反序列化文件并返回包含文件中对象的arraylist [英] De-serialize a file and return an arraylist containing the objects in the file

问题描述

我已经将一个arraylist序列化为一个文件，但是很难将它们反序列化回一个arraylist并打印出来。如何编辑我的代码？谢谢！

I have serialized an arraylist to a file, but have difficulties deserializing them back into an arraylist and print them. How can I edit my code? Thanks!

这是序列化方法：

    public static void writeMembersToDisk(ArrayList<Member> membersList) {
    ObjectOutputStream out = null;
    try {
        out = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream("members.s")));

        for(Member cmd : membersList) {
            out.writeObject(cmd);
        }
    } catch (Exception e) {
        System.err.println("Error: " + e.toString());
    } finally {
        try {
            out.close();
        } catch (IOException e) {
            System.err.println("Error: " + e.toString());
        }
    }
}

我不知道如何将文件反序列化回arraylist，这是我的代码：

I don't know how to deserialize the file back to the an arraylist, this is my code:

    public static ArrayList<Member> readMembersFromDisk() {

        ArrayList<Member> cmd = null;

        try {
            FileInputStream is = new FileInputStream("members.s");

            ObjectInputStream os = new ObjectInputStream(is);                           

            cmd = (ArrayList) os.readObject();

            os.close();  

        } catch (Exception e) {
            System.err.println("Error: " + e.toString());            
        }

        return cmd;

}

当我尝试打印数组列表时，出现错误： java.lang.ClassCastException：成员不能转换为java.util.ArrayList

When I try to print the arraylist, I get an error: "java.lang.ClassCastException: Member cannot be cast to java.util.ArrayList"

    public static void main(String[] args) {
    ArrayList<Member> list = MembersListFileManager.readMembersFromDisk();      
            System.out.println(list);
}

推荐答案

您正在写一个<$

You are writing one Member object at a time from the original list.

for(Member cmd : membersList) {
    out.writeObject(cmd);
}

但是在阅读时，您试图投射成员对象放入 ArrayList 中是错误的。

But while reading you're trying to cast a Member object into an ArrayList which is wrong.

您需要强制读取通过执行以下操作来反对成员：

You need to cast the read object to Member by doing something like this:

Member member = (Member) os.readObject();

但这只会获取序列化的第一个对象。要获取所有对象，请遍历并继续将每个成员对象添加到arraylist中。

But this will just fetch the first object serialized. To get all the objects, loop through and keep adding each member object read into the arraylist.

// Pseudo-code
loop till objects are there{
    Member member = (Member) os.readObject(); // read the object
    cmd.add(member); // add it to the list
}

其中一种循环方法是，

while (true) {
    try {
        Member member = (Member) os.readObject();
        // Do something with the object
    } catch (EOFException e) {
        break; // Break when the end-of-file is reached
    }
}
os.close();

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