字符流Reader、Writer，字符转换流 OutputStreamWriter、InputStreamReader

Reader、Writer是所有字符流的超类。

Writer类方法

void write(String str)

void write(char[] cbuf, int off, int len);

void flush()

void close

OutputStreamWriter构造方法字符编码默认为系统编码，可以不写

FileWriter的append默认为false，可以不写。另一个构造(File file, boolean append)

        Writer out = new FileWriter("E:/a.txt", true);
        
        OutputStream ops = new FileOutputStream("E:/a.txt", true);
        Writer out = new OutputStreamWriter(ops, "GBK");  // 默认系统编码，可以不写

Reader类

int read(char[] cbuf)

InputStreamReader与OutputStreamWriter类似

FileReader 与 FileWriter类似’

        Reader in = new FileReader("E:/gbk.txt");
        
        InputStream inStream = new FileInputStream("E/gbk.txt");
        Reader in = new InputStreamReader(inStream, "gbk");

 BufferedReader,BufferedWriter使用与BufferedOutputStream, BufferedInputStream用法相同

这段代码对比了4种方式进行字符流复制速度。

    public static void main(String[] args) throws IOException, InterruptedException {

        /*文件  114M 
         * 逐字符读，无缓冲    10252
         * 逐字符读，有缓冲    7730
         * 1024字符，无缓冲   3645
         * 1024字符   有缓冲    3578
         */
        long b = System.currentTimeMillis();
        copy_4();
        long a = System.currentTimeMillis();
        System.out.println(a-b);
    }
    
    public static void copy_1() throws IOException{
        Reader r = new FileReader("E:/test.pdf");
        BufferedReader in = new BufferedReader(r);
        
        Writer w = new FileWriter("E:/copy.pdf");
        BufferedWriter out = new BufferedWriter(w);
        
        int len;
        while((len = in.read()) != -1)
        {
            out.write(len);
        }
        
        in.close();
        out.close();
    }
    
    public static void copy_2() throws IOException{
        Reader in = new FileReader("E:/test.pdf");
        Writer out = new FileWriter("E:/copy.pdf");
        int len;
        while((len = in.read()) != -1)
        {
            out.write(len);
        }
        in.close();
        out.close();
    }
    public static void copy_3() throws IOException{
        Reader in = new FileReader("E:/test.pdf");
        Writer out = new FileWriter("E:/copy.pdf");
        int len;
        char[] cbuf = new char[1024];
        while((len = in.read(cbuf)) != -1)
        {
            out.write(cbuf,0,len);
            out.flush();
        }
        in.close();
        out.close();
    }
    
    public static void copy_4() throws IOException{
        Reader r = new FileReader("E:/test.pdf");
        BufferedReader in = new BufferedReader(r);
        
        Writer w = new FileWriter("E:/copy.pdf");
        BufferedWriter out = new BufferedWriter(w);
        
        int len;
        char[] cbuf = new char[1024];
        while((len = in.read(cbuf)) != -1)
        {
            out.write(cbuf,0,len);
            out.flush();
        }
        in.close();
        out.close();
    }