无法调用DAO类的方法.不能从静态上下文引用非静态方法插入

Question

我正在尝试构建一个注册表单，其中一个配置文件映像作为blob进入mysql数据库。除了registration.jsp之外，我还有一个RegisterServlet 1.java、一个UsersDAO.java、一个ConnectionManager.java和一个Users.java。我的mysql数据库屏幕截图是为表"Users"附上的。我收到了RegisterServlet 1.java的解析文件错误。更具体地说，netbeans给了我一个提示，

'non static method insert(Users) cannot be referenced from a static context. 
 Unreported exception ClassNotFound Exception must be caught or declared to be thrown'

---

请参阅所附的屏幕截图，因为它将显示我得到的netbeans提示。有人能告诉我如何纠正错误，并从表单中获取用户详细信息以进入mysql数据库吗？

package com.nszhost.nsztrial;

import java.io.IOException;
import java.util.Scanner;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
@MultipartConfig
public class RegisterServlet1 extends HttpServlet {        
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    Part fname1= request.getPart("fname");
    Part gender1= request.getPart("gender");
    Part email1= request.getPart("email");
    Part userid1= request.getPart("userid");
    Part password1= request.getPart("password");
    Part profile_img1= request.getPart("profile_img");
    Scanner scanner1  = new Scanner( fname1.getInputStream());
    String fname2= scanner1.nextLine();
    Scanner scanner2  = new Scanner( gender1.getInputStream());
    String gender2= scanner2.nextLine();
    Scanner scanner3  = new Scanner( email1.getInputStream());
    String email2= scanner3.nextLine();
    Scanner scanner4  = new Scanner( userid1.getInputStream());
    String userid2= scanner4.nextLine();
    Scanner scanner5  = new Scanner( password1.getInputStream());
    String password2= scanner5.nextLine();



    Users user=new Users();
    user.setEmail(email2);
    user.setFname(fname2);
    user.setGender(gender2);
    user.setPassword(password2);
    user.setUserid(userid2);
    user.setProfile_img((Part) profile_img1);

        UsersDAO.insert(user);


}

}

---

package com.nszhost.nsztrial;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class UsersDAO {
private static Connection conn = ConnectionManager.getInstance().getConnection();
public static void insert(Users user) throws ClassNotFoundException, SQLException, IOException{
    Class.forName("com.mysql.jdbc.Driver");
PreparedStatement ps;
ps = conn.prepareStatement("insert into users (fname,gender,email,userid,password,profile_img) values(?,?,?,?,?,?)");
ps.setString(1, user.getFname());
ps.setString(2, user.getGender());
ps.setString(3, user.getEmail());
ps.setString(4, user.getUserid());
ps.setString(5, user.getPassword());

        // size must be converted to int otherwise it results in error
ps.setBinaryStream(6, user.getProfile_img().getInputStream(), (int)  user.getProfile_img().getSize());
ps.executeUpdate();
conn.commit();

    }
}

---

package com.nszhost.nsztrial;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class ConnectionManager {
        private static ConnectionManager instance = null;
        private final String USERNAME =     "root";
        private final String PASSWORD =     "****";
        private final String CONN_STRING = "jdbc:mysql://localhost/jdbc";
        private Connection conn = null;
        private ConnectionManager(){
        }
        public static ConnectionManager getInstance(){
            if(instance == null){
                instance = new ConnectionManager();
            }
            return instance;
        }
        private boolean openConnection(){
            try {
                conn = DriverManager.getConnection(CONN_STRING, USERNAME, PASSWORD);
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            return true;
        }
        public Connection getConnection(){
                if(conn == null){
                    if(openConnection()){
                            System.out.println("Connection Opened");
                            return conn;
                    }else{
                        return null;
                    }
                }
                return conn;
        }
        public void close(){
            System.out.println("Closing Connection");
            try {
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            conn = null;
        }
}

---

package com.nszhost.nsztrial;
import javax.servlet.http.Part;
public class Users {

private int id;
private String fname;
private String gender;
private String email;
private String userid;      
private String password;   
private Part profile_img;
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getFname() {
    return fname;
}
public void setFname(String fname) {
    this.fname = fname;
}
public String getGender() {
    return gender;
}
public void setGender(String gender) {
    this.gender = gender;
}
public String getEmail() {
    return email;
}
public void setEmail(String email) {
    this.email = email;
}
public String getUserid() {
    return userid;
}
public void setUserid(String userid) {
    this.userid = userid;
}
public String getPassword() {
    return password;
}
public void setPassword(String password) {
    this.password = password;
}

public Part getProfile_img() {
    return profile_img;
}
public void setProfile_img(Part profile_img) {
    this.profile_img = (Part)  profile_img;
}

}

netbeans提示屏幕截图mysql表"用户"

Answer 1

我想这是某种教程，所以我会忽略代码中的不同设计缺陷。

由于您的方法insert已经是static，我想NetBeans需要重新编译项目以消除该提示。

对于ClassNotFoundException：您声明了方法public static void insert(Users user) throws ClassNotFoundException [...]。由于ClassNotFoundExeption是一个已检查的异常，您必须重新抛出或捕获该异常。我想点击alt+enter（正如NetBeans在屏幕截图中所建议的那样）会显示这两个选项。

如果您不确定已检查和未检查的异常，我建议您阅读一些关于它们的信息，因为它们是java语言的核心概念。这似乎是一个很好且简短的解释。