使用ThreadLocal搭建支持并发,事务的DAO

以你之姓@ 2022-05-11 03:48 167阅读 0赞

ThreadLocal的原理是使用一个hashMap保存connection,而键为当前线程即`Thread.currentThread()`  
下面先简单模拟一个ThreadLocal

public class MyThreadLocal <T> { private Map<Thread, T> map = new HashMap<Thread, T>(); public void set(T data) { // 使用当前线程做key map.put(Thread.currentThread(), data); } public T get() { return map.get(Thread.currentThread()); } public void remove() { map.remove(Thread.currentThread()); } }

写一个支持事务的dao,需要提供getconnection(),beginTransaction(),commitTransaction(),rollBackTransaction()的方法

使用该getTXConnection()调包之前DAO的CRUD 的getConnection()方法,并把connection 存放到ThreadLocal中

public static Connection getTXConnection(){ Connection connection = tl.get(); if (connection==null){ try { connection = dataSource.getConnection(); } catch (SQLException e) { e.printStackTrace(); } tl.set(connection); } return connection; }

beginTransaction开启事务

public static void beginTransaction() { Connection con = tl.get(); if (con==null){ try { con = dataSource.getConnection(); con.setAutoCommit(false); } catch (SQLException e) { e.printStackTrace(); } tl.set(con); }else{ throw new RuntimeException("你已经开启事务了"); } }

commitTransaction提交事务,关闭连接,移除ThreadLocal中的connection

public static void commitTransaction(){ Connection con = tl.get(); if (con==null){ throw new RuntimeException("你还没有开启事务"); }else { try { con.commit(); con.close(); tl.remove(); } catch (SQLException e) { e.printStackTrace(); } } }

rollBackTransaction回滚事务,关闭连接,移除ThreadLocal中的connection

public static void rollBackTransaction() { Connection con = tl.get(); if (con==null){ throw new RuntimeException("你还没有开启事务"); }else { try { con.rollback(); con.close(); tl.remove(); } catch (SQLException e) { e.printStackTrace(); } } }

对于close方法,对于事务而言,是不需要关闭的,关闭在commitTransaction和rollBackTransaction中,但为了兼容没有开启事务的CRUD,这里需要判断

public static void close(Connection con, PreparedStatement ps) { if (ps != null) { try { ps.close(); } catch (SQLException e) { e.printStackTrace(); } } Connection connection = tl.get(); //不是事务connection if (connection==null){ try { con.close(); } catch (SQLException e) { e.printStackTrace(); } }else { //也不是事务connection if (con!=connection){ try { con.close(); } catch (SQLException e) { e.printStackTrace(); } } } }

接下来是加强之前写的DAO了,这里只展示update方法

public class JDBCUtils { private static BasicDataSource dataSource; private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>(); static { dataSource = new BasicDataSource(); Properties properties = new Properties(); InputStream in = JDBCUtils.class.getClassLoader().getResourceAsStream("jdbc.properties"); try { properties.load(in); dataSource.setDriverClassName(properties.getProperty("driver")); dataSource.setUrl(properties.getProperty("jdbcUrl")); dataSource.setUsername(properties.getProperty("user")); dataSource.setPassword(properties.getProperty("password")); } catch (IOException e) { e.printStackTrace(); } } //insert update delete public static void update(String sql,Object... args){ Connection connection = getTXConnection(); PreparedStatement ps=null; try { ps = connection.prepareStatement(sql,Statement); for (int i=0;i<args.length;i++){ ps.setObject(i+1,args[i]); } ps.executeUpdate(); }catch (Exception e){ e.printStackTrace(); } JDBCUtils.close(connection,ps); } }