这里只是一个新手。我刚刚使用MVC框架（JSP和Servlets）创建了一个简单的注册页面，并在数据库中注册它，当我试图运行它时，我收到了一个错误
Exception report:
SEVERE: Servlet.service() for servlet [Controller.RegistrationServlet] in context with path [/RegistrationApp] threw exception
java.lang.NullPointerException
at ModelDb.ModelDBConnect.registerUser(ModelDBConnect.java:55)
at Controller.RegistrationServlet.doPost(RegistrationServlet.java:63)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
这是我的源代码：
Registrationview.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Registration Form</title>
</head>
<style>
body {background-color: #101010 }
h3 {color:white}
td{color: white}
</style>
<body>
<h3>Registration Page</h3>
<br>
<form action="Registration" method="post">
<table>
<tr>
<td>Employee Id:</td>
<td><input type="text" name="EMPLOYEE_ID"> Job Id:</td><td><input type="text" name="JOB_ID"></td>
<tr>
<td>First Name:</td>
<td><input type="text" name="FIRST_NAME"> Salary:</td><td><input type="text" name="SALARY"></td>
</tr>
<tr>
<td>Last Name:</td>
<td><input type="text" name="LAST_NAME"> Commission:</td><td><input type="text" name="COMMISSION_PCT"></td>
</tr>
<tr>
<td>Email:</td>
<td><input type="text" name="EMAIL"> Manager Id:</td><td><input type="text" name="MANAGER_ID"></td>
</tr>
<tr>
<td>Phone Number:</td>
<td><input type="text" name="PHONE_NUMBER"> Department Id:</td><td><input type="text" name="DEPARTMENT_ID"></td>
</tr>
<tr>
<td>Hire Date:</td>
<td><input type="text" name="HIRE_DATE">
</tr>
</table><br>
<input type="submit" value="Register">
</form>
</body>
</html>
控制器：
RegistrationServlet
package Controller;
import java.io.IOException;
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 Model.RegistrationBean;
import ModelDb.ModelDBConnect;
@WebServlet("/Registration")
public class RegistrationServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 1) Retrieve all parameters from JSP Page
String EMPLOYEE_ID = request.getParameter("EMPLOYEE_ID");
String FIRST_NAME = request.getParameter("FIRST_NAME");
String LAST_NAME = request.getParameter("LAST_NAME");
String EMAIL= request.getParameter("EMAIL");
String PHONE_NUMBER = request.getParameter("PHONE_NUMBER");
String HIRE_DATE = request.getParameter("HIRE_DATE");
String JOB_ID = request.getParameter("JOB_ID");
String SALARY = request.getParameter("SALARY");
String COMMISSION_PCT = request.getParameter("COMMISSION_PCT");
String MANAGER_ID = request.getParameter("MANAGER_ID");
String DEPARTMENT_ID = request.getParameter("DEPARTMENT_ID");
//2) set all the values in the model class object
RegistrationBean rb = new RegistrationBean();
rb.setEMPLOYEE_ID(EMPLOYEE_ID);
rb.setFIRST_NAME(FIRST_NAME);
rb.setLAST_NAME(LAST_NAME);
rb.setEMAIL(EMAIL);
rb.setPHONE_NUMBER(PHONE_NUMBER);
rb.setHIRE_DATE(HIRE_DATE);
rb.setJOB_ID(JOB_ID);
rb.setSALARY(SALARY);
rb.setCOMMISSION_PCT(COMMISSION_PCT);
rb.setMANAGER_ID(MANAGER_ID);
rb.setDEPARTMENT_ID(DEPARTMENT_ID);
// 3) Call a method from ModelDBConnect class to insert data in the table
String sql ="Insert into EMPLOYEES" + "(EMPLOYEE_ID, FIRST_NAME, LAST_NAME, EMAIL, PHONE_NUMBER, HIRE_DATE, JOB_ID, SALARY, COMMISSION_PCT, MANAGER_ID, DEPARTMENT_ID) VALUES" +
"(?,?,?,?,?,?,?,?,?,?,?)";
int i = ModelDBConnect.registerUser(rb, sql);
if (i != 0) {
System.out.println("value inserted");
}
else {
System.out.println("value not inserted");
}
}
}
的JavaBean
RegistrationBean
package Model;
public class RegistrationBean {
private String EMPLOYEE_ID;
private String FIRST_NAME;
private String LAST_NAME;
private String EMAIL;
private String PHONE_NUMBER;
private String HIRE_DATE;
private String JOB_ID;
private String SALARY;
private String COMMISSION_PCT;
private String MANAGER_ID;
private String DEPARTMENT_ID;
public String getEMPLOYEE_ID() {
return EMPLOYEE_ID;
}
public void setEMPLOYEE_ID(String eMPLOYEE_ID) {
EMPLOYEE_ID = eMPLOYEE_ID;
}
public String getFIRST_NAME() {
return FIRST_NAME;
}
public void setFIRST_NAME(String fIRST_NAME) {
FIRST_NAME = fIRST_NAME;
}
public String getLAST_NAME() {
return LAST_NAME;
}
public void setLAST_NAME(String lAST_NAME) {
LAST_NAME = lAST_NAME;
}
public String getEMAIL() {
return EMAIL;
}
public void setEMAIL(String eMAIL) {
EMAIL = eMAIL;
}
public String getPHONE_NUMBER() {
return PHONE_NUMBER;
}
public void setPHONE_NUMBER(String pHONE_NUMBER) {
PHONE_NUMBER = pHONE_NUMBER;
}
public String getHIRE_DATE() {
return HIRE_DATE;
}
public void setHIRE_DATE(String hIRE_DATE) {
HIRE_DATE = hIRE_DATE;
}
public String getJOB_ID() {
return JOB_ID;
}
public void setJOB_ID(String jOB_ID) {
JOB_ID = jOB_ID;
}
public String getSALARY() {
return SALARY;
}
public void setSALARY(String sALARY) {
SALARY = sALARY;
}
public String getCOMMISSION_PCT() {
return COMMISSION_PCT;
}
public void setCOMMISSION_PCT(String cOMMISSION_PCT) {
COMMISSION_PCT = cOMMISSION_PCT;
}
public String getMANAGER_ID() {
return MANAGER_ID;
}
public void setMANAGER_ID(String mANAGER_ID) {
MANAGER_ID = mANAGER_ID;
}
public String getDEPARTMENT_ID() {
return DEPARTMENT_ID;
}
public void setDEPARTMENT_ID(String dEPARTMENT_ID) {
DEPARTMENT_ID = dEPARTMENT_ID;
}
}
连接数据库：
ModelDBConnect.java
package ModelDb;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import Model.RegistrationBean;
public class ModelDBConnect {
// JDBC driver name and database
static final String JDBC_Driver = "oracle.jdbc.OracleDriver";
static final String DB_URL = "jdbc:oracle:thin:@//localhost:1521/XE";
// Database credentials
static final String USERNAME = "hr";
static final String PASSWORD = "hr1";
// method to connect to the database
private static Connection connect() {
Connection con = null;
// Register the JDBC Driver
try {
Class.forName("oracle.jdbc.OracleDriver");
// open a connection
System.out.println("Connection to the database");
con=DriverManager.getConnection(DB_URL, USERNAME, PASSWORD);
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return con;
}
public static int registerUser(RegistrationBean rb, String sql) {
int i = 0;
Connection con = connect();
try {
PreparedStatement ps =con.prepareStatement(sql);-------Error here!
ps.setString(1, rb.getEMPLOYEE_ID());
ps.setString(2, rb.getFIRST_NAME());
ps.setString(3, rb.getLAST_NAME());
ps.setString(4, rb.getEMAIL());
ps.setString(5, rb.getPHONE_NUMBER());
ps.setString(6, rb.getHIRE_DATE());
ps.setString(7, rb.getJOB_ID());
ps.setString(8, rb.getSALARY());
ps.setString(9, rb.getCOMMISSION_PCT());
ps.setString(10, rb.getMANAGER_ID());
ps.setString(11, rb.getDEPARTMENT_ID());
i=ps.executeUpdate();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return i;
}
}
谢谢！
答案 0 :(得分：1)
由于您的Connection con = connect();方法失败，我猜您的connect()被指定为空。
不是在失败时抛出异常，而是简单地打印堆栈跟踪 - 然后继续，好像什么也没发生。 （“好的，现在怎样？”）
请查找并查看生成的堆栈跟踪，以获取有关连接失败原因的其他一些线索。它可能是无效的连接字符串，用户名/密码或本地数据库本身的问题。
你最好重新抛出异常，或者根本不抓住它，并声明它可以作为方法的一部分抛出。然后，您可以依赖connect()返回有效连接 - 或者以异常方式失败。
按原样，在尝试使用它之前，首先需要检查con是否为null。当然，尝试在.prepareStatement上调用con时抛出NullPointerException，这是空的。