Question

任何人都可以帮助我吗？当参数中没有空值时，为什么会收到此错误？

 You have an error in your SQL syntax; check the manual that corresponds to your MySQL    
 server version for the right syntax to use near 'null' at line 1

输入正常，代码接收它们，我唯一怀疑的是代码末尾的“VALUES”方法返回null。一点帮助PLZ？

            String theuser = (String) sInput.readObject();
            display(theuser);
            String thepass = (String) sInput.readObject();
            display(thepass);
            String thename = (String) sInput.readObject();
            display(thename);
            String thephone = (String) sInput.readObject();
            display(thephone);
            String themail = (String) sInput.readObject();
            display(themail);
            try{
                  //STEP 2: Register JDBC driver
                  Class.forName("com.mysql.jdbc.Driver");

                  //STEP 3: Open a connection
                  System.out.println("Connecting to a selected 
database...");
                  conn = DriverManager.getConnection(DB_URL, USER, 
 PASS);
                  System.out.println("Connected database 
 successfully...");


 // create output first
            sOutput = new ObjectOutputStream(socket.getOutputStream());
            sInput  = new ObjectInputStream(socket.getInputStream());
            // read the username
            String theuser = (String) sInput.readObject();
            display(theuser);
            String thepass = (String) sInput.readObject();
            display(thepass);
            String thename = (String) sInput.readObject();
            display(thename);
            String thephone = (String) sInput.readObject();
            display(thephone);
            String themail = (String) sInput.readObject();
            display(themail);
            try{
                  //STEP 2: Register JDBC driver
                  Class.forName("com.mysql.jdbc.Driver");

                  //STEP 3: Open a connection
                  System.out.println("Connecting to a selected 
database...");
                  conn = DriverManager.getConnection(DB_URL, USER, 
 PASS);
                  System.out.println("Connected database 
 successfully...");

                  //STEP 4: Execute a query
                  System.out.println("Inserting records into the 
table...");
                  stmt = conn.createStatement();

                  String sql = "INSERT INTO ofuser " +
                               VALUES 
(theuser,thepass,encrypted,thename,themail,4234,23432,thephone);
                  stmt.executeUpdate(sql);
               //   sql = "INSERT INTO Registration " +
               //                "VALUES (101, 'Mahnaz', 'Fatma', 25)";
               //   stmt.executeUpdate(sql);
               //   sql = "INSERT INTO Registration " +
              //                 "VALUES (102, 'Zaid', 'Khan', 30)";
               //   stmt.executeUpdate(sql);
               //   sql = "INSERT INTO Registration " +
              //                 "VALUES(103, 'Sumit', 'Mittal', 28)";
             //     stmt.executeUpdate(sql);
            //      System.out.println("Inserted records into the 
 table...");

               }catch(SQLException se){
                  //Handle errors for JDBC
                  se.printStackTrace();
               }catch(Exception e){
                  //Handle errors for Class.forName
                  e.printStackTrace();
               }finally{
                  //finally block used to close resources
                  try{
                     if(stmt!=null)
                        conn.close();
                  }catch(SQLException se){
                  }// do nothing
                  try{
                     if(conn!=null)
                        conn.close();
                  }catch(SQLException se){
                     se.printStackTrace();
                  }//end finally try
               }//end try





        }
        catch (IOException e) {
            display("Exception creating new Input/output Streams: " + 
e);
            return;
        }
        // have to catch ClassNotFoundException
        // but I read a String, I am sure it will work
        catch (ClassNotFoundException e) {
        }

    }

    // what will run forever

        // remove myself from the arrayList containing the list of the
        // connected Clients
    public void main(String[] args) {
        // start server on port 1500 unless a PortNumber is specified 
        int portNumber = 1500;
        switch(args.length) {
            case 1:
                try {
                    portNumber = Integer.parseInt(args[0]);
                }
                catch(Exception e) {
                    System.out.println("Invalid port number.");
                    System.out.println("Usage is: > java Server 
 [portNumber]");
                    return;
                }
            case 0:
                break;
            default:
                System.out.println("Usage is: > java Server 
 [portNumber]");
                return;

        }
        // create a server object and start it
        Server server = new Server(portNumber);
        server.start();
    }
    // try to close everything
    private void close() {
        // try to close the connection
        try {
            if(sOutput != null) sOutput.close();
        }
        catch(Exception e) {}
        try {
            if(sInput != null) sInput.close();
        }
        catch(Exception e) {};
        try {
            if(socket != null) socket.close();
        }
        catch (Exception e) {}
    }

    /*
     * Write a String to the Client output stream
     */
    private boolean writeMsg(String msg) {
        // if Client is still connected send the message to it
        if(!socket.isConnected()) {
            close();
            return false;
        }
        // write the message to the stream
        try {
            sOutput.writeObject(msg);
        }
        // if an error occurs, do not abort just inform the user
        catch(IOException e) {
            display("Error sending message to " );
            display(e.toString());
        }
        return true;
    }
}

public String VALUES(String theuser, String thepass,String encrypted,
        String thename, String themail, Object object2, Object object3,
        String thephone) {
    // TODO Auto-generated method stub
    return null;
}

//public void main(String[] args) {


    //   System.out.println("Goodbye!");
//  }//end main

Answer 1

String sql = "INSERT INTO ofuser " +
                               VALUES 
(theuser,thepass,encrypted,thename,themail,4234,23432,thephone);

上面的语法错误。它甚至不会编译。值应该用引号括起来。还要注意内部引用。

String sql = "INSERT INTO ofuser VALUES ('" +  theuser + "','" + thepass + "','....)";

Answer 2

您发送的SQL语句中存在问题 - 我假设其中一个值：

（theuser，thepass，加密，thename，themail，4234,23432，thephone）

设置为null。尝试将字符串打印到控制台，或通过调试器运行它以查看哪些变量为空。

希望有所帮助！

在mysql代码中接收null错误

2 个答案: