protected void closeWriter() {
        if (this.out != null) {
            try {
                this.out.close();
            }
            catch (final IOException e) {
                // There is do need to invoke an error handler at this late
                // stage.
                LogLog.error("Could not close " + this.out, e);
            }
        }
    }
Close the underlying {@link java.io.Writer}.
metamorphosis-client-extension/src/main/java/com/taobao/metamorphosis/client/extension/log4j/StreamAppender.java