1. Overview

1.概述

In this quick tutorial, we’re going to show how to convert a File to an InputStream — first using plain Java and then Guava and the Apache Commons IO library.

在这个快速教程中，我们将展示如何将文件转换为InputStream –首先使用普通Java，然后是Guava和Apache Commons IO库。

This article is part of the Java – Back to Basics series here on Baeldung.

本文是Java – Back to Basics系列的一部分，在Baeldung这里。

2. Convert Using Java

2.使用Java进行转换

We can use the IO package of Java to convert a File to different InputStreams.

我们可以使用Java的IO包来将一个文件转换为不同的InputStreams。。

2.1. FileInputStream

2.1.FileInputStream

Let’s start with the first and simplest one — using a FileInputStream:

让我们从第一个也是最简单的一个开始–使用一个FileInputStream。

@Test
public void givenUsingPlainJava_whenConvertingFileToInputStream_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/main/resources/sample.txt");
    InputStream targetStream = new FileInputStream(initialFile);
}

2.2. DataInputStream

2.2.DataInputStream

Let’s look at another method, where we can use DataInputStream to read binary or primitive data from a file:

让我们看看另一种方法，我们可以使用DataInputStream来从文件中读取二进制或原始数据。

@Test
public final void givenUsingPlainJava_whenConvertingFileToDataInputStream_thenCorrect() 
  throws IOException {
      final File initialFile = new File("src/test/resources/sample.txt");
      final InputStream targetStream = 
        new DataInputStream(new FileInputStream(initialFile));
}

2.3. SequenceInputStream

2.3.序列输入流

Finally, let’s also look at how to use SequenceInputStream to concatenate the input stream of two files to a single InputStream:

最后，我们也来看看如何使用SequenceInputStream将两个文件的输入流连接成一个InputStream。

@Test
public final void givenUsingPlainJava_whenConvertingFileToSequenceInputStream_thenCorrect() 
  throws IOException {
      final File initialFile = new File("src/test/resources/sample.txt");
      final File anotherFile = new File("src/test/resources/anothersample.txt");
      final InputStream targetStream = new FileInputStream(initialFile);
      final InputStream anotherTargetStream = new FileInputStream(anotherFile);
    
      InputStream sequenceTargetStream = 
        new SequenceInputStream(targetStream, anotherTargetStream);
}

Note that we’re not closing the resulting stream in these examples for legibility.

请注意，在这些例子中，我们没有关闭产生的流，以保证可读性。

3. Convert Using Guava

3.使用Guava进行转换

Next, let’s see the Guava solution, using an intermediary ByteSource:

接下来，让我们看看Guava的解决方案，使用一个中间的ByteSource。

@Test
public void givenUsingGuava_whenConvertingFileToInputStream_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/main/resources/sample.txt");
    InputStream targetStream = Files.asByteSource(initialFile).openStream();
}

4. Convert Using Commons IO

4.使用Commons IO进行转换

Finally, let’s look at a solution using Apache Commons IO:

最后，让我们看一下使用Apache Commons IO的解决方案。

@Test
public void givenUsingCommonsIO_whenConvertingFileToInputStream_thenCorrect() 
  throws IOException {
    File initialFile = new File("src/main/resources/sample.txt");
    InputStream targetStream = FileUtils.openInputStream(initialFile);
}

And there we have it. Three simple and clean solutions for opening a stream from a Java file.

就这样，我们拥有了它。从Java文件中打开一个流的三个简单而干净的解决方案。

5. Conclusion

5.结论

In this article, we explored various ways to convert a File to InputStream by using different libraries.

在这篇文章中，我们探讨了通过使用不同的库将文件转换为InputStream的各种方法。

The implementation of all these examples and code snippets can be found over on GitHub. This is a Maven-based project, so it should be easy to import and run as it is.

所有这些例子和代码片断的实现都可以在GitHub上找到over。这是一个基于Maven的项目，所以应该很容易导入并按原样运行。