类强制转换异常读取显示对象的ArrayList的写入文件

Question

/**
     * A method that writes variables in a file for shows in the program.
     * 
     * @author 
     * @version (1.2 2022.01.05)
     */
    public void writeShowData(String fileName) throws FileNotFoundException{
        String showPath = "c:\\Users\\COMPUTER\\bluej files\\projects\\chapter15\\willem\\CinemaReservationSystemFiles\\";
        try
        {
            FileOutputStream fos = new FileOutputStream(showPath+fileName,true);
            ObjectOutputStream oos = new ObjectOutputStream(fos);
            oos.writeObject(show);
            oos.flush();
            oos.close();
        }catch (IOException e) {
            e.printStackTrace();
        }

    }
    
    /**
     * A method that reads variables in a file for shows setup use in the program.
     * 
     * @author 
     * @version (1.2 2022.01.05)
     */
    public void readShowData(String fileName) throws FileNotFoundException {          
        try
        {   FileInputStream fis = new FileInputStream(fileName);
            ObjectInputStream ois = new ObjectInputStream(fis);
            List <Show>shows =(List<Show>)ois.readObject();
            ois.close();
            System.out.println(shows.toString());// for testing    
        }
        catch (IOException e) {
            e.printStackTrace();
        }catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }  

行：列表

类显示不能被强制转换到类java.util.列表（等等...

我尝试了很多东西，但都没能成功。

我制作了类show和相关的类Serializable，然后将其写入shows.ser但是当它读取时出错了。

谁能帮我解决这个问题？




Answer 1

匿名用户

我解决了你的问题如下。首先，你需要改变你的写作方法。如果数据文件不存在，则需要为流头创建一个常规（无附加）fileoutstream，否则将得到java。木卫一。StreamCorruptedException（参考）<代码>文件输出流的创建方式应与下一次添加不同。

public static void writeShowData(String fileName) {
        String showPath = "E:\\path\\";
        try {
            File file = new File(showPath + fileName);
            ObjectOutputStream oos;
            if(file.exists()) {
                FileOutputStream fos = new FileOutputStream(file.getAbsolutePath(), true); // with reset fos
                oos = new ObjectOutputStream(fos) {
                    protected void writeStreamHeader() throws IOException {
                        reset();
                    }
                };
            } else {
                FileOutputStream fos = new FileOutputStream(file.getAbsolutePath()); // regular fos
                oos = new ObjectOutputStream(fos);
            }
            
            oos.writeObject(show);
            oos.flush();
            oos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

其次，你需要修改你的阅读方法。如果你的FileInputStream有数据，你需要迭代来添加你的列表。

public static void readShowData(String fileName) {
        try {
            FileInputStream fis = new FileInputStream("E:\\path\\" + fileName);
            ObjectInputStream ois = new ObjectInputStream(fis);

            List<Show> shows = new ArrayList<>();
            while (fis.available() > 0) {
                Show s = (Show) ois.readObject();
                System.out.println(s.number);
                shows.add(s);
            }

            ois.close();
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }