MySql 的连接 关闭等

package com.zx.util;
    import java.sql.*;
    import java.util.*;

public class MySql {
private static String url = "jdbc:mysql://localhost:3306/library2";
    private static String user = "root";
private static String password = "199212";

private MySql() {
}

static {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

public static Connection getCon() {
try {
return DriverManager.getConnection(url, user, password);
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}

public static void free(ResultSet re, Statement stat, Connection con) {
try {
if (re != null)
re.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
if (stat != null)
stat.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
if (con != null)
con.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
//读数据库，返回int 型
public static int readD(String sql, Object[] params) {
Connection con = null;
PreparedStatement ps = null;
ResultSet re = null;
int rows = 0;

try {

con = Tool.getCon();
ps = (PreparedStatement) con.prepareStatement(sql);
if (params != null) {
for (int i = 0; i < params.length; i++) {
ps.setObject(i + 1, params[i]);
}
}
re = ps.executeQuery();
ResultSetMetaData rsmd = (ResultSetMetaData) re.getMetaData();
int count = rsmd.getColumnCount();

while (re.next()) {
                rows++;
}
} catch (SQLException e) {

e.printStackTrace();
} finally {
Tool.free(re, ps, con);
}

return rows;

}

public int writeDB(String sql) {
return writeDB(sql, null);
}
//写数据库方法
public static int writeDB(String sql, Object[] params) {
Connection con = null;
PreparedStatement ps = null;
ResultSet re = null;

int row = 0;

try {
con = MySql.getCon();
ps = (PreparedStatement) con.prepareStatement(sql);
if (params != null) {
for (int i = 0; i < params.length; i++) {
ps.setObject(i + 1, params[i]);
}
}
row = ps.executeUpdate();
} catch (SQLException e) {
e.printStackTrace();
} finally {
MySql.free(re, ps, con);
}
return row;
}
//读数据库方法
public static List<Map<String, Object>> readDB(String sql, Object[] params) {
Connection con = null;
PreparedStatement ps = null;
ResultSet rs = null;
ArrayList<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
// map<>里，string 是键，就是列名，object是值，是集合，一个map得到一行记录

try {
con = Tool.getCon();
ps = con.prepareStatement(sql);

// sql语句参数化
if (params != null) {
for (int i = 0; i < params.length; i++) {
ps.setObject(i + 1, params[i]);
}
}
rs = ps.executeQuery();
ResultSetMetaData rsmd = rs.getMetaData();
int count = rsmd.getColumnCount();// 一共获得几列
String[] columName = new String[count];
for (int i = 0; i < count; i++) {

columName[i] = rsmd.getColumnName(i + 1);// 获得列名
}
while (rs.next()) {
HashMap<String, Object> map = new HashMap<String, Object>();
for (int i = 0; i < count; i++) {
map.put(columName[i], rs.getObject(i + 1));

}
list.add(map);
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
Tool.free(rs, ps, con);
}
return list;
}

}