Java 我们如何读取或使用 outputstream 的内容

How can we read or use the contents of outputstream

提问by Amit Kumar

How can we read or use the contents of outputstream. In my case, I am using a method having signature.

我们如何读取或使用 outputstream 的内容。就我而言，我使用的是具有签名的方法。

public static OutputStream decryptAsStream(InputStream inputStream, String encryptionKey)

公共静态输出流解密AsStream（输入流输入流，字符串加密密钥）

This method return OutputStream. I want get OutputStream to String. Is it possible to pipe the output from an java.io.OutputStream to a String in Java?

此方法返回OutputStream。我想将 OutputStream 转换为 String。是否可以将 java.io.OutputStream 的输出通过管道传输到 Java 中的字符串？

回答by NINCOMPOOP

If you got the OutputStreamfrom the response, you can write the contents of the OutputStreamto the response which will be sent back to the browser . Sample code :

如果您OutputStream从 获得response，您可以将 的内容写入OutputStream将被发送回浏览器的响应。示例代码：

OutputStream outStream = response.getOutputStream();
response..setHeader("Content-Disposition", "attachment; filename=datafile.xls");
response.setContentType("application/vnd.ms-excel");
byte[] buf = new byte[4096];
int len = -1;
while ((len = inStream.read(buf)) != -1) {
    outStream.write(buf, 0, len);
}

outStream.flush();
outStream.close();

Read this : Content-Disposition:What are the differences between “inline” and “attachment”?

阅读本文：Content-Disposition：“内联”和“附件”有什么区别？

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In your case the method definition is :

在您的情况下，方法定义是：

public static OutputStream decryptAsStream(InputStream inputStream,
                                            String encryptionKey)

So you can get the OutputStreamfrom that method as :

所以你可以OutputStream从那个方法中得到：

OutputStream os = ClassName.decryptAsStream(inputStream,encryptionKey);

And then use the os.

然后使用os.

回答by Ushani

You can do something like following :

您可以执行以下操作：

  OutputStream output = new OutputStream()
    {
        private StringBuilder string = new StringBuilder();
        @Override
        public void write(int x) throws IOException {
            this.string.append((char) x );
        }

        public String toString(){
            return this.string.toString();
        }
    };

回答by UVM

Mainly you can use outputstreamsto send the file contents as @The New Idiot mentioned. .pdf files, zip file, image files etc.

主要是您可以outputstreams像@The New Idiot 提到的那样发送文件内容。.pdf 文件、zip 文件、图像文件等。

In such scenarios, get the output stream of your servlet and to that write the contentes

在这种情况下，获取 servlet 的输出流并写入内容

OutputStream outStream = response.getOutputStream();
FileInputSteram fis = new FileInputStream(new File("abc.pdf));
byte[] buf = new byte[4096];
int len = -1;
while ((len = fis.read(buf)) != -1) {
    outStream .write(buf, 0, len);
}
response.setContentType("application/octect");(if type is binary) else 
response.setContentType("text/html");
outStream .flush();
outStream.close();

回答by Stephen C

How can we read or use the contents of outputstream.

我们如何读取或使用 outputstream 的内容。

In general you can't. An OutputStreamis an object that you write bytes to. The general API doesn't provide any way to get the bytes back.

一般来说你不能。AnOutputStream是您向其写入字节的对象。通用 API 不提供任何方式来取回字节。

There are specific kinds of output stream that would allow you to get the bytes back. For instance:

有特定类型的输出流可以让您取回字节。例如：

• A ByteArrayOutputStreamhas a method for getting the byte array contents.
• A PipeOutputStreamhas a corresponding PipeInputStreamthat you can read from.
• If you use a FileOutputStreamto write to file, you can typicallyopen a FileInputStreamto read the file contents ... provided you know the file pathname.

• AByteArrayOutputStream有一种获取字节数组内容的方法。
• APipeOutputStream有一个对应的PipeInputStream，您可以从中读取。
• 如果您使用 aFileOutputStream写入文件，您通常可以打开 aFileInputStream来读取文件内容……前提是您知道文件路径名。

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Looking at that method, it strikes me that the method signature is wrongfor what you are trying to do. If the purpose is to provide an encrypter for a stream, then the method should return an InputStream. If the purpose is to write the encrypted data somewhere, then the method should return voidand take an extra parameter that is the OutputStreamthat the method should write to. (And then the caller can use an OutputStreamsubclass to capture the encrypted data ... if that is what is desired.)

看着那个方法，我觉得方法签名对于你想要做的事情是错误的。如果目的是为流提供加密器，则该方法应返回一个InputStream. 如果目的是将加密数据写入某处，则该方法应返回void并采用OutputStream该方法应写入的额外参数。（然后调用者可以使用OutputStream子类来捕获加密数据......如果这是需要的话。）

Another alternative that would "work" is to change the method's signature to make the return type ByteArrayOutputStream(or a file name). But that is not a good solution because it takes away the caller's ability to decide where the encrypted output should be sent.

另一种“有效”的替代方法是更改​​方法的签名以生成返回类型ByteArrayOutputStream（或文件名）。但这不是一个好的解决方案，因为它剥夺了调用者决定加密输出应该发送到哪里的能力。

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UPDATE

更新

Regarding your solution

关于你的解决方案

    OutputStream os = AESHelper.decryptAsStream(sourceFile, encryptionKey);
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    baos = (ByteArrayOutputStream) os;  
    byte[] imageBytes = baos.toByteArray();  
    response.setContentType("image/jpeg");  
    response.setContentLength(imageBytes.length);  
    OutputStream outs = response.getOutputStream();  
    outs.write(imageBytes);

That could work, but it is poor code:

这可以工作，但代码很差：

• If AESHelper.decryptAsStreamis a method that you wrote (and it looks like it is!), then you should declare it as returning a ByteArrayOutputStream.

• If it is already declared as returning a ByteArrayOutputStreamyou should assign it directly to baos.

• Either way, you should NOT initialize baosto a newly created ByteArrayOutputStreaminstance that immediately gets thrown away.

• 如果AESHelper.decryptAsStream是您编写的方法（看起来确实如此！），那么您应该将其声明为返回一个ByteArrayOutputStream.

• 如果它已声明为返回 a ByteArrayOutputStream，则应将其直接分配给baos.

• 无论哪种方式，您都不应该初始化baos为ByteArrayOutputStream立即被丢弃的新创建的实例。

It is also worth noting that the Content-Type is incorrect. If you sent that response to a browser, it would attempt to interpret the encrypted data as an image ... and fail. In theory you could set a Content-Encoding header ... but there isn't one that is going to work. So the best solution is to send the Content-Type as "application/octet-stream".

还值得注意的是 Content-Type 不正确。如果您将该响应发送到浏览器，它会尝试将加密数据解释为图像……并失败。理论上你可以设置一个 Content-Encoding 标头......但没有一个可以工作。所以最好的解决方案是将 Content-Type 作为“application/octet-stream”发送。