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本文主要研究一下rocketmq的RollingFileAppender

RollingFileAppender

org/apache/rocketmq/logging/inner/LoggingBuilder.java

public static class RollingFileAppender extends FileAppender {        protected long maxFileSize = 10 * 1024 * 1024;        protected int maxBackupIndex = 1;        private long nextRollover = 0;        public RollingFileAppender() {            super();        }        public int getMaxBackupIndex() {            return maxBackupIndex;        }        public long getMaximumFileSize() {            return maxFileSize;        }        //......        public synchronized void setFile(String fileName, boolean append, boolean bufferedIO, int bufferSize)            throws IOException {            super.setFile(fileName, append, this.bufferedIO, this.bufferSize);            if (append) {                File f = new File(fileName);                ((CountingQuietWriter) qw).setCount(f.length());            }        }        public void setMaxBackupIndex(int maxBackups) {            this.maxBackupIndex = maxBackups;        }        public void setMaximumFileSize(long maxFileSize) {            this.maxFileSize = maxFileSize;        }        protected void setQWForFiles(Writer writer) {            this.qw = new CountingQuietWriter(writer, this);        }        protected void subAppend(LoggingEvent event) {            super.subAppend(event);            if (fileName != null && qw != null) {                long size = ((CountingQuietWriter) qw).getCount();                if (size >= maxFileSize && size >= nextRollover) {                    rollOver();                }            }        }        protected class CountingQuietWriter extends QuietWriter {            protected long count;            public CountingQuietWriter(Writer writer, Appender appender) {                super(writer, appender);            }            public void write(String string) {                try {                    out.write(string);                    count += string.length();                } catch (IOException e) {                    appender.handleError("Write failure.", e, Appender.CODE_WRITE_FAILURE);                }            }            public long getCount() {                return count;            }            public void setCount(long count) {                this.count = count;            }        }    }

• 这里重写了subAppend方法，调用父类subAppend方法之后，判断是否需要rollOver
• 这里定义了maxFileSize，即单个文件的大小，然后还定义了nextRollover索引
• 这里使用的是CountingQuietWriter，里头有个count来累积计算字符串的长度

RollingFileAppender.rollOver

org/apache/rocketmq/logging/inner/LoggingBuilder.java

public void rollOver() {            File target;            File file;            if (qw != null) {                long size = ((CountingQuietWriter) qw).getCount();                SysLogger.debug("rolling over count=" + size);                nextRollover = size + maxFileSize;            }            SysLogger.debug("maxBackupIndex=" + maxBackupIndex);            boolean renameSucceeded = true;            if (maxBackupIndex > 0) {                file = new File(fileName + '.' + maxBackupIndex);                if (file.exists()) {                    renameSucceeded = file.delete();                }                for (int i = maxBackupIndex - 1; i >= 1 && renameSucceeded; i--) {                    file = new File(fileName + "." + i);                    if (file.exists()) {                        target = new File(fileName + '.' + (i + 1));                        SysLogger.debug("Renaming file " + file + " to " + target);                        renameSucceeded = file.renameTo(target);                    }                }                if (renameSucceeded) {                    target = new File(fileName + "." + 1);                    this.closeFile(); // keep windows happy.                    file = new File(fileName);                    SysLogger.debug("Renaming file " + file + " to " + target);                    renameSucceeded = file.renameTo(target);                    if (!renameSucceeded) {                        try {                            this.setFile(fileName, true, bufferedIO, bufferSize);                        } catch (IOException e) {                            if (e instanceof InterruptedIOException) {                                Thread.currentThread().interrupt();                            }                            SysLogger.error("setFile(" + fileName + ", true) call failed.", e);                        }                    }                }            }            if (renameSucceeded) {                try {                    this.setFile(fileName, false, bufferedIO, bufferSize);                    nextRollover = 0;                } catch (IOException e) {                    if (e instanceof InterruptedIOException) {                        Thread.currentThread().interrupt();                    }                    SysLogger.error("setFile(" + fileName + ", false) call failed.", e);                }            }        }

• 这个方法首先更新nextRollover的值，然后根据maxBackupIndex来递增重命名文件，然后再把现有的文件重名为为.1后缀
• 重命名成功之后，再对新的文件进行setFile相关设置，关联writer，写入header

小结

RollingFileAppender在每次append的时候，都会先append数据，然后再判断是否超出文件大小限制，超出了再执行rollOver操作，对既有文件进行重命名，然后重新生成新的文件。注意这里没有进行同步操作，因此需要最外层调用的方法有同步并发控制。

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