On DBUtils in ThreadLocal

If it is necessary to ensure data security, but also to ensure performance, consider ThreadLocal (thread-local variables)

ThreadLocal: You can create a copy of each thread. Each thread can access its own internal copy.

That is new (created) once, ThreadLocal (copy) multiple times

For example: there is an information CSDN like to sell 100C coins, there are A, B, C three people do not buy a ThreadLocal to buy one, spent a total of 300C coins 

Use the ThreadLocal, A is a buy and to copy and paste the two parts B, C. Took only money 100C

 

For a database, a connection corresponds to a transaction (database is a user-defined sequence of operation, either all these operations do, not to be incomplete.), A transaction may comprise a plurality of DML (Data Manipulation Language) operations.

Transaction process: open a transaction (manual submission will automatically be submitted →) → → various DML normal, just all DML will submit all

                                                                                                                   → failure (abnormal) will just roll back all DML

public class JDBCUtils {
private static ComboPooledDataSource ds = new ComboPooledDataSource();
private static ThreadLocal<Connection> tl=new ThreadLocal<>(); //线程本地变量
	
	/**
	 * 从线程中获取连接
	 * @return
	 * @throws SQLException
	 */
	public static Connection getConnection() throws SQLException {
		//从线程中获取conneciton
		Connection conn = tl.get();  //从tl中获取副本
		if(conn==null){              //如果是第一次从tl里取连接
			conn=ds.getConnection();   //通过数据源获取连接
			//和当前线程绑定
			tl.set(conn);       //给tl中存放一个副本
		}
		return conn;
	}

    // 获取数据源
	public static DataSource getDataSource() {
		return ds;
	}

	// 释放资源
	public static void closeResource( Statement st, ResultSet rs) {
		closeResultSet(rs);
		closeStatement(st);
	}
	
	// 释放资源
	public static void closeResource(Connection conn, Statement st, ResultSet rs) {
		closeResource(st, rs);
		closeConn(conn);
	}

	// 释放 connection
	public static void closeConn(Connection conn) {
		if (conn != null) {
			try {
				conn.close();
				//和线程解绑
				tl.remove();
			} catch (SQLException e) {
				e.printStackTrace();
			}
			conn = null;
		}
	}

	// 释放 statement ctrl + shift + f 格式化代码
	public static void closeStatement(Statement st) {
		if (st != null) {
			try {
				st.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
			st = null;
		}
	}

	// 释放结果集
	public static void closeResultSet(ResultSet rs) {
		if (rs != null) {
			try {
				rs.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
			rs = null;
		}
	}
	
	//开启事务（将自动提交方式 --→ 手动提交方式）
	public static void startTransaction() throws SQLException{
		getConnection().setAutoCommit(false);  //true：自动   false:手动
	}
	
	/**
	 * 事务正常提交,且释放连接
	 */
	public static void commitAndClose(){
		Connection conn = null;
		try {
			conn=getConnection();
			//事务提交
			conn.commit();
			//关闭资源
			conn.close();
			//解除版定
			tl.remove();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
	
	/**
	 * 事务提交失败（异常），回滚且释放资源
	 */
	public static void rollbackAndClose(){
		Connection conn = null;
		try {
			conn=getConnection();
			//事务回滚
			conn.rollback();
			//关闭资源
			conn.close();
			//解除版定
			tl.remove();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
	public static void main(String[] args) throws SQLException {
		//System.out.println(ds.getDataSourceName());
		//System.out.println(ds.getJdbcUrl());
		System.out.println(getConnection());
	}
}

For more information about ThreadLocal can refer to this article  https://blog.csdn.net/qq_23315711/article/details/78642171