Question

我有这段Java代码，我尝试遍历记录，意味着我想从第一个记录跳到最后一个记录，反之亦然。你可以看到'n'在记录中向前迭代，'p'向后迭代。一旦我到达最后一条记录/第一条记录，就会抛出异常。我该如何解决这个问题？

谢谢你的帮助： - ）

public void NavigateTable() {
    try {
        statement = dbconnect.connect.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY);
        rs = statement.executeQuery("SELECT * FROM author");
        char selection;
        rs.beforeFirst();
        do {
            System.out.println("(n)ext data, (p)revious data or (e)xit.");
            selection = readChar("");
            if (selection == 'n') {
                rs.next();
                System.out.print("AuthorID: " + rs.getInt("authorid"));
                System.out.print("\tFirst name: " + rs.getString("firstname"));
                System.out.print("\tLast name: " + rs.getString("lastname"));
                System.out.print("\tPublisherID: " +rs.getInt("publisherid")); 
                System.out.println();      
            } else if (selection == 'p') {
                rs.previous();
                System.out.print("AuthorID: " + rs.getInt("authorid"));
                System.out.print("\tFirst name: " + rs.getString("firstname"));
                System.out.print("\tLast name: " + rs.getString("lastname"));
                System.out.print("\tPublisherID: " +rs.getInt("publisherid")); 
                System.out.println();   
            }

        } while (selection != 'e'); 
    }
    catch (Exception e) {
        System.out.println("Exception " + e.getMessage());
    }

}

Answer 1

你应该立即阅读所有记录，并将它们放在像ArrayList这样的地方，你可以轻松地从头到尾跳转，反之亦然。这也允许您释放数据库资源，这是一件好事。

Answer 2

你盲目地滚动ResultSet的两端。您需要使用isFirst()和isLast()方法检查您是在开始还是结束，然后避免在这些情况下调用next()或previous()。

Answer 3

通常，您不希望在用户与系统交互时打开ResultSet（即，从用户读取输入以确定是向前还是向后）。

话虽这么说，为了解决你的问题，你可以尝试这样的事情：

public void NavigateTable() {
    try {
        statement = dbconnect.connect.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY);
        rs = statement.executeQuery("SELECT * FROM author");
        char selection;
        rs.beforeFirst();
        do {
            System.out.println("(n)ext data, (p)revious data or (e)xit.");
            selection = readChar("");
            if (selection == 'n') {
                if (rs.isLast()) rs.beforeFirst();
                else rs.next();
                System.out.print("AuthorID: " + rs.getInt("authorid"));
                System.out.print("\tFirst name: " + rs.getString("firstname"));
                System.out.print("\tLast name: " + rs.getString("lastname"));
                System.out.print("\tPublisherID: " +rs.getInt("publisherid")); 
                System.out.println();      
            } else if (selection == 'p') {
                if (rs.isFirst()) rs.afterLast();
                else rs.previous();
                System.out.print("AuthorID: " + rs.getInt("authorid"));
                System.out.print("\tFirst name: " + rs.getString("firstname"));
                System.out.print("\tLast name: " + rs.getString("lastname"));
                System.out.print("\tPublisherID: " +rs.getInt("publisherid")); 
                System.out.println();

            }

如何从我的数据库中的第一条记录跳转到最后一条记录

3 个答案: