字节流读取文件防止乱码

public static StringBuilder reader(String filePath) {
        try {
            File file = new File(filePath);
            if (file.isFile() && file.exists()) {
            	FileInputStream fileInputStream=new FileInputStream(file);
                byte[] b = new byte[fileInputStream.available()];
                StringBuilder sb = new StringBuilder();
                int len = -1;
                while( -1 != (len =fileInputStream.read(b)))
                {
                    byte[] temp = null;
                    temp = Arrays.copyOf(b, len); // 针对最后一次数据读入，防止从流中读入的数据中包含空格。
                    sb.append(new String(temp,"GBK"));
                }
                return sb;
            }
        } catch (UnsupportedEncodingException | FileNotFoundException e) {
            System.out.println("Cannot find the file specified!");
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("Error reading file content!");
            e.printStackTrace();
        }
        return null;
    }

byte[] b = new byte[fileInputStream.available()];
sb.append(new String(temp,“GBK”));
防止乱码