java - Java/MySQL:从Java Web应用程序(TomCat v7.0)将行插入表中

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

我还有一个用于将数据添加到MySQL数据库的新行的类，该类称为“ SqlConnect.java”。如果我在服务器上单独运行它，这也可以正常工作（即，它正确地在表上插入了一行）。

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)

此刻是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(); }
        }
    }

}

我敢肯定有一种简单的方法可以解决这个问题，因为我说SqlConnect类本身可以很好地运行。

干杯

最佳答案

不幸的是，您现在拥有的类结构存在缺陷。 SqlConnect不应是HttpServlet的子类，因为人们永远不应该像调用网页一样直接调用它。取而代之的是，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中：

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);
}

这是对网站的工作方式进行建模的更合乎逻辑的方法。注意：目前的查询完全容易受到SQL注入的攻击。按照此处的说明将Statement更改为PreparedStatement：http://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html

关于java - Java/MySQL:从Java Web应用程序(TomCat v7.0)将行插入表中，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/19211798/