fileappender rollover_log4j appenders_appender name(2)

提供了写入刷新控制

可配置编码方式

提供了静态字符流QuitWriter,异常不会抛出，会交给ErrorHandler去处理

//默认实时刷新，效率低但可保证每次输出均可写入，设为false时，若程序崩溃，尾部log可能丢失
protected boolean immediateFlush = true;
protected String encoding;
protected QuietWriter qw;

提供了字节流->字符流的转换

log输出 官方注释说明了在log输出之前做的检查或过滤操作[检查日志级别->过滤->检查当前输出状况(Appender状态、输出流、格式是否均具备)->输出]

public void append(LoggingEvent event) {

// Reminder: the nesting of calls is:
//
//    doAppend()
//      - check threshold
//      - filter
//      - append();
//        - checkEntryConditions();
//        - subAppend();

if(!checkEntryConditions()) {
  return;
}
subAppend(event);
 }

protected void subAppend(LoggingEvent event) {
this.qw.write(this.layout.format(event));//将日志格式化后输出
//依次输出异常栈
if(layout.ignoresThrowable()) {
  String[] s = event.getThrowableStrRep();
  if (s != null) {
    int len = s.length;
    for(int i = 0; i < len; i++) {
      this.qw.write(s[i]);
      this.qw.write(Layout.LINE_SEP);
    }
  }
}
//写入刷新控制
if(shouldFlush(event)) {
  this.qw.flush();
}
}

还有一些Header、Footer的写入和输出流的关闭操作

继承了WriteAppender，将log输出到文件。这个比较简单，主要就是将父类中的输出流封装指向到文件。

protected boolean fileAppend = true;//是否覆盖
protected String fileName = null;//目标文件名
protected boolean bufferedIO = false;//是否缓冲 
protected int bufferSize = 8*1024;//默认缓冲区大小

public synchronized void setFile(String fileName, boolean append, boolean bufferedIO, int bufferSize)
                                                        throws IOException {
LogLog.debug("setFile called: "+fileName+", "+append);

// It does not make sense to have immediate flush and bufferedIO.
if(bufferedIO) {
  setImmediateFlush(false);//既然缓冲了，那意味着父类中的刷新控制为false-不进行同步刷新
}

reset();
FileOutputStream ostream = null;
try {
      ostream = new FileOutputStream(fileName, append);
} catch(FileNotFoundException ex) {
      String parentName = new File(fileName).getParent();
      if (parentName != null) {
         File parentDir = new File(parentName);
         if(!parentDir.exists() && parentDir.mkdirs()) {
            ostream = new FileOutputStream(fileName, append);
         } else {
            throw ex;
         }
      } else {
         throw ex;
      }
}
Writer fw = createWriter(ostream);//利用父类中的字节流->字符流转换方法
if(bufferedIO) {
  fw = new BufferedWriter(fw, bufferSize);
}
this.setQWForFiles(fw);//实例化父类中的QuitWriter（实际在上面指向了文件输出流）
this.fileName = fileName;
this.fileAppend = append;
this.bufferedIO = bufferedIO;
this.bufferSize = bufferSize;
writeHeader();
LogLog.debug("setFile ended");
  }

protected void setQWForFiles(Writer writer) {
 this.qw = new QuietWriter(writer, errorHandler);
}

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