thinking in java (二十九) ----- IO之 InputStreamReader和OutputStreamWriter

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InputStreamReader和OutputStreamWriter介绍

InputStreamReader和OutputStreamWriter是字节通往字符的桥梁,它使用指定的charset读取字节并将其解码为字符。

InputStreamReader的作用是将字节输入流转换为字符输入流,继承于Reader 

OutputStreamWriter的作用是将字节输出流转换为字符输出流,继承于WriterOutputStreamWriter

InputStreamReader和OutputStreamWriter源码

InputStreamReader源码

package java.io;

import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import sun.nio.cs.StreamDecoder;


// 将“字节输入流”转换成“字符输入流”
public class InputStreamReader extends Reader {

    private final StreamDecoder sd;

    // 根据in创建InputStreamReader,使用默认的编码
    public InputStreamReader(InputStream in) {
        super(in);
        try {
            sd = StreamDecoder.forInputStreamReader(in, this, (String)null); // ## check lock object
        } catch (UnsupportedEncodingException e) {
            // The default encoding should always be available
            throw new Error(e);
        }
    }

    // 根据in创建InputStreamReader,使用编码charsetName(编码名)
    public InputStreamReader(InputStream in, String charsetName)
        throws UnsupportedEncodingException
    {
        super(in);
        if (charsetName == null)
            throw new NullPointerException("charsetName");
        sd = StreamDecoder.forInputStreamReader(in, this, charsetName);
    }

    // 根据in创建InputStreamReader,使用编码cs
    public InputStreamReader(InputStream in, Charset cs) {
        super(in);
        if (cs == null)
            throw new NullPointerException("charset");
        sd = StreamDecoder.forInputStreamReader(in, this, cs);
    }

    // 根据in创建InputStreamReader,使用解码器dec
    public InputStreamReader(InputStream in, CharsetDecoder dec) {
        super(in);
        if (dec == null)
            throw new NullPointerException("charset decoder");
        sd = StreamDecoder.forInputStreamReader(in, this, dec);
    }

    // 获取解码器
    public String getEncoding() {
        return sd.getEncoding();
    }

    // 读取并返回一个字符
    public int read() throws IOException {
        return sd.read();
    }

    // 将InputStreamReader中的数据写入cbuf中,从cbuf的offset位置开始写入,写入长度是length
    public int read(char cbuf[], int offset, int length) throws IOException {
        return sd.read(cbuf, offset, length);
    }

    // 能否从InputStreamReader中读取数据
    public boolean ready() throws IOException {
        return sd.ready();
    }

    // 关闭InputStreamReader
    public void close() throws IOException {
        sd.close();
    }
}

OutputStreamWriter 

package java.io;

import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import sun.nio.cs.StreamEncoder;

// 将“字节输出流”转换成“字符输出流”
public class OutputStreamWriter extends Writer {

    private final StreamEncoder se;

    // 根据out创建OutputStreamWriter,使用编码charsetName(编码名)
    public OutputStreamWriter(OutputStream out, String charsetName)
        throws UnsupportedEncodingException
    {
        super(out);
        if (charsetName == null)
            throw new NullPointerException("charsetName");
        se = StreamEncoder.forOutputStreamWriter(out, this, charsetName);
    }

    // 根据out创建OutputStreamWriter,使用默认的编码
    public OutputStreamWriter(OutputStream out) {
        super(out);
        try {
            se = StreamEncoder.forOutputStreamWriter(out, this, (String)null);
        } catch (UnsupportedEncodingException e) {
            throw new Error(e);
        }
    }

    // 根据out创建OutputStreamWriter,使用编码cs
    public OutputStreamWriter(OutputStream out, Charset cs) {
        super(out);
        if (cs == null)
            throw new NullPointerException("charset");
        se = StreamEncoder.forOutputStreamWriter(out, this, cs);
    }

    // 根据out创建OutputStreamWriter,使用编码器enc
    public OutputStreamWriter(OutputStream out, CharsetEncoder enc) {
        super(out);
        if (enc == null)
            throw new NullPointerException("charset encoder");
        se = StreamEncoder.forOutputStreamWriter(out, this, enc);
    }java io系列01之 "目录"

    // 获取编码器enc
    public String getEncoding() {
        return se.getEncoding();
    }

    // 刷新缓冲区
    void flushBuffer() throws IOException {
        se.flushBuffer();
    }

    // 将单个字符写入到OutputStreamWriter中
    public void write(int c) throws IOException {
        se.write(c);
    }

    // 将字符数组cbuf从off开始的数据写入到OutputStreamWriter中,写入长度是len
    public void write(char cbuf[], int off, int len) throws IOException {
        se.write(cbuf, off, len);
    }

    // 将字符串str从off开始的数据写入到OutputStreamWriter中,写入长度是len
    public void write(String str, int off, int len) throws IOException {
        se.write(str, off, len);
    }java io系列01之 "目录"

    // 刷新“输出流”
    // 它与flushBuffer()的区别是:flushBuffer()只会刷新缓冲,而flush()是刷新流,flush()包括了flushBuffer。
    public void flush() throws IOException {
        se.flush();
    }

    // 关闭“输出流”
    public void close() throws IOException {
        se.close();
    }
}

作用就是讲字节流转换为字符流,他们的原理是,我们创建字符流的时候,需要指定字节流,和字符编码方式。

示例程序

package test;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.io.InputStreamReader;
import java.io.IOException;

/**
 * InputStreamReader 和 OutputStreamWriter 测试程序
 *
 * @author skywang
 */
public class StreamConverter {

    private static final String FileName = "file.txt";
    private static final String CharsetName = "utf-8";
    //private static final String CharsetName = "gb2312";

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

    /**
     * OutputStreamWriter 演示函数
     *
     */
    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OutputStreamWriter: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。
            OutputStreamWriter out1 = new OutputStreamWriter(new FileOutputStream(file), CharsetName);
            // 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);
            InputStreamReader in1 = new InputStreamReader(new FileInputStream(file), CharsetName);

            // 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
结果说明
(01) testWrite() 的作用是将“内容写入到输出流”。写入的时候,会将写入的内容转换utf-8编码并写入。
(02) testRead() 的作用是将“内容读取到输入流”。读取的时候,会将内容转换成utf-8的内容转换成字节并读出来。
生成的文件utf-8的file.txt的16进制效果图如下:

将StreamConverter.java中的CharsetName修改为"gb2312"。运行程序,生产的file.txt的16进制效果图如下:

原文:http://www.cnblogs.com/skywang12345/p/io_21.html

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