public String readFromFile(File src) {
        try {
            BufferedReader bufferedReader = new BufferedReader(new FileReader(
                    src));
            StringBuilder stringBuilder = new StringBuilder();
            String content;
            while((content = bufferedReader.readLine() )!=null){
                stringBuilder.append(content);
            }
            return stringBuilder.toString();
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return null;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return null;
        }

    }

java 读取文件转换成字符串