jdbc连接数据库工具类

import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class DBUtils {

// 表示定义数据库的用户名
private static String USERNAME = "root";
// 定义数据库的密码
private static String PASSWORD = "root";
// 定义数据库的驱动信息
private static String DRIVER = "com.mysql.jdbc.Driver";
// 定义访问数据库的地址
private static String URL = "jdbc:mysql://localhost:3306/db";

private static DBUtils per = null;
// 定义数据库的链接
private Connection con = null;
// 定义sql语句的执行对象
private PreparedStatement pstmt = null;
// 定义查询返回的结果集合
private ResultSet resultSet = null;

private DBUtils() {

}

/**
* 单例模式，获得工具类的一个对象
*
* @return
*/
public static DBUtils getInstance() {
if (per == null) {
per = new DBUtils();
per.registeredDriver();
}
return per;
}

private void registeredDriver() {
// TODO Auto-generated method stub
try {
Class.forName(DRIVER);
System.out.println("注册驱动成功！");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

/**
* 获得数据库的连接
*
* @return
*/
public Connection getConnection() {
try {
con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("连接数据库成功!!");
return con;
}

/**
* 完成对数据库的表的添加删除和修改的操作
*
* @param sql
* @param params
* @return
* @throws SQLException
*/
public boolean executeUpdate(String sql, List<Object> params)
throws SQLException {

boolean flag = false;

int result = -1;  // 表示当用户执行添加删除和修改的时候所影响数据库的行数

pstmt = con.prepareStatement(sql);

if (params != null && !params.isEmpty()) {
int index = 1;
for (int i = 0; i < params.size(); i++) {
pstmt.setObject(index++, i);
}
}

result = pstmt.executeUpdate();
flag = result > 0 ? true : false;

return flag;
}

/**
* 从数据库中查询数据
*
* @param sql
* @param params
* @return
* @throws SQLException
*/
public List<Map<String, Object>> executeQuery(String sql,
List<Object> params) throws SQLException {
List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
int index = 1;
pstmt = con.prepareStatement(sql);
if (params != null && !params.isEmpty()) {
for (int i = 0; i < params.size(); i++) {
pstmt.setObject(index++, params.get(i));
}
}
resultSet = pstmt.executeQuery();
ResultSetMetaData metaData = resultSet.getMetaData();
int cols_len = metaData.getColumnCount();
while (resultSet.next()) {
Map<String, Object> map = new HashMap<String, Object>();
for (int i = 0; i < cols_len; i++) {
String cols_name = metaData.getColumnName(i + 1);
Object cols_value = resultSet.getObject(cols_name);
if (cols_value == null) {
cols_value = "";
}
map.put(cols_name, cols_value);
}
list.add(map);
}
return list;

}

/**
* jdbc的封装可以用反射机制来封装,把从数据库中获取的数据封装到一个类的对象里
*
* @param sql
* @param params
* @param cls
* @return
* @throws Exception
*/
public <T> List<T> executeQueryByRef(String sql, List<Object> params,
Class<T> cls) throws Exception {
List<T> list = new ArrayList<T>();
int index = 1;
pstmt = con.prepareStatement(sql);
if (params != null && !params.isEmpty()) {
for (int i = 0; i < params.size(); i++) {
pstmt.setObject(index++, params.get(i));
}
}
resultSet = pstmt.executeQuery();
ResultSetMetaData metaData = resultSet.getMetaData();
int cols_len = metaData.getColumnCount();
while (resultSet.next()) {
T resultObject = cls.newInstance();  // 通过反射机制创建实例
for (int i = 0; i < cols_len; i++) {
String cols_name = metaData.getColumnName(i + 1);
Object cols_value = resultSet.getObject(cols_name);
if (cols_value == null) {
cols_value = "";
}
Field field = cls.getDeclaredField(cols_name);
field.setAccessible(true); // 打开javabean的访问private权限
field.set(resultObject, cols_value);
}
list.add(resultObject);
}
return list;

}

public void closeDB() {
if (resultSet != null) {
try {
resultSet.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (pstmt != null) {
try {
pstmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (con != null) {
try {
con.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

}

import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class Test {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub

DBUtils db = DBUtils.getInstance();
db.getConnection();
String sql = "SELECT name,introduction,location FROM activity WHERE id IN(SELECT activityId from mem_act_collect where memberId = ?)";
List<Activity> reslist = new ArrayList<Activity>();
List<Object> list = new ArrayList<Object>();
list.add(2014303342);

try {
reslist = db.executeQueryByRef(sql,list,Activity.class);

for(Activity ac:reslist){
System.out.println(ac.toString());
}

} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
db.closeDB();
}

}

}