为什么80%的码农都做不了架构师？>>> 
序
本文主要研究一下rocketmq的FileAppender
WriterAppender
org/apache/rocketmq/logging/inner/LoggingBuilder.java
public static class WriterAppender extends Appender {
protected boolean immediateFlush = true;
protected String encoding;
protected QuietWriter qw;
public WriterAppender() {
}
public void setImmediateFlush(boolean value) {
immediateFlush = value;
}
public boolean getImmediateFlush() {
return immediateFlush;
}
public void activateOptions() {
}
public void append(LoggingEvent event) {
if (!checkEntryConditions()) {
return;
}
subAppend(event);
}
protected boolean checkEntryConditions() {
if (this.closed) {
SysLogger.warn("Not allowed to write to a closed appender.");
return false;
}
if (this.qw == null) {
handleError("No output stream or file set for the appender named [" +
name + "].");
return false;
}
if (this.layout == null) {
handleError("No layout set for the appender named [" + name + "].");
return false;
}
return true;
}
public synchronized void close() {
if (this.closed) {
return;
}
this.closed = true;
writeFooter();
reset();
}
protected void closeWriter() {
if (qw != null) {
try {
qw.close();
} catch (IOException e) {
handleError("Could not close " + qw, e, CODE_CLOSE_FAILURE);
}
}
}
protected OutputStreamWriter createWriter(OutputStream os) {
OutputStreamWriter retval = null;
String enc = getEncoding();
if (enc != null) {
try {
retval = new OutputStreamWriter(os, enc);
} catch (IOException e) {
SysLogger.warn("Error initializing output writer.");
SysLogger.warn("Unsupported encoding?");
}
}
if (retval == null) {
retval = new OutputStreamWriter(os);
}
return retval;
}
public String getEncoding() {
return encoding;
}
public void setEncoding(String value) {
encoding = value;
}
public synchronized void setWriter(Writer writer) {
reset();
this.qw = new QuietWriter(writer, this);
writeHeader();
}
protected void subAppend(LoggingEvent event) {
this.qw.write(this.layout.format(event));
if (layout.ignoresThrowable()) {
String[] s = event.getThrowableStr();
if (s != null) {
for (String s1 : s) {
this.qw.write(s1);
this.qw.write(LINE_SEP);
}
}
}
if (shouldFlush(event)) {
this.qw.flush();
}
}
protected void reset() {
closeWriter();
this.qw = null;
}
protected void writeFooter() {
if (layout != null) {
String f = layout.getFooter();
if (f != null && this.qw != null) {
this.qw.write(f);
this.qw.flush();
}
}
}
protected void writeHeader() {
if (layout != null) {
String h = layout.getHeader();
if (h != null && this.qw != null) {
this.qw.write(h);
}
}
}
protected boolean shouldFlush(final LoggingEvent event) {
return event != null && immediateFlush;
}
}
- 这个接口定义了writeHeader、writeFooter、append等方法
- append方法这里参数是LoggingEvent，内部委托给subAppend
- subAppend方法调用layout进行格式化event，然后如果需要flush，则会直接对qw进行flush
FileAppender
org/apache/rocketmq/logging/inner/LoggingBuilder.java
public static class FileAppender extends WriterAppender {
protected boolean fileAppend = true;
protected String fileName = null;
protected boolean bufferedIO = false;
protected int bufferSize = 8 * 1024;
public FileAppender() {
}
public FileAppender(Layout layout, String filename, boolean append)
throws IOException {
this.layout = layout;
this.setFile(filename, append, false, bufferSize);
}
public void setFile(String file) {
fileName = file.trim();
}
public boolean getAppend() {
return fileAppend;
}
public String getFile() {
return fileName;
}
public void activateOptions() {
if (fileName != null) {
try {
setFile(fileName, fileAppend, bufferedIO, bufferSize);
} catch (IOException e) {
handleError("setFile(" + fileName + "," + fileAppend + ") call failed.",
e, CODE_FILE_OPEN_FAILURE);
}
} else {
SysLogger.warn("File option not set for appender [" + name + "].");
SysLogger.warn("Are you using FileAppender instead of ConsoleAppender?");
}
}
protected void closeFile() {
if (this.qw != null) {
try {
this.qw.close();
} catch (IOException e) {
if (e instanceof InterruptedIOException) {
Thread.currentThread().interrupt();
}
SysLogger.error("Could not close " + qw, e);
}
}
}
public boolean getBufferedIO() {
return this.bufferedIO;
}
public int getBufferSize() {
return this.bufferSize;
}
public void setAppend(boolean flag) {
fileAppend = flag;
}
public void setBufferedIO(boolean bufferedIO) {
this.bufferedIO = bufferedIO;
if (bufferedIO) {
immediateFlush = false;
}
}
public void setBufferSize(int bufferSize) {
this.bufferSize = bufferSize;
}
public synchronized void setFile(String fileName, boolean append, boolean bufferedIO, int bufferSize)
throws IOException {
SysLogger.debug("setFile called: " + fileName + ", " + append);
if (bufferedIO) {
setImmediateFlush(false);
}
reset();
FileOutputStream ostream;
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);
if (bufferedIO) {
fw = new BufferedWriter(fw, bufferSize);
}
this.setQWForFiles(fw);
this.fileName = fileName;
this.fileAppend = append;
this.bufferedIO = bufferedIO;
this.bufferSize = bufferSize;
writeHeader();
SysLogger.debug("setFile ended");
}
protected void setQWForFiles(Writer writer) {
this.qw = new QuietWriter(writer, this);
}
protected void reset() {
closeFile();
this.fileName = null;
super.reset();
}
}
- 写文件，这里定义了bufferSize为8 * 1024，如果开启bufferedIO，则创建的是BufferedWriter
- setQWForFiles方法根据指定的writer创建了QuietWriter
- setFile方法设置了qw之后，就直接writeHeader
QuietWriter
org/apache/rocketmq/logging/inner/LoggingBuilder.java
private static class QuietWriter extends FilterWriter {
protected Appender appender;
public QuietWriter(Writer writer, Appender appender) {
super(writer);
this.appender = appender;
}
public void write(String string) {
if (string != null) {
try {
out.write(string);
} catch (Exception e) {
appender.handleError("Failed to write [" + string + "].", e,
Appender.CODE_WRITE_FAILURE);
}
}
}
public void flush() {
try {
out.flush();
} catch (Exception e) {
appender.handleError("Failed to flush writer,", e,
Appender.CODE_FLUSH_FAILURE);
}
}
}
- QuietWriter继承自jdk的FilterWriter，实现了write(String)方法，重写了flush方法
- FilterWriter实现了write(int c)，write(char cbuf[], int off, int len)，write(String str, int off, int len)方法，用于对字符串进行过滤
小结
rocketmq的FileAppender继承自WriterAppender，采取的是根据layout对LoggingEvent来格式化，然后写入QuietWriter，最后写入到文件。
doc
- LoggingBuilder