Java FileWriter 示例

2 年 ago
文, 翔
5 minutes

Java的FileWriter

  • Java FileWriter class is a part of java.io package.
  • FileWriter is a sub class of java.io.OutputStreamWriter class.
  • FileWriter is meant for writing streams of characters.
  • FileWriter is used to write to character files. Its write() methods allow you to write character(s) or strings to a file.
  • FileWriters are usually wrapped by higher-level Writer objects, such as BufferedWriter or PrintWriter, which provide better performance and higher-level, more flexible methods to write data.
Java FileWriter

FileWriter 构造函数

    FileWriter(File file): 使用指定的File对象创建一个FileWriter对象。如果文件存在但是是一个目录而不是一个普通文件，或者文件不存在但是无法创建，或者无法以任何其他原因打开文件，则抛出一个IOException。

    FileWriter(File file, boolean append): 使用指定的File对象创建一个FileWriter对象。如果第二个参数为true，则会将字节写入文件的末尾而不是开头。如果文件存在但是是一个目录而不是一个普通文件，或者文件不存在但是无法创建，或者无法以任何其他原因打开文件，则抛出一个IOException。

    FileWriter(FileDescriptor fd): 创建一个与指定文件描述符关联的FileWriter对象。

    FileWriter(String fileName): 使用指定的文件名创建一个FileWriter对象。如果文件存在但是是一个目录而不是一个普通文件，或者文件不存在但是无法创建，或者无法以任何其他原因打开文件，则抛出一个IOException。

    FileWriter(String fileName, boolean append): 使用指定的文件名创建一个FileWriter对象，并使用一个布尔值指示是否追加写入的数据。如果第二个参数为true，则数据将被写入文件的末尾而不是开头。如果文件存在但是是一个目录而不是一个普通文件，或者文件不存在但是无法创建，或者无法以任何其他原因打开文件，则抛出一个IOException。

Java FileWriter示例

Java FileWriter示例展示了如何使用FileWriter类进行文件写入。

FileWriter继承了java.io.OutputStreamWriter和java.io.Writer类的方法。我们来看一下下面的一些方法和示例。

写 int c

这个方法写入一个由整数c指定的单个字符。

package com.Olivia.io.filewriter;

import java.io.FileWriter;
import java.io.IOException;

/**
 * Java write file using FileWriter write method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteIntExample {

	public static void main(String[] args) {
		FileWriter fileWriter = null;
		try {
			fileWriter = new FileWriter("D:/data/file.txt");
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(65);
			fileWriter.write(66);
			fileWriter.write(67);
		} catch (Exception e) {
			e.printStackTrace();
		}finally {
			try {
				if (fileWriter != null) {
					fileWriter.flush();
					fileWriter.close();					
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
}
Java FileWriter Example 
package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write method using try with resource
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteIntTryWithResource {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(65);
			fileWriter.write(66);
			fileWriter.write(67);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

注意：上述程序中，fileWriter.write(65)会将字符A写入文件，因为65是字符A的十进制值，所以整数65会被转换成字符A，其他字符同理。

写入 String str, int off, int len

这种方法从整数off开始，将字符串str的一部分写入到整数len中。

  • str: String to be written
  • off: Offset from which to start reading characters
  • len: Number of characters to be written

如果len参数的值为负数，则不会写入任何字符。

package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(String  s,  int  off,  int  len) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteStringExample {

	public static void main(String[] args) {
		String data = "This is FileWriter Example.";
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(data, 8, 10);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}
FileWriter write example

将字符数组cbuf的从off位置开始的长度为len的部分写入。

该方法将字符数组char[] cbuf中从off位置开始，长度为len的一部分写入。

  • cbuf: A character array
  • off: Offset from which to start reading characters
  • len : Number of characters to write
package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(char[] cbuf,  int  off,  int  len) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteCharArray {

	public static void main(String[] args) {
		char[] data = "This is FileWriter Example.".toCharArray();
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.OutputStreamWriter 
			fileWriter.write(data, 8, 10);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

请将字符数组cbuf写入。

这个方法将由cbuf指定的字符数组写入。

package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(char[] cbuf) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteCharArrayExample {

	public static void main(String[] args) {
		char[] data = "This is FileWriter Example.".toCharArray();
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write(data);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

写 String str

这种方法将一个字符串值写入由str指定的文件中。

package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter write(String  str) method
 * 
 * @author pankaj
 *
 */
public class FileWriterWriteString {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

添加字符c

将指定字符追加到此写入器中，其中c是要追加的16位字符。

package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file using FileWriter append(char c) method
 * 
 * @author pankaj
 *
 */
public class FileWriterAppendCharacter {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
			fileWriter.append('C');
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

执行flush()

这个方法清空了流。当调用flush()方法时，它立即将数据写入输出文件。

package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file with FileWriter flush() method
 * 
 * @author pankaj
 *
 */
public class FileWriterFlushExample {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
			//inherited method from java.io.OutputStreamWriter
			fileWriter.flush();
			
			fileWriter.write(" Tutorials");
			fileWriter.flush();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

close()

在关闭流之前，该方法会刷新流。一旦流被关闭，调用write()或flush()方法将导致抛出IOException。关闭已关闭的流不会产生任何效果。

package com.Olivia.io.filewriter;

import java.io.FileWriter;

/**
 * Java write file with FileWriter close() method
 * 
 * @author pankaj
 *
 */
public class FileWriterCloseExample {

	public static void main(String[] args) {
		try(FileWriter fileWriter = new FileWriter("D:/data/file.txt")) {
			//inherited method from java.io.Writer 
			fileWriter.write("JournalDev");
			//inherited method from java.io.OutputStreamWriter
			fileWriter.close();;
			
			fileWriter.write(" Tutorials");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

输出：

java.io.IOException: Stream closed
	at sun.nio.cs.StreamEncoder.ensureOpen(Unknown Source)
	at sun.nio.cs.StreamEncoder.write(Unknown Source)
	at sun.nio.cs.StreamEncoder.write(Unknown Source)
	at java.io.OutputStreamWriter.write(Unknown Source)
	at java.io.Writer.write(Unknown Source)
	at com.Olivia.examples.FileWriterCloseExample.main(FileWriterCloseExample.java:20)

FileWriter 和 FileOutputStream 的比较

  • FileWriter is meant for writing streams of characters while FileOutputStream is used for writing streams of raw bytes.
  • FileWriter deal with 16-bit characters while FileOutputStream deals with 8-bit bytes.
  • FileWriter can handle Unicode strings while FileOutputStream writes bytes to a file and do not accepts characters or strings hence it needs to wrapped up by OutputStreamWriter to accept strings.

还要检查Java写文件以了解如何在Java中编写文件。Java FileWriter就是这些，希望没有漏掉任何重要的内容。

你可以从我们的GitHub存储库下载所有示例代码。

参考: API文档

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