JavaIO<15>FileReader和FileWriter源码分析及介绍使用

FileReader 是用于读取字符流的类，它继承于InputStreamReader。要读取原始字节流，请考虑使用 FileInputStream。
FileWriter 是用于写入字符流的类，它继承于OutputStreamWriter。要写入原始字节流，请考虑使用 FileOutputStream。 
FileReader和FileWriter源码分析

1. FileReader 源码(基于jdk1.7.40)

package java.io;  
 
public class FileReader extends InputStreamReader {  
 
    public FileReader(String fileName) throws FileNotFoundException {  
        super(new FileInputStream(fil java io系列21之 InputStreamReader和OutputStreamWritereName));  
    }  
 
    public FileReader(File file) throws FileNotFoundException {  
        super(new FileInputStream(file));  
    }  
 
    public FileReader(FileDescriptor fd) {  
        super(new FileInputStream(fd));  
    }  
}

从中，我们可以看出FileReader是基于InputStreamReader实现的。 
2. FileWriter 源码(基于jdk1.7.40)

package java.io;  
 
public class FileWriter extends OutputStreamWriter {  
 
    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));  
    }  
}

从中，我们可以看出FileWriter是基于OutputStreamWriter实现的。

示例程序

package org.credo.jdk.io;

import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class FileReaderWriterTest
{

	public static void main(String[] args)
	{
		testWrite();
		testRead();
	}

	private static final String FileName = "file.txt";
	private static final String CharsetName = "utf-8";

	private static void testWrite()
	{
		try
		{
			// 创建文件“file.txt”对应File对象
			File file = new File(FileName);
			// 创建FileOutputStream对应FileWriter：将字节流转换为字符流，即写入out1的数据会自动由字节转换为字符。
			FileWriter out1 = new FileWriter(file);
			// 写入10个汉字
			out1.write("字节流转为字符流示例");
			// 向“文件中”写入"0123456789"+换行符
			out1.write("0123456789\n");

			out1.close();

		} catch (IOException e)
		{
			e.printStackTrace();
		}
	}

	/**
	 * InputStreamReader 演示程序
	 */
	private static void testRead()
	{
		try
		{
			// 方法1：新建FileInputStream对象
			// 新建文件“file.txt”对应File对象
			File file = new File(FileName);
			FileReader in1 = new FileReader(file);

			// 测试read()，从中读取一个字符
			char c1 = (char) in1.read();
			System.out.println("c1=" + c1);

			// 测试skip(long byteCount)，跳过4个字符
			in1.skip(6);

			// 测试read(char[] cbuf, int off, int len)
			char[] buf = new char[10];
			in1.read(buf, 0, buf.length);
			System.out.println("buf=" + (new String(buf)));

			in1.close();
		} catch (IOException e)
		{
			e.printStackTrace();
		}
	}

}

运行结果：
c1=字
buf=流示例0123456