1、读取

	public String GetLogString(String logpath){	
		System.out.println("----------------开始读取日志----------------");
		File logfile = new File(logpath+"\\log.txt");
		String totalstr = "";
		if(logfile.exists()){
			try {
				FileReader fr = new FileReader(logfile);
				BufferedReader br = new BufferedReader(fr);
				String line = "";
				while ((line = br.readLine()) != null){  //按行读取文件流的内容
					totalstr = totalstr + line +",";	
				}
				fr.close();
				br.close();	
			} catch (Exception e) {
				e.printStackTrace();
			}				
		}else{
			System.out.println("日志文件不存在");
		}
		return totalstr;
	}

2、追加写入

/**
    * 写入TXT，追加写入
    * @param filePath
    * @param content
    */
    public static void fileChaseFW(String filePath, String content) {
        try {
            //构造函数中的第二个参数true表示以追加形式写文件
            FileWriter fw = new FileWriter(filePath,true);
            fw.write(content);
            fw.close();
        } catch (IOException e) {
            System.out.println("文件写入失败！" + e);
        }
    }
    public static void main(String[] args) throws Exception{
        File file = new File("D:\\123wu吴.txt");
        createFile(file);
        readTxtFile(file);
        fileChaseFW("D:\\123wu吴.txt","66666666");
    }
}

3、覆盖写入

/**

    * 写入TXT，覆盖原内容
    * @param content
    * @param fileName
    * @return
    * @throws Exception
    */

    public void writeTxtFile(String content,File fileName)throws Exception{
        FileWriter fw = new FileWriter(fileName);
            fw.write(content);
            fw.close();
    }