从mysql获取数据方法的封装
获取连接对象的封装
package com.qf.common;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
/***
* 数据库管理类，负责创建连接和关闭资源
*
* @author Administrator
*
*/
public class DBManager {
public static String jdbcDriver = "com.mysql.jdbc.Driver";
public static String jdbcUrl = "jdbc:mysql:///shop";
public static String username = "root";
public static String password = "123";
// 得到连接对象
public static Connection getConnection() {
try {
Class.forName(jdbcDriver);
return DriverManager.getConnection(jdbcUrl, username, password);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
// 关闭资源
public static void closeAll(AutoCloseable... autoCloseables) {
for (AutoCloseable autoCloseable : autoCloseables) {
if (autoCloseable != null) {
try {
autoCloseable.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
}
在Dao层对数据库增删改查方法的封装
/***
* 放一些公共的增删改查方法
*
* @author Administrator
*
*/
public class DBUtil<T> {
private static Connection connection = null;
private static PreparedStatement ps = null;
private ResultSet rs = null;
private ResultSetMetaData metaData;
/**
* 增删改操作
*
* @return
*/
public static int commonOper(String sql, Object... param) {
// select * from t_user where id = ? and username = ?
// User
try {
// 得到一个连接对象
connection = DBManager.getConnection();
// 开启事务
connection.setAutoCommit(false);
// 得到一个执行对象
ps = connection.prepareStatement(sql);
// 给sql语句的参数赋值
for (int i = 0; i < param.length; i++) {
ps.setObject(i + 1, param[i]);
}
// 执行增删改操作
int result = ps.executeUpdate();
// 提交事务
connection.commit();
System.out.println("执行成功！受影响的行数-->" + result);
return result;
} catch (Exception e) {
e.printStackTrace();
if (connection != null) {
try {
// 回滚
connection.rollback();
connection.setAutoCommit(true);
} catch (SQLException e1) {
e1.printStackTrace();
}
}
} finally {
// 关闭资源
DBManager.closeAll(ps, connection);
}
return -1;
}
/***
* 查询集合数据
*
* @param sql
* @param clazz
* @param param
* @return
*/
public List getList(String sql, Class clazz, Object... param) {
List list = new ArrayList<>();
try {
connection = DBManager.getConnection();
ps = connection.prepareStatement(sql);
for (int i = 0; i < param.length; i++) {
ps.setObject(i + 1, param[i]);
}
rs = ps.executeQuery();
// 得到ResultSetMetaData对象，这个对象包括列的信息(列的名称和类型等等)
metaData = rs.getMetaData();
// 得到结果集中列的个数
int columnCount = metaData.getColumnCount();
while (rs.next()) {
T ins = clazz.newInstance();
for (int i = 1; i <= columnCount; i++) {
// 得到列名
String name = metaData.getColumnName(i);
Object value = rs.getObject(i);
Field field = clazz.getDeclaredField(name);
field.setAccessible(true);
// user.setUsername(name)
field.set(ins, value);
}
list.add(ins);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
DBManager.closeAll(rs, ps, connection);
}
return list;
}
/**
* 得到单个对象
*
* @param sql
* @param clazz
* @param param
* @return
*/
public T getSingleInstace(String sql, Class clazz, Object... param) {
try {
connection = DBManager.getConnection();
ps = connection.prepareStatement(sql);
for (int i = 0; i < param.length; i++) {
ps.setObject(i + 1, param[i]);
}
rs = ps.executeQuery();
metaData = rs.getMetaData();
int columnCount = metaData.getColumnCount();
if (rs.next()) {
T ins = clazz.newInstance();
for (int i = 1; i <= columnCount; i++) {
// 得到列名
String columnName = metaData.getColumnName(i);
// 得到列名对应的数据
Object value = rs.getObject(i);
Field field = clazz.getDeclaredField(columnName);
field.setAccessible(true);
field.set(ins, value);
}
return ins;
}
} catch (Exception e) {
e.printStackTrace();
} finally {
DBManager.closeAll(rs, ps, connection);
}
return null;
}
/**
* 查询条数
* @return
*/
public int getCount(String sql,Object...param){
int count = 0;
try {
connection = DBManager.getConnection();
ps = connection.prepareStatement(sql);
for (int i = 0; i < param.length; i++) {
ps.setObject(i + 1, param[i]);
}
rs = ps.executeQuery();
if(rs.next()){
count = rs.getInt(1);
}
}catch(Exception e){
e.printStackTrace();
}finally {
DBManager.closeAll(rs,ps,connection);
}
return count;
}
/**
* 获取id
* @return
*/
public int getId(String sql,Object...param){
int id = 0;
try {
connection = DBManager.getConnection();
ps = connection.prepareStatement(sql);
for (int i = 0; i < param.length; i++) {
ps.setObject(i + 1, param[i]);
}
rs = ps.executeQuery();
if(rs.next()){
id = rs.getInt(1);
}
}catch(Exception e){
e.printStackTrace();
}finally {
DBManager.closeAll(rs,ps,connection);
}
return id;
}
/**
* 获取map数据
*/
public Map> getOrderDetailList(String sql, Class clazz, Object... param) {
Map> map = new HashMap<>();
try {
connection = DBManager.getConnection();
ps = connection.prepareStatement(sql);
for (int i = 0; i < param.length; i++) {
ps.setObject(i + 1, param[i]);
}
rs = ps.executeQuery();
// 得到ResultSetMetaData对象，这个对象包括列的信息(列的名称和类型等等)
metaData = rs.getMetaData();
// 得到结果集中列的个数
int columnCount = metaData.getColumnCount();
while (rs.next()) {
Order order = new Order();
order.setId(rs.getInt("id"));
order.setO_orderdate(rs.getDate("o_orderdate"));
T ins = clazz.newInstance();
for (int i = 1; i <= columnCount; i++) {
// 得到列名
String name = metaData.getColumnName(i);
Object value = rs.getObject(i);
try {
Field field = clazz.getDeclaredField(name);
field.setAccessible(true);
// user.setUsername(name)
field.set(ins, value);
} catch (NoSuchFieldException e) {
System.out.println(name+"此字段不存在！");
} catch (IllegalArgumentException e) {
System.out.println(name+"此字段类型不匹配");
}
}
List list = map.get(order);
if(list==null){
list = new ArrayList<>();
}
//把订单详情对象添加到集合中
list.add(ins);
map.put(order, list);
}
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} finally {
DBManager.closeAll(rs, ps, connection);
}
return map;
}
}