【java】对jdbc操作结果简单的映射封装

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【java】对jdbc操作结果简单的映射封装

1. 对jdbc做一个简单的封装，select可以返回一个javabean对象，而不是resultset。主要用了反射。这是我之前写的代码，做了简单的修改。

　　实现功能：a.对数据库的基本操作 增删改查

　　　　　　　b.对查询的单条记录返回一个指定类型的javabean对象，利用java反射，jdbc ResultSet类和ResultSetMetaData类

　　　　　　　c. 对查到的结果集返回一个List， 泛型

　　数据源：用到的 数据库连接池是我自己简单实现的一个连接池：【java】简单实现数据库连接池，主要为了后续实现事务的简单实现

　　用到的java知识 ： 反射，泛型，jdbc

import com.yeyeck.noob.ConnectionPollImpl;
import com.yeyeck.noob.IConnectionPool;import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;public class DBUtil {public static int excuteUpdate(String sql, Object... objects) {IConnectionPool connectionPool = ConnectionPollImpl.getInstance();Connection connection = connectionPool.getConnection();PreparedStatement preparedStatement = null;try {preparedStatement = getStateMent(connection, sql, objects);return preparedStatement.executeUpdate(); //执行sql并返回结果} catch (SQLException e) {e.printStackTrace();} finally {if (preparedStatement != null) {try {preparedStatement.close();} catch (SQLException e) {e.printStackTrace();}}}return 0;}/*** 查询单条记录** @param sql  查询语句* @param clazz 返回对象的class* @param objects 需要的参数，必须跟sql占位符的位置一一对应* @param <T>   泛型返回* @return      返回单个对象*/public static <T> T queryForObject(String sql, Class<T> clazz, Object... objects) {IConnectionPool connectionPool = ConnectionPollImpl.getInstance();Connection connection = connectionPool.getConnection();PreparedStatement preparedStatement = null;ResultSet resultSet = null;T object = null;try {preparedStatement = getStateMent(connection, sql, objects);resultSet = getResultSet(preparedStatement);if (resultSet.next()) {object = invokeObject(resultSet, clazz);}} catch (SQLException | IllegalAccessException | InstantiationException| NoSuchFieldException | NoSuchMethodException | InvocationTargetException e) {e.printStackTrace();} finally {close(preparedStatement, resultSet); //记得关闭
        }return object;}/***查询多条记录** @param sql  查询语句* @param clazz 返回对象的class* @param objects 需要的参数，必须跟sql占位符的位置一一对应* @param <T>   泛型返回** @return list*/public static <T> List<T> queryForList(String sql, Class<T> clazz, Object... objects) {IConnectionPool connectionPool = ConnectionPollImpl.getInstance();Connection connection = connectionPool.getConnection();PreparedStatement preparedStatement = null;ResultSet resultSet = null;List<T> list = new ArrayList<>();try {preparedStatement = getStateMent(connection, sql, objects);resultSet = getResultSet(preparedStatement);while (resultSet.next()) {//调用 invokeObject方法，把一条记录封装成一个对象，添加到list中
                list.add(invokeObject(resultSet, clazz));}} catch (SQLException | IllegalAccessException | InstantiationException| NoSuchFieldException | NoSuchMethodException | InvocationTargetException e) {e.printStackTrace();}  finally {close(preparedStatement, resultSet);}return list.size() > 0 ? list : null;}private static void close(PreparedStatement preparedStatement, ResultSet resultSet) {try {if(resultSet != null) {resultSet.close();}if (preparedStatement != null) {preparedStatement.close();}} catch (SQLException e) {e.printStackTrace();}}/*** 把数据库中的一条记录通过反射包装成相应的Bean* @param resultSet* @param clazz* @param <T>* @return* @throws IllegalAccessException* @throws InstantiationException* @throws SQLException* @throws NoSuchFieldException* @throws NoSuchMethodException* @throws InvocationTargetException*/private static <T> T invokeObject(ResultSet resultSet, Class<T> clazz) throws IllegalAccessException, InstantiationException,SQLException, NoSuchFieldException, NoSuchMethodException, InvocationTargetException {T object = clazz.getDeclaredConstructor().newInstance();ResultSetMetaData metaData = resultSet.getMetaData();for (int i = 0, count = metaData.getColumnCount(); i < count; i++) {String columnName = metaData.getColumnName(i + 1);     //数据库返回结果的列名String fieldName = StringUtil.camelName(columnName); //去掉列名中的下划线“_”并转为驼峰命名Field field = clazz.getDeclaredField(fieldName);            //根据字段名获取fieldString methName = setMethodName(fieldName);         //拼set方法名Class type = field.getType();                       //获取字段类型Method setMethod = clazz.getDeclaredMethod(methName, field.getType());Object value = resultSet.getObject(i + 1);            //获取字段值setMethod.invoke(object, type.cast(value));       //强转并且赋值
        }return object;}private static PreparedStatement getStateMent(Connection connection, String sql, Object... objects) throws SQLException {PreparedStatement preparedStatement = connection.prepareStatement(sql);for (int i = 0, len = objects.length; i < len; i++) {preparedStatement.setObject(i + 1, objects[i]);  //给sql每个？占位符填上数据
        }return preparedStatement;}private static ResultSet getResultSet(PreparedStatement statement) throws SQLException {if (statement == null) {return null;} else {return statement.executeQuery();}}private static String setMethodName(String str) {return "set" + StringUtil.firstUpperCase(str);}
}

其中用到的StringUtil的几个方法

public class StringUtil {/*** 转为驼峰命名* @param str* @return string*/public static String camelName(String str) {if (!isEmpty(str)) {StringBuilder stringBuilder = new StringBuilder();for (int i = 0, len = str.length(); i < len; i++) {if (str.charAt(i) == '_') {while (str.charAt(i + 1) == '_') {i++;}stringBuilder.append(("" + str.charAt(++i)).toUpperCase());} else {stringBuilder.append(str.charAt(i));}}return stringBuilder.toString();}return str;}/*** 判断是否为空串** @param str* @return*/public static boolean isBlank(String str) {if (str != null && str.length() > 0) {for (int i = 0, len = str.length(); i < len; i++) {if (!Character.isSpaceChar(str.charAt(i))) {return false;}}}return true;}/*** 判断是否为空串 ？！！！ 我怎么又写了个一样的方法？！！！* @param str* @return*/public static boolean isEmpty(String str) {return str == null || str.length() == 0;}/*** 将第一个字母替换为大写* @param str* @return*/public static String firstUpperCase(String str) {return str.substring(0, 1).toUpperCase() + str.substring(1, str.length());}
}

测试

1.测试用到的表

 CREATE TABLE `t_user` (`id` int(11) NOT NULL AUTO_INCREMENT,`username` varchar(50) DEFAULT NULL,`age` int(11) NOT NULL,PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8 |

初始数据

测试代码

import java.util.List;public class DBUtilTest {public static void main(String[] args) {List<User> users1 = DBUtil.queryForList("select * from t_user", User.class);System.out.println(users1);User user = new User();user.setUsername("刘能");user.setAge(12);String sql1 = "insert into `t_user`(username, age) values (?, ?)";System.out.println("insert 语句测试返回结果：" + DBUtil.excuteUpdate(sql1, user.getUsername(), user.getAge()));List<User> users2 = DBUtil.queryForList("select * from t_user", User.class);System.out.println(users2);String sql2 = "delete from t_user where id = ?";System.out.println("delete 语句测试返回结果：" + DBUtil.excuteUpdate(sql2, 3));String sql3 = "update t_user set age = ? where id = ?";System.out.println("update 语句测试返回结果：" + DBUtil.excuteUpdate(sql3, 100, 1));String sql4 = "select * from t_user where id = ?";User user2 = DBUtil.queryForObject(sql4, User.class, 2);System.out.println("select 语句测试返回结果: " + user2 );List<User> users3 = DBUtil.queryForList("select * from t_user", User.class);System.out.println(users3);}}

测试结果

[User{id=1, username='小明', age=100}, User{id=2, username='小红', age=15}, User{id=4, username='小二', age=12}, User{id=5, username='刘能', age=12}]
insert 语句测试返回结果：1
[User{id=1, username='小明', age=100}, User{id=2, username='小红', age=15}, User{id=4, username='小二', age=12}, User{id=5, username='刘能', age=12}, User{id=6, username='二蛋', age=99}]
delete 语句测试返回结果：1
update 语句测试返回结果：1
select 语句测试返回结果: User{id=2, username='小红', age=15}
[User{id=1, username='小明', age=20}, User{id=2, username='小红', age=15}, User{id=4, username='小二', age=12}, User{id=6, username='二蛋', age=99}]

数据库数据

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