写学生管理系统的时候遇到了问题...

[MOTEC]

存储操作主要是通过 FILE.IO MAP存储的 当我第二次使用时就会出现 如图所示的情况 无论存储还是查询 都会出现 null


下面是源码

package ListRegisterIO;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.EOFException;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.List;

public class UserInterface {
	//声明全局对象
	private	UserManagerByMap um; 
		
	//静态化文本数据库
	private static final String Save_Path="F://testStu.save";
	
	public UserInterface(){
		try {
			//检测是否有文件夹
			File CheckFile = new File(Save_Path);
			if (!CheckFile.exists()) {
				//如果没有则创建
				CheckFile.createNewFile();
			
				um = new UserManagerByMap();
				
				System.out.println("你是第一次使用我们的系统");
				} else {
				//从文件流中加载对象
				LoadUserManagerObject();
				System.out.println("系统加载完成");
			}
	
			
		
		} catch (IOException e) {
			System.out.println(e.getMessage());
		}
		
	}
	
	private UserManagerByMap LoadUserManagerObject() {
		// TODO Auto-generated method stub
		//输入对象
		ObjectInputStream ois =null;
		
		try {
			//从文件中加载对象
			ois=new ObjectInputStream(new BufferedInputStream(new FileInputStream(Save_Path)));
			//将读取到的对象强制转换成UserManagerByMap 对象
			UserManagerByMap um=(UserManagerByMap) ois.readObject();
			return um;
			
	    	}catch(EOFException e){
	    		//如果存在担对象加载为空  则返回一个新对象
	    		return new UserManagerByMap();
	    	}catch (FileNotFoundException e) {
			  // TODO Auto-generated catch block
	    		e.printStackTrace();
	    	} catch (IOException e) {
	    		// TODO Auto-generated catch block
	    		e.printStackTrace();
	    	} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
	    		e.printStackTrace();
		}finally{
			if(ois!=null){
				try {
					ois.close();
				} catch (IOException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
			
		}
		
		
		return null;
	}

	private void save(){
		 ObjectOutputStream oos = null;
		try {
			oos = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(Save_Path)));
			oos.writeObject(um);
		} catch (IOException e) {
			// TODO Auto-generated catch block
		e.printStackTrace();
		}finally{
			try {
				if (oos!= null) {
					oos.close();
				}
			} catch (IOException e3) {
				System.out.println("错误01：");
			}
			
		}
		
		
}
	
	
	public void run(){
			BufferedReader br = null;
			br= new BufferedReader(new InputStreamReader(System.in));
			String str = null;
			showInfo();
			try {
			while ((str = br.readLine()) != null) {
				if(str.equalsIgnoreCase("Q")){
					System.out.println("谢谢使用");
					
					break;
				}else if(str.equalsIgnoreCase("A")){
					add(br);
					
				}else if(str.equalsIgnoreCase("B")){
					delete(br);
					
				}else if(str.equalsIgnoreCase("C")){
					update(br);
				}else if(str.equalsIgnoreCase("D")){
					list();
				}else if(str.equalsIgnoreCase("L")){
					login(br);
				}else if(str.equalsIgnoreCase("F")){
					search(br);
					
				}else{
					System.err.println("请输入一个正确的 操作方式");
				}
				showInfo();
			}
		} catch (final Exception e) {
		 System.out.println(e.getMessage());
		}finally{
			try {
				if (br!= null) {
					br.close();
				}
			} catch(IOException e2) {
				System.out.println(e2.getMessage());
			}
				}
			
			
	}
	
	
	
	
	private void login(BufferedReader br) throws IOException {
		System.out.println("请输入用户名：");
		String UserName = br.readLine();
		System.out.println("请输入密码：");
		String PassWord=br.readLine();
		User u = um.login(UserName, PassWord);
		System.out.println("热了欢迎"+u.getUserName());
	}

	private void update(BufferedReader br) throws IOException {
		try {
			// TODO Auto-generated method stub
			System.out.println("请输入要更新的用户名：");
			String UserName = br.readLine();
			System.out.println("请输入新密码：");
			String PassWord = br.readLine();
			System.out.println("请输入新昵称：");
			String NickName = br.readLine();
			System.out.println("请输入新年龄：");
			int Age = Integer.parseInt(br.readLine());
			User u1 = new User(UserName, NickName, PassWord, Age);
			um.update(u1);
			System.out.println(UserName+"更新成功");
			save();
		} catch (NumberFormatException e) {
				System.err.println("输入的年龄格式不正确");
		}catch(UserException e){
				System.err.println(e.getMessage());
		}
		
	}

	private void delete(BufferedReader br) throws IOException {
		// TODO Auto-generated method stub
		System.out.println("请输入要删除的用户名：");
		String username=br.readLine();
		User u= um.loadUser(username);
		if(u==null){
			System.err.println("要删除的用户不存在");
		}else{
			um.Delete(username);
			System.out.println(username+"删除成功");
		}
		save();
	}

	private void search(BufferedReader br) throws IOException {
		System.out.println("请输入要查询的用户名：");
		String username=br.readLine();
		User u=um.loadUser(username);
		if(u==null){
			System.err.println("用户名不存在");
		}else{
			System.out.println(u);
		}
		
		
	}

	private void list(){
		List<User> list=um.list();
		for(User u:list){
			System.out.println(u);
		}
		
	}
	
	
	private void add(BufferedReader br){
		try {
		System.out.println("请输入用户名：");
		String UserName = br.readLine();
		System.out.println("请输入密码：");
		String PassWord=br.readLine();
		System.out.println("请输入昵称：");
		String NickName=br.readLine();
		System.out.println("请输入年龄：");
		int Age=Integer.parseInt(br.readLine());
		User user=new User(UserName,PassWord,NickName,Age);
		um.Add(user);
		System.out.println("添加用户成功");
		save();
		} catch (NumberFormatException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
	
		
		
	}
	
	
	public void showInfo(){
		System.out.println("请选择下列操作");
		System.out.println("------------------------------------------------------------------------------------------------");
		System.out.println("添加【A】                   删除【B】                修改【C】             列表【D】                   查询【F】   	    登陆【L】              退出【Q】  ");
		System.out.println("------------------------------------------------------------------------------------------------");
	}
	
	
	
}

[MOTEC]

MAP

package ListRegisterIO;

import java.io.Serializable;
import java.util.*;

public class UserManagerByMap implements Serializable {
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	List<String> Forbid = Arrays.asList("cmb","nmb","fandong");
	Map<String ,User> users;
		
	
	public UserManagerByMap() {
		users = new HashMap<String,User>();
	}

	public void Add(User user){
		if(Forbid.contains(user.getNickName())){
			throw new UserException(user.getUserName()+"该用户名停止注册");
		}
		if(users.containsKey(user.getUserName())){
			throw new UserException(user.getUserName()+"已存在"); 
			}
		
		users.put(user.getUserName(), user);
		System.out.println(user.getUserName()+"添加成功");
		
		
	}
	
	public void Delete(String userName){
		if(!users.containsKey(userName)){
			throw new UserException(userName+"不存在");
		}
		users.remove(userName);
		System.out.println(userName+"删除成功");
	}
	
	public void update(User user){
		if(!users.containsKey(user.getUserName())){
			throw new UserException(user.getUserName()+"不存在");
			
		}
		users.put(user.getUserName(), user);
		
	}
	
	public User loadUser(String userName){
		return users.get(userName) ;
	}
	
	public User login(String userName,String Password){
		User u = loadUser(userName);
		if(!users.containsKey(userName)){
			throw new UserException(userName+"不存在");
		}
		
		if(!Password.equals(u.getPassWord())){
			
			throw new UserException(userName+"密码错误");
		}
		
		System.out.println(u.getUserName()+"登陆成功");
		return u;
	}
	
	public List<User> list(){
		System.out.println("=======================已添加======================");
		//存储用户信息
		List<User> saveUser = new ArrayList<User>();
		//存储用户名
		Set<String> key= new HashSet<String>(users.keySet());
		for(String username:key){
			saveUser.add(users.get(username));
		}
		return saveUser;
	}
}

[汤雨飞]

调试一下就出来了， 类变量um在从文件流中加载的时候有误： LoadUserManagerObject（）方法中重新定义了一个局部变量um， 方法返回值又没有传递个类变量um，改下就行了。

[MOTEC]

引用 2 楼 tangyufei888 的回复:

调试一下就出来了， 类变量um在从文件流中加载的时候有误： LoadUserManagerObject（）方法中重新定义了一个局部变量um， 方法返回值又没有传递个类变量um，改下就行了。

恩 就是的 我已经改好了