private String readFile(String filename){
		if (!filename.endsWith(".java")){
			System.out.println("该文本文件名不是以.java结尾的");
			return null;
		}
		BufferedReader in = null;
		try {
			in = new BufferedReader(new FileReader(filename));
		} catch (FileNotFoundException e) {
			System.out.println("File not found");
			//e.printStackTrace();
		}
		String s;
		StringBuilder sb = new StringBuilder();
		if (in != null){
			try {
				while((s = in.readLine()) != null){
					sb.append(s+"\n");
				}
				in.close();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		return sb.toString();
	}