JDBC封装
前言
正如在前面的小节中看到的，原生的JDBC的操作其实是比较繁琐的，而且其中有很多的重复性代码，这个时候，我们可以考虑自己对JDBC进行一个简单的封装，封装成自己想要的，比较方便的小工具
封装JDBC
为了使得编辑参数更加方便，首先将数据库连接参数抽取出来放在配置文件jdcb.properties中
jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/spring
jdbc.user=root
jdbc.password=huanfeng
然后在类加载的时候加载该配置文件，并且注册驱动类信息
private static Properties properties;
// 使用静态代码块保证在类加载的时候立即加载对应的配置文件
static {
properties = new Properties();
try {
InputStream ins = JDBCUtils.class.getClassLoader().getResourceAsStream("jdbc.properties");
properties.load(ins);
System.out.println("load config file finish");
Class.forName(properties.getProperty("jdbc.driver"));
} catch (FileNotFoundException e) {
System.out.println("jdbc config file not found " + e.getMessage());
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
System.out.println("jdbc class not found " + e.getMessage());
}
}
接着封装获取连接对象getConnection()
/**
* 获得数据库连接Connection
* @return Connection 数据库连接
*/
private static Connection getConnection(){
Connection connection = null;
try {
connection = DriverManager.getConnection(
properties.getProperty("jdbc.url"),
properties.getProperty("jdbc.user"),
properties.getProperty("jdbc.password"));
} catch (SQLException e) {
System.out.println("cannot get connection " + e.getMessage());
}
return connection;
}
然后封装关闭各种资源的方法close()
/**
* 关闭connection
* @param connection 连接池对象
*/
private static void close(Connection connection){
if (connection != null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**
* 关闭Statement
* @param statement
*/
private static void close(Statement statement){
if (statement != null){
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**
* 关闭ResultSet
* @param resultSet
*/
private static void close(ResultSet resultSet){
if (resultSet != null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**
* 关闭Connection 以及Statement
* @param connection
* @param statement
*/
private static void close(Connection connection, Statement statement){
close(connection);
close(statement);
}
/**
* 关闭Connection，Statement以及ResultSet
* @param connection
* @param statement
* @param resultSet
*/
private static void close(Connection connection, Statement statement, ResultSet resultSet){
close(connection, statement);
close(resultSet);
}
接着封装更新方法，正如所知道的，更新包括插入、删除、修改，所以可以将这些操作封装在一个方法即可
/**
* 更新操作
* @param sql 执行的SQL语句
* @param param 对应的参数列表
* @return true 更新成功， false 更新失败
*/
public static boolean update(String sql, Object[] param){
PreparedStatement preparedStatement = null;
Connection connection = getConnection();
try {
preparedStatement = connection.prepareStatement(sql);
if (settingParams(preparedStatement, param) == false){
return false;
}
int result = preparedStatement.executeUpdate();
if (result > 0){
return true;
}
return false;
} catch (SQLException e) {
e.printStackTrace();
}finally {
close(connection, preparedStatement);
}
return false;
}
上面封装了一个方法settingParams()，作用是利用元数据信息，根据SQL语句中的占位符个数，将对应的参数注入进去
/**
* 设置参数
* @param preparedStatement Statement对象
* @param param 参数列表
* @return
* @throws SQLException
*/
private static boolean settingParams(PreparedStatement preparedStatement, Object[] param) throws SQLException {
if (param != null && param.length > 0){
// 获取ParameterMetaData
ParameterMetaData parameterMetaData = preparedStatement.getParameterMetaData();
// 获得SQL中占位符个数
int paramCount = parameterMetaData.getParameterCount();
// 占位符个数与参数个数不一致，返回false表示出错
if (paramCount != param.length){
return false;
}
// 设置对应的参数信息
for (int i = 0; i < paramCount; i++){
preparedStatement.setObject(i+1, param[i]);
}
}
return true;
}
由于查询返回的类型非常多，这里只是封装两个常用的方法，一个是queryForBean()返回单个对象，一个是queryForList()返回List，这里需要注意的是，由于只是简单的封装，所以没有做对象属性名与数据表列名的映射，所以需要保证属性名与列名相同，为了更加方便进行操作，使用了泛型机制，并且使用了Apache的BeanUtils工具进行属性的注入操作,BeanUtils的Maven配置如下所示
commons-beanutils
commons-beanutils
1.9.3
/**
* 获取单个Bean
* @param sql 执行SQL语句
* @param param 对应的参数列表
* @param clazz 所要获取的对象的类型
* @param 对象的类型
* @return
*/
public static T queryForBean(String sql, Object[] param, Class clazz){
Connection connection = getConnection();
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
preparedStatement = connection.prepareStatement(sql);
if (settingParams(preparedStatement, param) == false){
return null;
}
resultSet = preparedStatement.executeQuery();
if (resultSet == null){
return null;
}
if (resultSet.next()){
// 利用反射机制创建对象
T data = clazz.newInstance();
// 获得ResultSetMetaData
ResultSetMetaData resultSetMetaData = resultSet.getMetaData();
// 获得列的数量
int columnCount = resultSetMetaData.getColumnCount();
for (int i = 0; i < columnCount; i++){
// 获得对应的列的名称
String name = resultSetMetaData.getColumnName(i + 1);
// 获得对应的列的值
Object rData = resultSet.getObject(name);
// 使用BeanUtils工具对属性进行注入
BeanUtils.copyProperty(data, name, rData);
}
return data;
}else {
return null;
}
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} finally {
close(connection, preparedStatement, resultSet);
}
return null;
}
/**
* 获取Bean并且封装成List
* @param sql 执行SQL语句
* @param param 对应的参数列表
* @param clazz 所要获取的对象的类型
* @param 对象的类型
* @return list
*/
public static List queryForList(String sql, Object[] param, Class clazz){
Connection connection = getConnection();
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
preparedStatement = connection.prepareStatement(sql);
if (settingParams(preparedStatement, param) == false){
return null;
}
resultSet = preparedStatement.executeQuery();
if (resultSet == null){
return null;
}
List results = new ArrayList<>();
while (resultSet.next()){
// 创建对象
T data = clazz.newInstance();
// 获得ResultSetMetaData
ResultSetMetaData resultSetMetaData = resultSet.getMetaData();
// 获得列的数量
int columnCount = resultSetMetaData.getColumnCount();
for (int i = 0; i < columnCount; i++){
// 获得对应的列的名称
String name = resultSetMetaData.getColumnName(i + 1);
// 获得对应的列的值
Object rData = resultSet.getObject(name);
// 使用BeanUtils工具对属性进行注入
BeanUtils.copyProperty(data, name, rData);
}
results.add(data);
}
return results;
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} finally {
close(connection, preparedStatement, resultSet);
}
return null;
}
至此，通过简单的封装，一个简单的JDBC操作工具就封装好了，这样，当需要的时候就可以非常方便地使用了，而且，当需要其他返回类型的时候，基本上只要按照上面的思路进行处理即可。
完整的代码如下所示
package cn.xuhuanfeng.jdbc;
import org.apache.commons.beanutils.BeanUtils;
import java.io.*;
import java.lang.reflect.InvocationTargetException;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
/**
* Created by Huanfeng.Xu on 2017-07-09.
*/
public class JDBCUtils {
private static Properties properties;
static {
properties = new Properties();
try {
InputStream inputStream = JDBCUtils.class.getResourceAsStream("jdbc.properties");
InputStream ins = JDBCUtils.class.getClassLoader().getResourceAsStream("jdbc.properties");
properties.load(ins);
System.out.println("load config file finish");
Class.forName(properties.getProperty("jdbc.driver"));
} catch (FileNotFoundException e) {
System.out.println("jdbc config file not found " + e.getMessage());
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
System.out.println("jdbc class not found " + e.getMessage());
}
}
/**
* 获得数据库连接Connection
* @return Connection 数据库连接
*/
private static Connection getConnection(){
Connection connection = null;
try {
connection = DriverManager.getConnection(
properties.getProperty("jdbc.url"),
properties.getProperty("jdbc.user"),
properties.getProperty("jdbc.password"));
} catch (SQLException e) {
System.out.println("cannot get connection " + e.getMessage());
}
return connection;
}
/**
* 设置参数
* @param preparedStatement Statement对象
* @param param 参数列表
* @return
* @throws SQLException
*/
private static boolean settingParams(PreparedStatement preparedStatement, Object[] param) throws SQLException {
if (param != null && param.length > 0){
ParameterMetaData parameterMetaData = preparedStatement.getParameterMetaData();
int paramCount = parameterMetaData.getParameterCount();
if (paramCount != param.length){
return false;
}
for (int i = 0; i < paramCount; i++){
preparedStatement.setObject(i+1, param[i]);
}
}
return true;
}
/**
* 更新操作
* @param sql 执行的SQL语句
* @param param 对应的参数列表
* @return
*/
public static boolean update(String sql, Object[] param){
PreparedStatement preparedStatement = null;
Connection connection = getConnection();
try {
preparedStatement = connection.prepareStatement(sql);
if (settingParams(preparedStatement, param) == false){
return false;
}
int result = preparedStatement.executeUpdate();
if (result > 0){
return true;
}
return false;
} catch (SQLException e) {
e.printStackTrace();
}finally {
close(connection, preparedStatement);
}
return false;
}
/**
* 获取单个Bean
* @param sql 执行SQL语句
* @param param 对应的参数列表
* @param clazz 所要获取的对象的类型
* @param 对象的类型
* @return bean
*/
public static T queryForBean(String sql, Object[] param, Class clazz){
Connection connection = getConnection();
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
preparedStatement = connection.prepareStatement(sql);
if (settingParams(preparedStatement, param) == false){
return null;
}
resultSet = preparedStatement.executeQuery();
if (resultSet == null){
return null;
}
if (resultSet.next()){
T data = clazz.newInstance();
ResultSetMetaData resultSetMetaData = resultSet.getMetaData();
int columnCount = resultSetMetaData.getColumnCount();
for (int i = 0; i < columnCount; i++){
String name = resultSetMetaData.getColumnName(i + 1);
Object rData = resultSet.getObject(name);
BeanUtils.copyProperty(data, name, rData);
}
return data;
}else {
return null;
}
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} finally {
close(connection, preparedStatement, resultSet);
}
return null;
}
/**
* 获取Bean并且封装成List
* @param sql 执行SQL语句
* @param param 对应的参数列表
* @param clazz 所要获取的对象的类型
* @param 对象的类型
* @return list
*/
public static List queryForList(String sql, Object[] param, Class clazz){
Connection connection = getConnection();
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
preparedStatement = connection.prepareStatement(sql);
if (settingParams(preparedStatement, param) == false){
return null;
}
resultSet = preparedStatement.executeQuery();
if (resultSet == null){
return null;
}
List results = new ArrayList<>();
while (resultSet.next()){
T data = clazz.newInstance();
ResultSetMetaData resultSetMetaData = resultSet.getMetaData();
int columnCount = resultSetMetaData.getColumnCount();
for (int i = 0; i < columnCount; i++){
String name = resultSetMetaData.getColumnName(i + 1);
Object rData = resultSet.getObject(name);
BeanUtils.copyProperty(data, name, rData);
}
results.add(data);
}
return results;
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} finally {
close(connection, preparedStatement, resultSet);
}
return null;
}
/**
* 关闭connection
* @param connection 连接池对象
*/
private static void close(Connection connection){
if (connection != null){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**
* 关闭Statement
* @param statement
*/
private static void close(Statement statement){
if (statement != null){
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**
* 关闭ResultSet
* @param resultSet
*/
private static void close(ResultSet resultSet){
if (resultSet != null){
try {
resultSet.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
/**
* 关闭Connection 以及Statement
* @param connection
* @param statement
*/
private static void close(Connection connection, Statement statement){
close(connection);
close(statement);
}
/**
* 关闭Connection，Statement以及ResultSet
* @param connection
* @param statement
* @param resultSet
*/
private static void close(Connection connection, Statement statement, ResultSet resultSet){
close(connection, statement);
close(resultSet);
}
}