java string乱码

String csn = Charset.defaultCharset().name();
try {
    // use charset name decode() variant which provides caching.
    return decode(csn, ba, off, len);
} catch (UnsupportedEncodingException x) {
    warnUnsupportedCharset(csn);
}
try {
    return decode("ISO-8859-1", ba, off, len);
} catch (UnsupportedEncodingException x) {
    // If this code is hit during VM initialization, MessageUtils is
    // the only way we will be able to get any kind of error message.
    MessageUtils.err("ISO-8859-1 charset not available: " +
        x.toString());
    // If we can not find ISO-8859-1 (a required encoding) then things
    // are seriously wrong with the installation.
    System.exit(1);
    return null;
}
System.getProperty("file.encoding") //查看系统默认编码方式

System.out.println(str);
String str1 = new String(str.getBytes("ISO-8859-1"), "utf-8");
System.out.println(str1);
String str2 = new String(str.getBytes("gb2312"), "utf-8");
System.out.println(str2);
String str3 = new String(str.getBytes("gbk"), "utf-8");
System.out.println(str3);

String decodeStr=null;
decodeStr = URLDecoder.decode(url, "utf-8");