系统变量file.encoding对Java的运行影响有多大?(转)good

这个话题来自: Nutz的issue 361

在考虑这个issue时, 我一直倾向于使用系统变量file.encoding来改变JVM的默认编码.

今天,我想到, 这个系统变量,对JVM的影响到底有多大呢? 我使用最简单的方法看看这个变量的影响--在JDK 1.6.0_20的src.zip文件中,查找包含file.encoding字眼的文件. 共找到4个, 分别是: 先上重头戏 java.nio.Charset类:

    public static Charset defaultCharset() {
        if (defaultCharset == null) {
        synchronized (Charset.class) {
        java.security.PrivilegedAction pa =
            new GetPropertyAction("file.encoding");
        String csn = (String)AccessController.doPrivileged(pa);
        Charset cs = lookup(csn);
        if (cs != null)
            defaultCharset = cs;
                else 
            defaultCharset = forName("UTF-8");
            }
    }
    return defaultCharset;
    }

java.net.URLEncoder的静态构造方法,影响到的方法 java.net.URLEncoder.encode(String)

    static {

    dontNeedEncoding = new BitSet(256);
    int i;
    for (i = 'a'; i < = 'z'; i++) {
        dontNeedEncoding.set(i);
    }
    for (i = 'A'; i <= 'Z'; i++) {
        dontNeedEncoding.set(i);
    }
    for (i = '0'; i <= '9'; i++) {
        dontNeedEncoding.set(i);
    }
    dontNeedEncoding.set(' '); /* encoding a space to a + is done
                    * in the encode() method */
    dontNeedEncoding.set('-');
    dontNeedEncoding.set('_');
    dontNeedEncoding.set('.');
    dontNeedEncoding.set('*');

        dfltEncName = (String)AccessController.doPrivileged (
        new GetPropertyAction("file.encoding")
        );
    }

com.sun.org.apache.xml.internal.serializer.Encoding的getMimeEncoding方法(209行起)

    static String getMimeEncoding(String encoding)
    {

        if (null == encoding)
        {
            try
            {

                // Get the default system character encoding.  This may be
                // incorrect if they passed in a writer, but right now there
                // seems to be no way to get the encoding from a writer.
                encoding = System.getProperty("file.encoding", "UTF8");

                if (null != encoding)
                {

                    /*
                    * See if the mime type is equal to UTF8.  If you don't
                    * do that, then  convertJava2MimeEncoding will convert
                    * 8859_1 to "ISO-8859-1", which is not what we want,
                    * I think, and I don't think I want to alter the tables
                    * to convert everything to UTF-8.
                    */
                    String jencoding =
                        (encoding.equalsIgnoreCase("Cp1252")
                            || encoding.equalsIgnoreCase("ISO8859_1")
                            || encoding.equalsIgnoreCase("8859_1")
                            || encoding.equalsIgnoreCase("UTF8"))
                            ? DEFAULT_MIME_ENCODING
                            : convertJava2MimeEncoding(encoding);

                    encoding =
                        (null != jencoding) ? jencoding : DEFAULT_MIME_ENCODING;
                }
                else
                {
                    encoding = DEFAULT_MIME_ENCODING;
                }
            }
            catch (SecurityException se)
            {
                encoding = DEFAULT_MIME_ENCODING;
            }
        }

最后一个javax.print.DocFlavor类的静态构造方法:

    static {
    hostEncoding = 
        (String)java.security.AccessController.doPrivileged(
                  new sun.security.action.GetPropertyAction("file.encoding"));
    }

可以看到,系统变量file.encoding影响到
1. Charset.defaultCharset() Java环境中最关键的编码设置
2. URLEncoder.encode(String) Web环境中最常遇到的编码使用
3. com.sun.org.apache.xml.internal.serializer.Encoding 影响对无编码设置的xml文件的读取
4. javax.print.DocFlavor 影响打印的编码

故,影响还是很大的哦, 可以说是Java中编码的一个关键钥匙!
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