数据库访问 BaseDao的封装
作者：互联网
package com.fengmy.javaweb02.base;
import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.pool.DruidDataSourceFactory;
import javax.sql.DataSource;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.Properties;
/**
* 数据库连接工具类
*
* @since 2022/3/11
*/
public abstract class BaseDao<T> {
public final String DRIVER = "com.mysql.cj.jdbc.Driver";
public final String URL = "jdbc:mysql://localhost:3306/fruitdb?useUnicode=true&useCharacterEncoding=utf-8";
public final String USER = "root";
public final String PWD = "root";
protected Connection conn;
protected PreparedStatement psmt;
protected ResultSet res;
// T 的Class对象
private Class entityClass;
public BaseDao() {
Type genericSuperclass = getClass().getGenericSuperclass();
Type[] actualTypeArguments = ((ParameterizedType) genericSuperclass).getActualTypeArguments();
Type actualType = actualTypeArguments[0];
System.out.println(actualType.getTypeName());
try {
entityClass = Class.forName(actualType.getTypeName());
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
/**
* 获取数据库连接
*
* @return 数据库连接
*/
protected Connection getConn() {
try {
DruidDataSource dds=new DruidDataSource();
dds.setDriverClassName(DRIVER);
dds.setUrl(URL);
dds.setUsername(USER);
dds.setPassword(PWD);
dds.setInitialSize(5);
dds.setMaxActive(10);
dds.setMaxActive(3000);
conn=dds.getConnection();
return conn;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 释放资源
*
* @param res 数据集
* @param psmt 预处理
* @param conn 数据库连接
*/
protected void close(ResultSet res, PreparedStatement psmt, Connection conn) {
try {
if (res != null) {
res.close();
}
if (psmt != null) {
psmt.close();
}
if (conn != null && !conn.isClosed()) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
/**
* 对数据库更新操作的抽取
*
* @param sql sql语句
* @param params 预处理数据参数
* @return 返回受影响行数
*/
protected int executeUpdate(String sql, Object... params) {
boolean insertFlag = false;
insertFlag = sql.trim().toUpperCase(Locale.ROOT).startsWith("INSERT");
try {
conn = getConn();
if (insertFlag) {
psmt = conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS);
} else {
psmt = conn.prepareStatement(sql);
}
setParams(psmt, params);
int count = psmt.executeUpdate();
if (insertFlag) {
res = psmt.getGeneratedKeys();
if (res.next()) {
return ((Long) res.getLong(1)).intValue();
}
}
return count;
} catch (SQLException e) {
e.printStackTrace();
} finally {
close(res, psmt, conn);
}
return 0;
}
/**
* 设置预处理参数
*/
private void setParams(PreparedStatement psmt, Object... params) throws SQLException {
if (params != null && params.length > 0) {
for (int i = 0; i < params.length; i++) {
psmt.setObject(i + 1, params[i]);
}
}
}
/**
* 通过反射技术给object对象的属性赋值
*/
private void setValue(Object obj, String property, Object propertyValue) {
Class clazz = obj.getClass();
try {
Field field = clazz.getDeclaredField(property);
if (field != null) {
field.setAccessible(true);
field.set(obj, propertyValue);
}
} catch (NoSuchFieldException | IllegalAccessException e) {
e.printStackTrace();
}
}
/**
* 对数据库查询操作的抽取
*
* @param sql sql语句
* @param params 预处理数据参数
* @return 返回T类型数据列表
*/
protected List<T> executeQuery(String sql, Object... params) {
List<T> list = new ArrayList<>();
try {
conn = getConn();
psmt = conn.prepareStatement(sql);
setParams(psmt, params);
ResultSet res = psmt.executeQuery();
ResultSetMetaData rsmd = res.getMetaData();
int columnCount = rsmd.getColumnCount();
while (res.next()) {
T entity = getT(columnCount, rsmd, res);
list.add(entity);
}
} catch (SQLException | IllegalAccessException | InstantiationException e) {
e.printStackTrace();
} finally {
close(res, psmt, conn);
}
return list;
}
/**
* 获取T对象
*
* @param columnCount 列数量
* @param rsmd 元数据
* @param res 数据集
* @return T类型
* @throws InstantiationException 异常
* @throws IllegalAccessException 异常
* @throws SQLException 异常
*/
private T getT(int columnCount, ResultSetMetaData rsmd, ResultSet res) throws InstantiationException, IllegalAccessException, SQLException {
if (entityClass != null) {
T entity = (T) entityClass.newInstance();
for (int i = 0; i < columnCount; i++) {
String columnName = rsmd.getColumnName(i + 1);
Object columnValue = res.getObject(i + 1);
setValue(entity, columnName, columnValue);
}
return entity;
}
return null;
}
/**
* 对数据库查询操作的抽取
*
* @param sql sql语句
* @param params 预处理数据参数
* @return 返回T类型
*/
protected T load(String sql, Object... params) {
try {
conn = getConn();
psmt = conn.prepareStatement(sql);
setParams(psmt, params);
ResultSet res = psmt.executeQuery();
ResultSetMetaData rsmd = res.getMetaData();
int columnCount = rsmd.getColumnCount();
if (res.next()) {
return getT(columnCount, rsmd, res);
}
} catch (SQLException | IllegalAccessException | InstantiationException e) {
e.printStackTrace();
} finally {
close(res, psmt, conn);
}
return null;
}
/**
* 对数据库复杂查询操作的抽取
*
* @param sql sql语句
* @param params 预处理数据参数
* @return 返回T类型
*/
protected Object[] executeComplexQuery(String sql, Object... params) {
try {
conn = getConn();
psmt = conn.prepareStatement(sql);
setParams(psmt, params);
ResultSet res = psmt.executeQuery();
ResultSetMetaData rsmd = res.getMetaData();
int columnCount = rsmd.getColumnCount();
Object[] columnValueArr = new Object[columnCount];
if (res.next()) {
for (int i = 0; i < columnCount; i++) {
Object columnValue = res.getObject(i + 1);
columnValueArr[i] = columnValue;
}
return columnValueArr;
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
close(res, psmt, conn);
}
return null;
}
}
标签：封装,res,数据库,BaseDao,params,sql,return,psmt,conn 来源： https://www.cnblogs.com/jeremie00/p/16029874.html