1. Overview

1.概述

In this tutorial, we’ll learn and understand the FileWriter class present in the java.io package.

在本教程中，我们将学习并理解存在于java.io包中的FileWriter类。

2. FileWriter

2.FileWriter

FileWriter is a specialized OutputStreamWriter for writing character files. It doesn’t expose any new operations but works with the operations inherited from the OutputStreamWriter and Writer classes.

FileWriter是一个专门的OutputStreamWriter用于编写字符文件。它没有暴露任何新的操作，而是与从OutputStreamWriter和Writer类继承的操作一起工作。

Until Java 11, the FileWriter worked with the default character encoding and default byte buffer size. However, Java 11 introduced four new constructors that accept a Charset, thereby allowing user-specified Charset. Unfortunately, we still cannot modify the byte buffer size, and it’s set to 8192.

在 Java 11 之前，FileWriter 使用默认的字符编码和默认的字节缓冲区大小。然而，Java 11 引入了四个新的构造函数，接受Charset，从而允许用户指定Charset。不幸的是，我们仍然不能修改字节缓冲区的大小，它被设置为8192。

2.1. Instantiating the FileWriter

2.1.实例化FileWriter

There are five constructors in the FileWriter class if we’re using a Java version before Java 11.

如果我们使用Java 11之前的Java版本，FileWriter类中有五个构造函数。

Let’s have a glance at various constructors:

让我们看一下各种构造函数。

public FileWriter(String fileName) throws IOException {
    super(new FileOutputStream(fileName));
}

public FileWriter(String fileName, boolean append) throws IOException {
    super(new FileOutputStream(fileName, append));
}

public FileWriter(File file) throws IOException {
    super(new FileOutputStream(file));
}

public FileWriter(File file, boolean append) throws IOException {
    super(new FileOutputStream(file, append));
}

public FileWriter(FileDescriptor fd) {
    super(new FileOutputStream(fd));
}

Java 11 introduced four additional constructors:

Java 11引入了四个额外的构造函数。

public FileWriter(String fileName, Charset charset) throws IOException {
    super(new FileOutputStream(fileName), charset);
}

public FileWriter(String fileName, Charset charset, boolean append) throws IOException {
    super(new FileOutputStream(fileName, append), charset);
}

public FileWriter(File file, Charset charset) throws IOException {
    super(new FileOutputStream(file), charset);
}

public FileWriter(File file, Charset charset, boolean append) throws IOException {
    super(new FileOutputStream(file, append), charset);
}

**2.2. Writing a String to a File**

**2.2.将一个字符串写入文件**

Let’s now use one of the FileWriter constructors to create an instance of FileWriter and then write to a file:

现在让我们使用其中一个FileWriter构造函数来创建一个FileWriter的实例，然后写到一个文件。

try (FileWriter fileWriter = new FileWriter("src/test/resources/FileWriterTest.txt")) {
    fileWriter.write("Hello Folks!");
}

We’ve used the single argument constructor of the FileWriter that accepts a file name. We then use the write(String str) operation inherited from the Writer class. Since the FileWriter is AutoCloseable, we’ve used try-with-resources so that we don’t have to close the FileWriter explicitly.

我们使用了FileWriter的单参数构造器，它接受了一个文件名。然后我们使用从Writer类继承的write(String str)操作。由于FileWriter是AutoCloseable，我们使用了try-with-resources，这样我们就不必明确关闭FileWriter。

On executing the above code, the String will be written to the specified file:

在执行上述代码时，字符串将被写入指定文件。

Hello Folks!

The FileWriter does not guarantee whether the FileWriterTest.txt file will be available or be created. It is dependent on the underlying platform.

FileWriter并不保证FileWriterTest.txt文件是否可用或被创建。它取决于底层平台。

We must also make a note that certain platforms may allow only a single FileWriter instance to open the file. In that case, the other constructors of the FileWriter class will fail if the file involved is already open.

我们还必须注意，某些平台可能只允许一个FileWriter实例来打开文件。在这种情况下，如果所涉及的文件已经打开，FileWriter类的其他构造函数将会失败。

**2.3. Appending a String to a File**

**2.3.将一个字符串添加到一个文件**

We often need to append data to the existing contents of a file. Let’s now see an example of a FileWriter that supports appending:

我们经常需要将数据追加到一个文件的现有内容中。现在让我们看看一个支持追加的FileWriter的例子。

try (FileWriter fileWriter = new FileWriter("src/test/resources/FileWriterTest.txt", true)) {
    fileWriter.write("Hello Folks Again!");
}

As we can see, we’ve used the two-argument constructor that accepts a file name and a boolean flag append. Passing the flag append as true creates a FileWriter that allows us to append text to existing contents of a file.

正如我们所见，我们使用了双参数构造函数，它接受一个文件名和一个boolean标志append。将标志append设为true，可以创建一个FileWriter，允许我们将文本追加到文件的现有内容中。

On executing the code, we’ll have the String appended to the existing contents of the specified file:

在执行该代码时，我们将把String追加到指定文件的现有内容中。

Hello Folks!Hello Folks Again!

3. Conclusion

3.结论

In this article, we learned about the convenience class FileWriter and a couple of ways in which the FileWriter can be created. We then used it to write data to a file.

在这篇文章中，我们了解了便利类FileWriter以及创建FileWriter的几种方法。然后我们用它把数据写到了一个文件中。

As always, the complete source code for the tutorial is available over on GitHub.

一如既往，该教程的完整源代码可在GitHub上获取。