JAVA實現讀取最后幾行日志

1. 背景

在項目框架設計中,針對系統產生的日志,有線上查看日志的需求.日志文件本身很大.線上查看時,開發人員只想了解當前系統產生的錯誤信息.

2. POM依賴

主要使用 ReversedLinesFileReader 實現到讀日志文件,需要引入commons-io依賴,底層使用 RandomAccessFile 實現.

 <dependency>
  <groupId>commons-io</groupId>
  <artifactId>commons-io</artifactId>
  <version>2.6</version>
 </dependency>

3. 代碼實現

先倒序讀取每行數據,放入集合中.然后集合倒序,返回符合閱讀習慣的文本日志.

public String readLastLines(String filePath, int lines) throws IOException {
  if(StringUtils.isBlank(filePath)|| lines<=0){
    return "";
  }
  List<String> lastLine = new ArrayList<String>();
  ReversedLinesFileReader reader = null;
  try {
    reader = new ReversedLinesFileReader(filePath, StandardCharsets.UTF_8);
    String line = "";
    while ((line = reader.readLine()) != null && lastLine.size() < lines) {
      lastLine.add(line);
    }
    Collections.reverse(lastLine);
  } catch (IOException e) {
    System.out.println("讀取文件失敗,公眾號:小滿小慢,小游戲:地心俠士");
  } finally {
    if (reader != null) {
      try {
        reader.close();
      } catch (IOException e) {
        System.out.println("關閉文件失敗,,公眾號:小滿小慢,小游戲:地心俠士");
      }
    }
  }
  return StringUtils.join(lastLine, "\r\n");
}

4. RandomAccessFile 基本使用

使用 RandomAccessFile類，實現倒序讀取內容

@Test
   public void testReadLogFile() {
   	File logFile = new File("./logs/spring.log");
   	RandomAccessFile reader = null;
   	try {
   		reader = new RandomAccessFile(logFile, "r");
   		System.out.println(reader.readUTF());
   		reader.seek(logFile.length() - 1);
   		byte c = -1;
   		List<Byte> l = new ArrayList<Byte>();
   		do {
   			c = reader.readByte();
   			if (c == '\r' || c == '\n') {
   				byte[] bytes = new byte[l.size()];
   				for (int i = 0; i < l.size(); i++) {
   					bytes[i] = l.get(i);
   				}
   				String line = new String(bytes, StandardCharsets.UTF_8);
   				System.out.println("地心俠士:"+ line);
   				l = new ArrayList<Byte>();
   			}
   		} while (reader.getFilePointer() != logFile.length());
   		System.out.println("地心俠士:" +logFile.length());
   	} catch (IOException e) {
   		e.printStackTrace();
   	} finally {
   		if (reader != null) {
   			try {
   				reader.close();
   			} catch (IOException e) {

   			}
   		}
   	}
   }