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基本上，我的 Web 应用程序中有两个类，一个类“FormProcess.java”，它将信息插入 HTML 表单，执行一些计算，然后将结果输出为 HTML。这绝对没问题。

我还有一个用于将数据添加到 MySQL 数据库的新行中的类，该类称为“SqlConnect.java”。如果我在服务器上单独运行它（即它正确地在表上插入一行），这也可以正常工作。

我正在努力使 SqlConnect 方法从 FormProcess 类运行。当我将以下内容添加到 FormProcess 时：

private SqlConnect sql;

并在一个方法中：

sql.doPost(request, response);

我收到以下错误：

java.lang.NullPointerException
crunch.FormProcess.doGet(FormProcess.java:27)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

这是目前的 SqlConnect 类（我省略了导入等）：

@WebServlet(name="sql",urlPatterns={"/sql"})
public class SqlConnect extends javax.servlet.http.HttpServlet {

    FormProcess process = new FormProcess();

    private static final long serialVersionUID = 1L;

    public SqlConnect() {

    }

    public void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        performTask(request, response);
    }

    public void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        performTask(request, response);
    }

    public void performTask(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        testJndiDataSource();
    }

    public void testJndiDataSource() {
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            InitialContext ctx = new InitialContext();
            DataSource ds = (DataSource) ctx.lookup("java:comp/env/jdbc/CrunchDB");

            conn = ds.getConnection();

            st = conn.createStatement();
            st.executeUpdate("INSERT INTO log " + "VALUES (20, '1', '1', " + process.salaryInt + ", "+ process.takeHomePAYE +", "+ process.takeHomeContractor +", 2)");


        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try { if (rs != null) rs.close(); } catch (SQLException e) { e.printStackTrace(); }
            try { if (st != null) st.close(); } catch (SQLException e) { e.printStackTrace(); }
            try { if (conn != null) conn.close(); } catch (SQLException e) { e.printStackTrace(); }
        }
    }

}

我确信有一种简单的方法可以做到这一点，我只是无法解决，正如我所说的 SqlConnect 类将自行运行良好。

干杯

4

1 回答 1

2

不幸的是，你现在的班级结构是有缺陷的。SqlConnect不应该是 的子类HttpServlet，因为人们永远不应该直接调用它，就好像它是一个网页一样。相反，只有FormProcess和您的其他实际 servlet 应该访问SqlConnect.

所以现在，您的代码应该如下所示：

public void testJndiDataSource(int salaryInt, double takeHomePAYE, String takeHomeContractor) {
    Connection conn = null;
    Statement st = null;
    ResultSet rs = null;
    try {
        InitialContext ctx = new InitialContext();
        DataSource ds = (DataSource) ctx.lookup("java:comp/env/jdbc/CrunchDB");

        conn = ds.getConnection();

        st = conn.createStatement();
        st.executeUpdate("INSERT INTO log " + "VALUES (20, '1', '1', " + process.salaryInt + ", "+ process.takeHomePAYE +", "+ process.takeHomeContractor +", 2)");


    } catch (Exception ex) {
        ex.printStackTrace();
    } finally {
        try { if (rs != null) rs.close(); } catch (SQLException e) { e.printStackTrace(); }
        try { if (st != null) st.close(); } catch (SQLException e) { e.printStackTrace(); }
        try { if (conn != null) conn.close(); } catch (SQLException e) { e.printStackTrace(); }
    }
}

然后，在FormProcess：

public void performTask(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {
    int salaryInt = //extract from form... 
    double takeHomePAYE = //extract from form... 
    String takeHomeContractor = //extract from form... 
    SqlConnect sqlConnect = new SqlConnect();
    sqlConnect.testJndiDataSource(salaryInt, takeHomePAYE, takeHomeContractor);
}

这是一种更合乎逻辑的方法来模拟您的网站应该如何工作。注意：现在的查询完全容易受到 SQL 注入的攻击。根据此处的说明将您更改Statement为：http: //docs.oracle.com/javase/tutorial/jdbc/basics/prepared.htmlPreparedStatement

于 2013-10-06T17:56:08.740 回答