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field
String 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
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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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