-1 在读取文件 java 时检测到

Question

I am getting ambiguous outputs while reading from a server program in java :

byte [] mybytearray  = new byte [content_length]; 
InputStream inputStream = clientSocket0.getInputStream(); //Getting input 
from peer0
FileOutputStream fileOutputStream = new FileOutputStream(fileDownloaded); 
//Sending the output to local directory
BufferedOutputStream bufferedOutputStream = new 
BufferedOutputStream(fileOutputStream);

bytesRead = inputStream.read(mybytearray,0,content_length);
System.out.println("First read : " +bytesRead);
current = bytesRead;
if(bytesRead!=content_length) {
              current = bytesRead;
               do {
                        System.out.println(current +"-Current");
                        System.out.println("Read it : "+(mybytearray.length-current));
                        bytesRead =
                              inputStream.read(mybytearray, current, (mybytearray.length-current));
                          System.out.println("***"+bytesRead);
                         if(bytesRead == -1) {
                             //current = content_length;
                             break;
                         }
                         else 
                           current += bytesRead;
                     } while(current < content_length );
                }

                bufferedOutputStream.write(mybytearray, 0 , current);

                bufferedOutputStream.flush();
                bufferedOutputStream.close();
                inputStream.close();
                inFromServer0.close();

It is giving the following output for some files :

Content length 33996
C:\\Users\\Sumit\\git\\IP_Task2\\Task1\\Peer1/rfc8183.txt.pdf
First read : 24356
24356-Current
Read it : 9640
***-1

The bytesRead in loop are -1 thereby it is not able to create the correct file.

Answer 1

Whenever you use a method, you should read its documentation to see what values it can return.

Take a look at the description of InputStream.read(byte[], int, int) :

public int read(byte[] b, int off, int len) throws IOException

Reads up to len bytes of data from the input stream into an array of bytes. An attempt is made to read as many as len bytes, but a smaller number may be read. The number of bytes actually read is returned as an integer.

This method blocks until input data is available, end of file is detected, or an exception is thrown.

If len is zero, then no bytes are read and 0 is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

The first byte read is stored into element b[off], the next one into b[off+1], and so on. The number of bytes read is, at most, equal to len. Let k be the number of bytes actually read; these bytes will be stored in elements b[off] through b[off+k-1], leaving elements b[off+k] through b[off+len-1] unaffected.

In every case, elements b[0] through b[off] and elements b[off+len] through b[b.length-1] are unaffected.

The read(b, off, len) method for class InputStream simply calls the method read() repeatedly. If the first such call results in an IOException, that exception is returned from the call to the read(b, off, len) method. If any subsequent call to read() results in a IOException, the exception is caught and treated as if it were end of file; the bytes read up to that point are stored into b and the number of bytes read before the exception occurred is returned. The default implementation of this method blocks until the requested amount of input data len has been read, end of file is detected, or an exception is thrown. Subclasses are encouraged to provide a more efficient implementation of this method.

Parameters:

 b - the buffer into which the data is read. off - the start offset in array b at which the data is written. len - the maximum number of bytes to read.

Returns:

 the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Read that last line very carefully. -1 is a special return value that means no data was read because there is no additional input available in the InputStream .