依赖：

 <!-- 连接MySQL数据库的依赖，其他数据库网上找pom依赖替换 --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.15</version></dependency><!-- 阿里巴巴连接池 --><dependency><groupId>com.alibaba</groupId><artifactId>druid</artifactId><version>1.1.21</version></dependency>

DBUntil（工具类）

public class DBUntil {private static String  url;private static String name;private static String password;private   String drive;private   Connection connection;private  Statement statement;private static DruidDataSource dds;private static int minPool =10;//最小连接数private static int maxPool =20;//最大连接数private static DBUntil DB ;public static void initPool() {dds = new DruidDataSource();dds.setUrl(url);dds.setUsername(name);dds.setPassword(password);dds.setInitialSize(minPool);dds.setMaxActive(maxPool);}public Statement createStatements() {try {//Class.forName(drive);connection = dds.getConnection();statement = connection.createStatement();} catch (SQLException e) {throw new RuntimeException(e);}return statement;}public PreparedStatement preparedStatement(String sql){try {return connection.prepareStatement(sql);} catch (SQLException e) {throw new RuntimeException(e);}}public void close()  {dds.close();}/*访问器*/public void setUrl(String url) {this.url = url;}public void setName(String name) {this.name = name;}public void setPassword(String password) {this.password = password;}public void setDrive(String drive) {this.drive = drive;}public void setMinPool(int minPool) {this.minPool = minPool;}public void setMaxPool(int maxPool) {this.maxPool = maxPool;}public static DBUntil getDB() {DB = new DBUntil();return DB;}
}

使用：

private static DBUntil db = DBUntil.getDB();
private static Statement statement;
private  String sql;
private PreparedStatement ps;//预编译static {db.setUrl("");//数据库url（jdbc:mysql://url:端口/数据库名称?characterEncoding=utf8&useSSL=false&serverTimezone=Asia/Shanghai&rewriteBatchedStatements=true）db.setName("");//用户名db.setPassword("");//密码db.initPool();//初始化连接池/*设置连接数数db.setMinPool();db.setMaxPool();*///statement = db.createStatements();}//初始化/*在方法中调用 查询为例*/
sql ="SELECT * FROM userinfo WHERE userinfo.username=? AND userinfo.password=?";try {ps= db.preparedStatement(sql);ps.setString(1,username);//将username替代sql第一个问号ps.setString(2,password);//将username替代sql第二个问号ResultSet rs= ps.executeQuery();//增删该ps.executeUpdate()
}