conn.close();
rs.close();
ps.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}


@SuppressWarnings("static-access")
public static void main(String[] args) {
// TODO Auto-generated method stub
driver = "oracle.jdbc.driver.OracleDriver";
url = "jdbc:oracle:thin:@localhost:1521:database";
username = "user";
password = "password";
path = "path of file";
query = "select * from temp_employee";


DatabaseConnector dc = new DatabaseConnector();
dc.getDbConnection(driver,url,username,password);
DBJsonConverter formatter = new DBJsonConverter();
formatter.dataLoad(path);


}


}








package com.idal.cib;


import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;


public class DatabaseConnector {


static Connection conn1 = null;


public static Connection getDbConnection(String driver, String url,
String username, String password) {
// TODO Auto-generated constructor stub
try {


Class.forName(driver);


conn1 = DriverManager.getConnection(url, username, password);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return conn1;
}


}

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;
}

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;
...

因为在查询中使用别名时，列名和列标签是两件不同的事情。例如，如果执行:

select col1, col2 as my_alias from table

You will get

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

而不是:

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