Java – Append Data to a File – Java – 将数据追加到一个文件中

1. Introduction

1.介绍

In this quick tutorial, we’ll see how we use Java to append data to the content of a file – in a few simple ways.

在这个快速教程中，我们将看到如何使用Java将数据追加到文件的内容中–有几种简单的方法。

Let’s start with how we can do this using core Java’s FileWriter.

让我们先来看看如何使用核心Java的FileWriter.来实现这一目标。

2. Using FileWriter

2.使用FileWriter

Here’s a simple test – reading an existing file, appending some text, and then making sure that got appended correctly:

这里有一个简单的测试–读取一个现有的文件，添加一些文本，然后确保这些文本被正确添加。

@Test
public void whenAppendToFileUsingFileWriter_thenCorrect()
  throws IOException {
 
    FileWriter fw = new FileWriter(fileName, true);
    BufferedWriter bw = new BufferedWriter(fw);
    bw.write("Spain");
    bw.newLine();
    bw.close();
    
    assertThat(getStringFromInputStream(
      new FileInputStream(fileName)))
      .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
}

Note that FileWriter’s constructor accepts a boolean marking if we want to append data to an existing file.

请注意，FileWriter的构造函数接受一个boolean标记，如果我们想将数据追加到一个现有的文件。

If we set it to false, then the existing content will be replaced.

如果我们将其设置为false，那么现有的内容将被替换。

3. Using FileOutputStream

3.使用FileOutputStream

Next – let’s see how we can do the same operation – using FileOutputStream:

接下来–让我们看看如何做同样的操作–使用FileOutputStream。

@Test
public void whenAppendToFileUsingFileOutputStream_thenCorrect()
 throws Exception {
 
    FileOutputStream fos = new FileOutputStream(fileName, true);
    fos.write("Spain\r\n".getBytes());
    fos.close();
    
    assertThat(StreamUtils.getStringFromInputStream(
      new FileInputStream(fileName)))
      .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
}

Similarly, the FileOutputStream constructor accepts a boolean that should be set to true to mark that we want to append data to an existing file.

同样，FileOutputStream构造函数接受一个布尔值，该布尔值应设置为true，以标记我们要将数据追加到一个现有文件中。

4. Using java.nio.file

4.使用java.nio.file

Next – we can also append content to files using functionality in java.nio.file – which was introduced in JDK 7:

接下来–我们还可以使用java.nio.file中的功能向文件追加内容–这是在JDK 7中引入的。

@Test
public void whenAppendToFileUsingFiles_thenCorrect() 
 throws IOException {
 
    String contentToAppend = "Spain\r\n";
    Files.write(
      Paths.get(fileName), 
      contentToAppend.getBytes(), 
      StandardOpenOption.APPEND);
    
    assertThat(StreamUtils.getStringFromInputStream(
      new FileInputStream(fileName)))
      .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
}

5. Using Guava

5.使用Guava

To start using Guava, we need to add its dependency to our pom.xml:

要开始使用Guava，我们需要把它的依赖性添加到我们的pom.xml中。

<dependency>
    <groupId>com.google.guava</groupId>
    <artifactId>guava</artifactId>
    <version>31.0.1-jre</version>
</dependency>

Now, let’s see how we can start using Guava to append content to an existing file:

现在，让我们看看如何开始使用Guava将内容追加到一个现有的文件。

@Test
public void whenAppendToFileUsingFileWriter_thenCorrect()
 throws IOException {
 
    File file = new File(fileName);
    CharSink chs = Files.asCharSink(
      file, Charsets.UTF_8, FileWriteMode.APPEND);
    chs.write("Spain\r\n");
	
    assertThat(StreamUtils.getStringFromInputStream(
      new FileInputStream(fileName)))
      .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
}

6. Using Apache Commons IO FileUtils

6.使用Apache Commons IO FileUtils

Finally – let’s see how we can append content to an existing file using Apache Commons IO FileUtils.

最后–让我们看看如何使用Apache Commons IO FileUtils将内容追加到一个现有的文件。

First, let’s add the Apache Commons IO dependency to our pom.xml:

首先，让我们把Apache Commons IO的依赖关系添加到我们的pom.xml。

<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.11.0</version>
</dependency>

Now, let’s see a quick example that demonstrates appending content to an existing file using FileUtils:

现在，让我们看一个快速的例子，演示如何使用FileUtils将内容追加到一个现有的文件。

@Test
public void whenAppendToFileUsingFiles_thenCorrect()
 throws IOException {
    File file = new File(fileName);
    FileUtils.writeStringToFile(
      file, "Spain\r\n", StandardCharsets.UTF_8, true);
    
    assertThat(StreamUtils.getStringFromInputStream(
      new FileInputStream(fileName)))
      .isEqualTo("UK\r\n" + "US\r\n" + "Germany\r\n" + "Spain\r\n");
}

7. Conclusion

7.结论

In this article, we’ve seen how we can append content in multiple ways.

在这篇文章中，我们已经看到我们如何以多种方式追加内容。

The full implementation of this tutorial can be found over on GitHub.

本教程的完整实现可以在GitHub上找到over。