有关JSP&的问题SQL。 Java Web应用程序 [英] Questions about JSP & SQL. Java web application

问题描述

我最近正在开发一个Java Web应用程序，该应用程序必须专注于CRUD（您知道）。但我对阅读&更新和删除操作（三个操作）。只有创建操作才能正常工作。详细地说，我正在使用的Java Web应用程序尚未完成。在我的代码内部，名为 findUsers的函数用于实现读取操作。顺便说一句，我已经检查了很长时间的代码。我猜问题可能出在findUsers函数中（不确定，只是一个假设）。每次我尝试键入R来调用该函数时，Netbeans都会返回用户不存在。我不知道为什么此外，数据库已成功连接。 在此处输入图片描述这张照片是我的数据库结构。

I am recently working on making a Java web application, which must focus on CRUD(You know). But I am stuck with the read & update & delete operations(Three operations). Only Create Operation works fine. In detailed, the Java web application I am working on is not completed so far. Inside my code, the function called "findUsers" is used to implement read operation. By the way, I already checked code for a long period of time. I guess the problem may be in findUsers function(not sure, just an assumption). Every time, I try to type R to invoke that function, Netbeans returns "User does not exist". I don't know why. Moreover, the database is connected successfully. enter image description here This photo is my database structure.

//read operation
   public User findUsers(String email, String password) throws SQLException {
    String sqll = "SELECT * FROM XWB.USERS WHERE EMAIL = ' " + email + " ' AND PASSWORD = ' " + password + " ' ";
    // " SELECT * FROM XWB.USERS WHERE EMAIL = ' " + email + " ' AND PASSWORD = ' " + password + " ' "; 
    //select * from XWB.Users where EMAIL = 'TargetEmail' and PASSWORD = 'TargetPassword';
    ResultSet rs = st.executeQuery(sqll);

    while (rs.next()) {
        String UserEmail = rs.getString("EMAIL");
        String UserPassword = rs.getString("PASSWORD");
        if (UserEmail.equals(email) && UserPassword.equals(password)) {
            String UserName = rs.getString("NAME"); 
            String UserGender = rs.getString("GENDER");
            String UserColor = rs.getString("FAVOURITECOLOR");
            return new User(UserEmail, UserName, UserPassword, UserGender, UserColor);
        }
    }
    return null;
}

TestDB.java（我使用此类来测试DBManager）

TestDB.java(I use this class to test the DBManager)

 // findUsers()
    private void testRead() throws SQLException {
        System.out.print("User email: ");
        String email = in.nextLine();
        System.out.print("User password: ");
        String password = in.nextLine();
        User user = db.findUsers(email, password); // returns nothing
        //System.out.println(user);
        if( user != null) {
            System.out.println("User " + user.getName() + " exists in the database.");
        }else { //user == null
            System.out.println("User does not exit.");
        }
    }

这是我从Netbeans获得的结果。它总是告诉我用户不存在。
在此处输入图像描述

This is the result I got from Netbeans. It always tells me "User does not exist. " enter image description here

推荐答案

在您的代码中，您有返回null 的功能，检查您的调用类 if（user！= null）将返回false，并且<$ c $中的 else 部分返回$ c> if语句将被执行。因此要克服以下更改：

In your code you have return null so when this get check at your calling class if( user != null) will return false and the else part of your if-statement will get executed.So to overcome do below changes :

您的方法将如下所示：

User user; //create class object
String sqll = "SELECT * FROM XWB.USERS WHERE EMAIL = ? AND PASSWORD = ? ";
PreparedStatement ps = con.prepareStatement(
 sqll);
//setting value for "?" 
ps.setString(1, email);
ps.setString(2, password);
//execute query
ResultSet rs = ps.executeQuery();
//if found
if (rs.next()) {
 //fetch
 String UserEmail = rs.getString("EMAIL");
 String UserPassword = rs.getString("PASSWORD");
 String UserName = rs.getString("NAME");
 String UserGender = rs.getString("GENDER");
 String UserColor = rs.getString("FAVOURITECOLOR");
 //pass in constructor
 user = new User(UserEmail, UserName, UserPassword, UserGender, UserColor);
} else {
 //set the object to null (no match)
 user = null;
}
//send object back
return user;

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