回滾的意義---JDBC事務回滾探究

JDBC手動事務提交回滾的常見寫法一直是rollback寫在commit的catch之后:

try{
 conn.setAutoCommit(false);
　　ps.executeUpdate();

　　ps.executeUpdate();

　　conn.commit();

}catch(Exception e){
 conn.rollback();  
}

但是,這種回滾是沒有意義的:

一旦commit前出錯,　　就不提交了,　　回滾無用

一旦commit了,　　　　說明沒錯,　　　不用回滾

找到一篇和我觀點相同的文章:

<JDBC 事務的回滾 提交>

我以為無需回滾,即使真要回滾,需要將commit寫在主要業務的try...catch之后,一旦主要業務中途出錯,回滾.

表:JDBC事務3種寫法回滾比較

import java.sql.*;

public class TestJDBC {

    public static final String URL = "jdbc:mysql://127.0.0.1/test";
    public static final String USER_NAME = "root";
    public static final String USER_PWD = "root";

    private static Connection conn = null;
    private static PreparedStatement ps;

    private static void connOpen() throws SQLException {
        conn = DriverManager.getConnection(URL, USER_NAME, USER_PWD);
    }

    private static void connClose() throws SQLException {
        if (ps != null) {
            ps.close();
            ps = null;
        }
        if (conn != null) {
            conn.close();
            conn = null;
        }
    }

    private static void testRollBack() throws SQLException {
        connOpen();
        try {

  conn.setAutoCommit(false);

            String strSQL = "INSERT INTO customer(uname,pwd) VALUES(?,'1')";
            ps = conn.prepareStatement(strSQL);

            // 插入一條數據
            ps.setString(1, "悟空");
            ps.executeUpdate();

            // 出異常
            if (true) {
                throw new SQLException();
            }

            // 再插入一條數據
            ps.setString(1, "八戒");
            ps.executeUpdate();

            // conn.commit();
        } catch (Exception e) {
            System.out.println("異常!");
            try {
                conn.rollback();
            } catch (SQLException e1) {
                e1.printStackTrace();
            }
        }
        try {
    conn.commit();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        connClose();

    }

    private static void selectAll() throws SQLException {
        connOpen();
        ps = conn.prepareStatement("select * from customer");
        ResultSet rs = ps.executeQuery();
        while (rs.next()) {
            System.out.print(rs.getString(2) + " : ");
            System.out.println(rs.getString(1));
        }
        connClose();
    }

    public static void main(String[] args) throws SQLException {
        testRollBack();
        selectAll();
    }
}