convertencoding.java

java小例程3。多个小例程

import java.io.*;

public class ConvertEncoding {
    public static void main(String[] args) {
        String from = null, to = null;
        String infile = null, outfile = null;
        for(int i = 0; i <args.length; i++) { // 处理命令行参数.
            if (i == args.length-1) usage();   .
            if (args[i].equals("-from")) from = args[++i];
            else if (args[i].equals("-to")) to = args[++i];
            else if (args[i].equals("-in")) infile = args[++i];
            else if (args[i].equals("-out")) outfile = args[++i];
            else usage();
        }

        try { convert(infile, outfile, from, to); }  // 开始转换.
        catch (Exception e) {                // 处理例外.
             System.exit(1);
        }
    }

    public static void usage() {
        System.err.println("Usage: java ConvertEncoding <options>\n" +
			   "Options:\n\t-from <encoding>\n\t" +
			   "-to <encoding>\n\t" +
			   "-in <file>\n\t-out <file>");
        System.exit(1);
    }

    public static void convert(String infile, String outfile,
			       String from, String to)
              throws IOException, UnsupportedEncodingException
    {
        // Set up byte streams.
        InputStream in;
        if (infile != null) in = new FileInputStream(infile);
        else in = System.in;
        OutputStream out;
        if (outfile != null) out = new FileOutputStream(outfile);
        else out = System.out;

        // 设置缺省的编码方式.
        if (from == null) from = System.getProperty("file.encoding");
        if (to == null) to = System.getProperty("file.encoding");

        // 建立用于读写的字符流.
        Reader r = new BufferedReader(new InputStreamReader(in, from));
        Writer w = new BufferedWriter(new OutputStreamWriter(out, to));

/** 把字符从输入Copy到输出. InputStreamReader
* 把字符从原始编码方式转为Unicode 
        * OutputStreamWriter 则把字符从Unicode编码转换为指定的输出编码方式.
        * 不能用指定输出编码方式编码的字符输出为'?'
        **/
        char[] buffer = new char[4096];
        int len;
        while((len = r.read(buffer)) != -1) .
            w.write(buffer, 0, len);     .
        r.close();                    .
        w.close();                   .
    }
}