事务--保存点

快来打我* 2022-08-09 01:48 68阅读 0赞

再上一个例子中，事务如果发生回滚，会将整个事务全部撤销，如果不想全部撤销，而是只撤销其中的一部分，可以使用保存点(Savepoint)

package cn.itcast.jdbc;
    
    import java.sql.Connection;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Savepoint;
    import java.sql.Statement;
    
    public class SavePointTest { 
    
        public static void main(String[] args) throws SQLException {
            test();
        }
    
        static void test() throws SQLException {
            Connection conn = null;
            Statement st = null;
            ResultSet rs = null;
            Savepoint sp = null;
    
            try {
                conn = JdbcUtils.getConnection();
                conn.setAutoCommit(false); // 关闭自动提交
    
                st = conn.createStatement();
                String sql = "update user set money =money-10 where id=1";
                st.executeUpdate(sql);
    
                sql = "update user set money =money-10 where id=3";
                st.executeUpdate(sql);
    
                sp = conn.setSavepoint(); // 设置保存点
    
                sql = "select money from user where id=2";
                rs = st.executeQuery(sql);
                float money = 0.0f;
                if (rs.next())
                    money = rs.getFloat(1);
                if (money > 300)
                    throw new RuntimeException("超过最大值");
    
                sql = "update user set money =money+10 where id=2";
                st.executeUpdate(sql);
    
                conn.commit(); // 提交
            } catch (RuntimeException e) {
                if (conn != null && sp != null) {
                    conn.rollback(sp); // 出现异常，回滚到sp
                    conn.commit();
                }
                throw e;
            } catch (SQLException e) {
                if (conn != null)
                    conn.rollback(); // 出现异常，回滚
                throw e;
            } finally {
                JdbcUtils.free(rs, st, conn);
            }
        }
    }

在这个例子中如果发生了异常，那么id=1和id=2的操作不会被撤销，事务只回滚到Savepoint的位置。