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我想構建一個登錄面板，但是當我嘗試從控制器（LoginController）調用模型內部的一個方法（CustomerDbUtil）時，它會拋出異常。我對JSP有點新，而且我無法調試它。與控制檯輸出沿着代碼如下所示：我的servlet拋出異常
登錄形式
<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>
的LoginController（Controller類）
package com.loginpanel.web;
import java.io.IOException;
import java.io.PrintWriter;
import java.security.MessageDigest;
import javax.annotation.Resource;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
/**
* Servlet implementation class LoginController
*/
@WebServlet("/LoginController")
public class LoginController extends HttpServlet {
private static final long serialVersionUID = 1L;
@Resource(name="jdbc/login_module")
DataSource datasource;
private CustomerDbUtil customerDbUtil;
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
// Get the form data
String username = request.getParameter("username");
String md5 = md5(request.getParameter("password"));
Customer theCustomer = validate(username, md5);
} catch (Exception e) {
throw new ServletException(); // Throws this exception
}
}
private Customer validate(String username, String md5) throws Exception {
Customer theCustomer;
System.out.println("inside validate"); // Gets printed in the console
try {
theCustomer = customerDbUtil.selectCustomer(username, md5); // Throws Exception at this statement
System.out.println("inside try"); // Not printed in the console
if(theCustomer==null) {
return null;
}
} catch(Exception e) {
throw new ServletException();
}
return theCustomer;
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// Redirect back to the login page as the url does not support direct page access
RequestDispatcher dispatcher = request.getRequestDispatcher("./");
request.setAttribute("message", "You need to login first");
dispatcher.forward(request, response);
}
// Hash the string to MD5
private String md5(String str) throws Exception {
String plainText = str;
StringBuffer hexString = new StringBuffer();
if(plainText!=null) {
MessageDigest mdAlgorithm = MessageDigest.getInstance("MD5");
mdAlgorithm.update(plainText.getBytes());
byte[] digest = mdAlgorithm.digest();
for (int i = 0; i < digest.length; i++) {
plainText = Integer.toHexString(0xFF & digest[i]);
if (plainText.length() < 2) {
plainText = "0" + plainText;
}
hexString.append(plainText);
}
}
return hexString.toString();
}
}
CustomerDbUtil（型號）
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;
}
}
錯誤日誌
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)
如果我錯過了一些東西，或做不是有點錯了，我不知道。請幫忙。提前致謝！ :)
我懷疑你的customerDbUtil不屬性連接，因此在調用時它是空的。在這一行 - > theCustomer = customerDbUtil.selectCustomer（username，md5）; //在此語句中引發Exception。 – user3138997
@ user3138997 ...但我的eclipse不會彈出單個警告或錯誤，例如找不到方法或其他東西。 –
這是一個運行時異常，而不是編譯錯誤。嘗試初始化customerDbUtil。 CustomerDbUtil customerDbUtil = new customerDbUtil（datasource）; （我的錯誤最初我以爲這是一個Spring MVC） – user3138997