Java 我的servlet正在抛出异常

我试图构建一个登录面板，但是当我试图从控制器（LoginController）调用模型内部的方法（CustomerButil）时，它抛出异常。我对JSP有些陌生，无法调试它。代码和控制台输出如下所示：

登录表单

    <form action="LoginController" method="POST" id="login-form">

        <header class="text-center">
            <h2 class="font-light">Login</h2>
        </header>

        <input type="hidden" name="command" value="LOAD">

        <label>Username : </label>
        <input type="text" name="username" placeholder="Username" class="form-control" required /><br>

        <label>Password : </label>
        <input type="password" name="password" placeholder="Password" class="form-control" required /><br>

        <input type="submit" value="Login" class="btn btn-primary" /><br><br>

        <span style="color:black">New users</span> <a href="user-register.jsp">Register here</a>

    </form>

---

我不知道我是错过了什么，还是做错了什么。请帮忙。提前感谢！：）

您可以将Springbean注入到servlet中

ApplicationContext context = WebApplicationContextUtils.getWebApplicationContex t(getServletContext());
InterfaceType bean = (InterfaceType)context.getBean("BeanName");

---

我怀疑CustomerButil没有连接属性，因此在调用时为null。在这一行->客户=客户但是。选择客户（用户名，md5）；//在此语句中引发异常。@user3138997。。。但我的eclipse不会弹出任何警告或错误，比如找不到方法之类的。这是一个运行时异常，而不是编译错误。尝试初始化CustomerButil。CustomerButil CustomerButil=新CustomerButil（数据源）；（我的错误最初我以为这是一个Spring MVC）您的

catch（异常e）{throw new ServletException（）；}

是第一个问题-这意味着您只能知道“出了什么问题”。您至少应该将其更改为throw

newservletexception（e）

，以便查看原始异常的详细信息。不过，我建议尽可能捕获更具体的异常，并且不要声明只抛出

异常的方法，除非您必须这样做。@user3138997。。。谢谢你！！你的解决方案奏效了。我在init块中初始化了CustomerButil，它成功了！谢谢：）
package com.loginpanel.web;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;


import javax.sql.DataSource;


public class CustomerDbUtil {
    private DataSource dataSource;

    public CustomerDbUtil(DataSource theDataSource) {
        dataSource = theDataSource;
    }

    public boolean addCustomer(Customer theCustomer) throws Exception {

        // Declare the DB objects
        Connection con = null;
        PreparedStatement myStmt = null;
        boolean isExecuted = false;

        try{
            // Get the connection 
            con = dataSource.getConnection();

            // Write the SQL for adding a student
            String sql = "INSERT INTO customers ( "
                    + " first_name, last_name, username, md5, country) "
                    + "VALUES (?, ?, ?, ?, ?)";

            // Prepare the statement
            myStmt = con.prepareStatement(sql);

            // Add the params
            myStmt.setString(1, theCustomer.getCustomerFirstName());
            myStmt.setString(2, theCustomer.getCustomerLastName());
            myStmt.setString(3, theCustomer.getUsername());
            myStmt.setString(4, theCustomer.getMd5());
            myStmt.setString(5, theCustomer.getCountry());

            // Execute the SQL statement
            if(myStmt.execute()){
                isExecuted = true;
            } else {
                isExecuted = false;
            }

        } catch(Exception e) {
            e.printStackTrace();
        } finally {
            // Clear the JDBC objects
            close(con, myStmt, null);
        }
        return isExecuted;
    }


    public Customer selectCustomer(String user, String md) throws Exception {

        Customer theCustomer = null;

        // Get the connection
        Connection con = null;
        PreparedStatement myStmt = null;
        ResultSet myRs = null;

        System.out.println("What??");

        try {

            con = dataSource.getConnection();

            // Write the SQL statement
            String sql = "SELECT * FROM login_module.customers WHERE username = ? AND md5 = ?";

            // Prepare the statement
            myStmt = con.prepareStatement(sql);

            // Add the parameters
            myStmt.setString(1, user);
            myStmt.setString(2, md);

            // Execute the query
            myRs = myStmt.executeQuery();

            System.out.println("Hello");

            // Fetch the student details
            if(myRs.next()) {
                int customerId = myRs.getInt("customer_id");
                String firstName = myRs.getString("first_name");
                String lastName = myRs.getString("last_name");
                String user_name = myRs.getString("username");
                String md5 = myRs.getString("md5");
                String country = myRs.getString("country");

                // Create a customer object
                theCustomer = new Customer(customerId, firstName, lastName, user_name, md5, country);

            } else {
                throw new Exception("Could not find the customer");
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            close(con, myStmt, myRs);
        }

        return theCustomer;

    }


    public void close(Connection conn, Statement stm, ResultSet rs) throws Exception{

        try{
            // Close the objects
            if(conn!=null) {
                conn.close();
            }
            if(stm!=null) {
                stm.close();
            }
            if(rs!=null) {
                rs.close();
            }
        } catch(Exception e) {
            e.printStackTrace();
        }

    }

    public List<Customer> getCustomers() throws Exception{

        List<Customer> listCustomer = new ArrayList<>();

        Connection con = null;
        Statement myStmt = null;
        ResultSet myRs = null;

        try {

                // Get the connection
                con = dataSource.getConnection();

                // Create SQL statements
                String sql = "SELECT * FROM login_module.customers";

                // Prepare the statement
                myStmt = con.createStatement();

                // Execute the statement and store it into the ResultSet
                myRs = myStmt.executeQuery(sql);

                // Fetch the data one-by-one and add it to the list
                while(myRs.next()){
                    int id = myRs.getInt("customer_id");
                    String firstName = myRs.getString("first_name");
                    String lastName = myRs.getString("last_name");
                    String username = myRs.getString("username");
                    String md5 = myRs.getString("md5");
                    String country = myRs.getString("country");


                    Customer theCustomer = new Customer (id, firstName, lastName, username, md5, country);

                    // Add it to the list
                    listCustomer.add(theCustomer);

                }

            } catch ( Exception e ) {
                e.printStackTrace();
            } finally {

                // Close the connection objects
                close(con, myStmt, myRs );

            }

            // Return the list
            return listCustomer;


    }

}

inside validate
May 13, 2017 7:24:00 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [com.loginpanel.web.LoginController] in context with path [/loginpanel] threw exception [null] with root cause
javax.servlet.ServletException
    at com.loginpanel.web.LoginController.doGet(LoginController.java:38)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:292)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:240)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:207)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:616)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:522)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1095)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:672)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1504)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1460)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

ApplicationContext context = WebApplicationContextUtils.getWebApplicationContex t(getServletContext());
InterfaceType bean = (InterfaceType)context.getBean("BeanName");