如何从ObjectInputStream读取所有对象 [英] How to read all objects from ObjectInputStream

问题描述

我有一个包含一些信息的文件，如何读取所有信息?

I have a file with some info how can I read all info?

Name names;    
try (FileInputStream fileInputStream = new FileInputStream(file)) {
            ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
            names = (Name) objectInputStream.readObject();
        } catch (IOException | ClassNotFoundException e) {
            e.printStackTrace();
        }

推荐答案

您有几种解决方案，具体取决于输入内容:

You have several solution, all depending on the input:

• 您可以迭代直到流被完全用尽:我认为这是我提供给您的解决方案中最糟糕的解决方案.更糟糕的是，您正在检查是否已达到EOF，同时您应该知道完成的时间(例如:文件格式错误).

• You can iterate until the stream is fully consumed: I think that is the worse solution out of those I provide you. It is worse because you are checking if EOF was reached, whilst you should know when you're done (eg: your file format is wrong).

Set<Name> result = new HashSet<>();
try { 
  for (;;) { 
    result.add((Name)objectInputStream.readObject());
  }
} catch (EOFException e) {
  // End of stream
} 
return result;

产生输入时，序列化一个集合并在其上调用 readObject().只要每个对象都实现了 Serializable .

When producing the input, serialize a collection and invoke readObject() on it. Serialization should be able to read the collection, as long as each object implements Serializable.

static void write(Path path, Set<Name> names) throws IOException {
  try (OutputStream os = Files.newOutputStream(path);
       ObjectOutputStream oos = new ObjectOutputStream(os)) {
    oos.writeObject(names);    
  }       
} 

static Set<Name> read(Path path) throws IOException {
  try (InputStream is = Files.newInputStream(path);
       ObjectInputStream ois = new ObjectInputStream(is)) {
    // WARN Files.newInputStream is not buffered; ObjectInputStream might
    // be buffered (I don't remember).
    return (Set<Name>) ois.readObject();
  }
}

在生成输入时，可以添加一个 int 来指示要读取的对象的数量，并对其进行迭代:如果您真的不在乎该对象，这很有用.集合( HashSet ).生成的文件将较小(因为您将没有 HashSet 元数据).

When producing the input, you can add a int indicating the number of object to read, and iterate over it: this is useful in case where you don't really care of the collection (HashSet). The resulting file will be smaller (because you won't have the HashSet metadata).

int result = objectInputStream.readInt();
Name[] names = new Name[result]; // do some check on result!
for (int i = 0; i < result; ++i) {
  names[i] = (Name) objectInputStream.readObject();
}

此外， Set 很好，但是由于它们使用 hashCode()/ equals()删除重复项，如果您的事实之后，等于/ hashCode 的定义发生了变化(例如:您的名称区分大小写，现在则不区分大小写，例如: new名称("AA").等于(新名称("aa"))).

Also, Set are good, but since they remove duplicate using hashCode()/equals() you may get less object if your definition of equals/hashCode changed after the fact (example: your Name was case sensitive and now it is not, eg: new Name("AA").equals(new Name("aa"))).

这篇关于如何从ObjectInputStream读取所有对象的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！