如何在不覆盖整个文件的情况下覆盖 .properties 中的一个属性? [英] How to overwrite one property in .properties without overwriting the whole file?

问题描述

基本上，我必须通过 Java 应用程序覆盖 .properties 文件中的某个属性，但是当我使用 Properties.setProperty() 和 Properties.Store() 时，它会覆盖整个文件，而不仅仅是那个属性.

Basically, I have to overwrite a certain property in a .properties file through a Java app, but when I use Properties.setProperty() and Properties.Store() it overwrites the whole file rather than just that one property.

我已经尝试使用 append = true 构建 FileOutputStream，但它会添加另一个属性并且不会删除/覆盖现有属性.

I've tried constructing the FileOutputStream with append = true, but with that it adds another property and doesn't delete/overwrite the existing property.

我该如何编码，以便设置一个属性覆盖该特定属性，而不覆盖整个文件?

How can I code it so that setting one property overwrites that specific property, without overwriting the whole file?

我尝试读取文件并添加到其中.这是我更新的代码:

I tried reading the file and adding to it. Here's my updated code:

FileOutputStream out = new FileOutputStream("file.properties");
FileInputStream in = new FileInputStream("file.properties");
Properties props = new Properties();

props.load(in);
in.close();

props.setProperty("somekey", "somevalue");
props.store(out, null);
out.close();

推荐答案

Properties API 不提供任何用于在属性文件中添加/替换/删除属性的方法.API 支持的模型是从文件加载所有属性，对内存中的 Properties 对象进行更改，然后将所有属性存储到一个文件(相同的或不同的).

The Properties API doesn't provide any methods for adding/replacing/removing a property in the properties file. The model that the API supports is to load all of the properties from a file, make changes to the in-memory Properties object, and then store all of the properties to a file (the same one or a different one).

但是 Properties API 在这方面并不罕见.实际上，在不重写整个文件的情况下很难实现文本文件的就地更新.这种困难是现代操作系统实现文件/文件系统方式的直接后果.

But the Properties API is not unusual in the respect. In reality, in-place updating of a text file is difficult to implement without rewriting the entire file. This difficulty is a direct consequence of the way that files / file systems are implemented by a modern operating system.

如果您确实需要进行增量更新，那么您需要使用某种数据库来保存属性，而不是.properties"文件.

If you really need to do incremental updates, then you need to use some kind of database to hold the properties, not a ".properties" file.

其他答案以各种形式提出了以下方法:

Other Answers have suggested the following approach in various guises:

1. 将文件中的属性加载到 Properties 对象中.
2. 更新 Properties 对象.
3. 将 Properties 对象保存在现有文件之上.

1. Load properties from file into Properties object.
2. Update Properties object.
3. Save Properties object on top of existing file.

这适用于某些用例.然而，加载/保存可能会重新排序属性，删除嵌入的注释和空白.这些事情可能很重要¹.

This works for some use-cases. However the load / save is liable to reorder the properties, remove embedded comments and white space. These things may matter¹.

另一点是这涉及重写整个属性文件，OP 明确试图避免这种情况.

The other point is that this involves rewriting the entire properties file, which the OP is explicitly trying to avoid.

^{1 - 如果 API 是按照设计者的意图使用的，属性顺序、嵌入的注释等都无关紧要.但是让我们假设 OP 这样做是出于务实的原因".}

^{1 - If the API is used as the designers intended, property order, embedded comments, and so on wouldn't matter. But lets assume that the OP is doing this for "pragmatic reasons".}

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