使用 FileInputStream 读取 XML 文件（对于 Java）？

Reading an XML File using FileInputStream (for Java)?

提问by ParseTheData

here's the deal.

这是交易。

For my project I have to serialize and deserialize a random tree using Java and XStream. My teacher made the Tree/RandomTree algorithms, so I don't have to worry about that. What I don't know how to do is this: I am using FileInputStream to read/write the xml file that I serialized and deserialized, but when I deserialize, I do not know the method used to read the file. After I read the file I should be able to convert it from XML and then print it out as a string. Here's what I have so far. (I imported everything correctly, just didn't add it to my code segment).

对于我的项目，我必须使用 Java 和 XStream 序列化和反序列化随机树。我的老师制作了 Tree/RandomTree 算法，所以我不必担心。我不知道该怎么做的是：我正在使用 FileInputStream 读取/写入我序列化和反序列化的 xml 文件，但是当我反序列化时，我不知道用于读取文件的方法。阅读文件后，我应该能够将其从 XML 转换，然后将其打印为字符串。这是我到目前为止所拥有的。（我正确导入了所有内容，只是没有将其添加到我的代码段中）。

FileInputStream fin;        

try
{
    // Open an input stream
    fin = new FileInputStream ("/Users/Pat/programs/randomtree.xml");

    //I don't know what to put below this, to read FileInpuStream object fin

    String dexml = (String)xstream.fromXML(fin);

    System.out.println(dexml);

    // Close our input stream
    fin.close();    


    System.out.println(dexml);

    // Close our input stream
    fin.close();        
}
// Catches any error conditions
catch (IOException e)
{
    System.err.println ("Unable to read from file");
    System.exit(-1);
}

---

---

Edit:Hey guys, thanks for the help, I figured it out; I don't think I have to print it as a string, I just needed to make a benchmarking framework to time it and such, but thanks again!

编辑：嘿伙计们，感谢您的帮助，我想通了；我不认为我必须将它打印为字符串，我只需要制作一个基准测试框架来计时等等，但再次感谢！

回答by Marc Novakowski

The xstream.fromXML()method will do the reading from the input stream for you. I think the problem is that you are casting the return value from xstream.fromXML(fin)into a String when it should be cast to the type of object you originally serialized (RandomTreeI assume). So the code would look like this:

该xstream.fromXML()方法将为您读取输入流。我认为问题在于，当返回值xstream.fromXML(fin)应该转换为最初序列化的对象类型时，您将返回值转换为 String（RandomTree我假设）。所以代码看起来像这样：

RandomTree tree = (RandomTree)xstream.fromXML(fin);

EDIT: after clarification in comments, the author's goal is to first read into a String so the XML contents can be printed before deserialization. With that goal in mind, I recommend taking a look at the IOUtils library mentioned in this thread

编辑：在评论中澄清之后，作者的目标是首先读入一个字符串，以便在反序列化之前可以打印 XML 内容。考虑到这一目标，我建议查看此线程中提到的 IOUtils 库

回答by Cambium

From what I understand from http://x-stream.github.io/tutorial.html(I've never worked with XStream before), you need to define your types first. Casting to String is definitely wrong, you probably want a customized type (depending on what's inside your random XML), then you need to map the XML tags to your members:

从我从http://x-stream.github.io/tutorial.html了解到的（我以前从未使用过 XStream），您需要先定义您的类型。强制转换为 String 绝对是错误的，您可能需要自定义类型（取决于您的随机 XML 中的内容），然后您需要将 XML 标签映射到您的成员：

e.g.

例如

xstream.alias("person", Person.class);
xstream.alias("phonenumber", PhoneNumber.class);

meaning that it maps the "person" tag inside your XML to your Person class.

这意味着它将 XML 中的“person”标签映射到 Person 类。

To derserialize, you can do:

要反序列化，您可以执行以下操作：

RandomTree myRandomTree = (RandomTree)xstream.fromXML( xml );

Also, you are closing your stream twice, and you probably want to do it in a finally block :)

此外，您要关闭流两次，并且您可能希望在 finally 块中执行此操作 :)

edit: Having read your comment above...

编辑：阅读您上面的评论...

Your task involves two steps:

您的任务包括两个步骤：

1. Deserialization
2. Serialization

1. 反序列化
2. 序列化

In order to serialize your object, you must deserialize it first from your input file.

为了序列化你的对象，你必须首先从你的输入文件中反序列化它。

To output your Object as String, simply do

要将您的对象输出为字符串，只需执行

String xml = xstream.toXML( myRandomTree );