java - java中用字节写入文件的概念是什么？

Question

我知道当我想写一个文件时，我应该使用这样的代码:

InputStream inputStream = new BufferedInputStream(url.openStream());
OutputStream outputStream = new FileOutputStream("/sdcard/myfile.jpg");

byte Data[] = new byte[1024];
long total = 0;

while ((count=inputStream.read(Data)) != -1) {
    total = total+count;
    outputStream.write(Data,0,count);
}

但是我不明白这个结果会发生什么，它是在写一个从零到100的图像文件吗？

谁能给我描述一下这是怎么发生的？谢谢

Answer 1

这段代码的作用是将 1024 字节读入临时缓冲区，将它们写入输出，然后重复，用输入中的下一个数据覆盖缓冲区的内容，直到没有更多数据为止。

代码功能的一些分割:

//get an InputStream from a URL, so we can download the data from it.
InputStream inputStream = new BufferedInputStream(url.openStream());

//Create an OutputStream so we can write the data we get from URL to the file
OutputStream outputStream = new FileOutputStream("/sdcard/myfile.jpg");

//create a temporary buffer to store the bytes we get from the URL
byte Data[] = new byte[1024];

long total = 0; //-< you don't actually use this anywhere..

//here, you read your InputStream (URL), into your temporary buffer, and you                                                
//also increment the count variable based on the number of bytes read.
//If there is no more data (read(...) returns -1) exit the loop, as we are finished.
while ((count=inputStream.read(Data)) != -1) {

    total = total+count;  //this is not actually used.. Also, where did you define "count" ?

    //write the content of the byte array "buffer" to the outputStream.
    //the "count" variable tells the outputStream how much you want to write.
    outputStream.write(Data,0,count);

   //After, do the whole thing again.
}

有趣的是循环控制语句:

while ((count=inputStream.read(Data)) != -1)

这里发生的是循环控制语句内的赋值。这与此等效，只是更短:

count = inputStream.read(Data);
while(count != -1) {

 ...do something

 count = inputStream.read(Data);
}

这里的另一件事是 inputStream.read(Data) 。这会将字节读取到临时缓冲区 ( Data )，并且它还返回读取的字节数，或 -1如果没有了。这使我们能够以简单的方式传输数据，就像这里一样，通过检查 read(...) 的返回值。控制数据的写入方式并在没有剩余数据时停止。

<小时/>

请注意，您应该始终关闭您的InputStream和OutputStream当不再需要它时，否则您可能会得到损坏或不完整的文件。您可以使用 .close() 来执行此操作方法。