从 AssetManager 读取文件作为 InputStream 后的 java.lang.NullPointerException

Question

AssetManager 定义及使用：

...
AssetManager mngr = getAssets();
try{
      encrypter.decrypt(mngr.open("sample.txt"),output_file);
}...(continued)

解密函数：

public void decrypt(InputStream in, OutputStream out)
    {
            try
            {
                    // Bytes read from in will be decrypted
                    in = new CipherInputStream(in, dcipher);
                    // Read in the decrypted bytes and write the cleartext to out
                    int numRead = 0;
                    while ((numRead = in.read(buf)) >= 0)
                    {
                      out.write(buf, 0, numRead);
                    }
                    out.close();
            ...(continued)

out.write(buf, 0, numRead); 行的错误是 java.lang.NullPointerException。

当用作以下调用时，此调用运行良好：

*encrypter.decrypt(new FileInputStream("sample.txt"),output_file)*（即从本地而不是android的资产目录读取文件时）；

有什么原因吗？

任何帮助表示赞赏！谢谢！

Answer 1

你的 OutputStream 没有初始化。所以你得到空指针异常。你可能想要 像这样的

 public void decrypt(InputStream in,String file)
        {
                try
                {
                 OutputStream out = new FileOutputStream(file);
                        // Bytes read from in will be decrypted
                        in = new CipherInputStream(in, dcipher);
                        // Read in the decrypted bytes and write the cleartext to out
                        int numRead = 0;
                        while ((numRead = in.read(buf)) >= 0)
                        {
                          out.write(buf, 0, numRead);
                        }
                        out.close();