[英]How InputStream's read() method is implemented?
For the specific task I am trying to override read()
method for my custom class that extends InputStream. 对于特定的任务,我试图为扩展InputStream的自定义类重写read()
方法。
So far my implementation is: 到目前为止,我的实现是:
private ArrayList<byte[]> inputBuffer = new ArrayList<>();
...
@Override
public int read(@NonNull byte[] b) throws IOException {
if (inputBuffer.size() > 0) {
b = inputBuffer.get(0);
inputBuffer.remove(0);
} else
return -1;
return b.length;
}
And I am adding data to my InputStream
like this: 我正在像这样向我的InputStream
添加数据:
boolean writeDataToInputStream(byte[] data) {
int arrSize = inputBuffer.size();
if (data.length > 0) {
inputBuffer.add(data);
}
return arrSize < inputBuffer.size();
}
I've read documentation, I know how this method works by default. 我已经阅读了文档,我知道默认情况下该方法的工作方式。 But I need somehow to pass ArrayList
element to input parameter byte[] b
. 但是我需要以某种方式将ArrayList
元素传递给输入参数byte[] b
。
I've been coding in java for few years and yet I've never put attention to how this method is actually implemented. 我从事Java编程已经有好几年了,但是我从未关注过这种方法的实际实现方式。 How can I pass data to an incoming parameter and return the number of bytes from my ArrayList's element written? 如何将数据传递到传入参数,并从写入的ArrayList元素中返回字节数?
I have to use custom Socket specifically for BLE w/ Input and Output stream due to my architecture, where I use WiFi socket, BT socket. 由于我的体系结构,我必须使用专门用于BLE w /输入和输出流的自定义套接字,其中使用WiFi套接字,BT套接字。
Please uncover this mystery for me. 请为我揭开这个谜。
When you create your own InputStream
, the only method that you have to implement since it is an abstract
method is read()
which is also much less error prone than implementing read(byte[] b)
and/or read(byte b[], int off, int len)
. 创建自己的InputStream
,由于它是一个abstract
方法,因此您唯一需要实现的方法是read()
,它比实现read(byte[] b)
和/或read(byte b[], int off, int len)
错误发生率要小得多。 read(byte b[], int off, int len)
。 Moreover please note that the default implementation of read(byte b[], int off, int len)
already checks the arguments for you so unless you want to revalidate the arguments yourself, you should implement read()
only. 此外,请注意read(byte b[], int off, int len)
的默认实现已经为您检查了参数,因此,除非您想自己重新验证参数,否则应仅实现read()
。
So in your case this method could be: 因此,在您的情况下,此方法可能是:
// Current index in the last byte array read
private int index;
private List<byte[]> inputBuffer = new ArrayList<>();
...
@Override
public int read() throws IOException {
if (inputBuffer.isEmpty()) {
return -1;
}
// Get first element of the List
byte[] bytes = inputBuffer.get(0);
// Get the byte corresponding to the index and post increment the current index
byte result = bytes[index++];
if (index >= bytes.length) {
// It was the last index of the byte array so we remove it from the list
// and reset the current index
inputBuffer.remove(0);
index = 0;
}
return result;
}
However if you really want to implement read(byte b[], int off, int len)
, here is how it could look like: 但是,如果您确实要实现read(byte b[], int off, int len)
,则如下所示:
@Override
public int read(byte b[], int off, int len) throws IOException {
// Check parameters
if (b == null) {
throw new NullPointerException();
} else if (off < 0 || len < 0 || len > b.length - off) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
if (inputBuffer.isEmpty()) {
return -1;
}
int read = 0;
// Iterate as long as don't get the expected bytes amount and the list is not empty
do {
byte[] bytes = inputBuffer.get(0);
int lg = Math.min(bytes.length - index, len);
// Copy the bytes from "bytes" to "b"
System.arraycopy(bytes, index, b, off, lg);
// Update all counters
read += lg;
off += lg;
index += lg;
len -= lg;
if (index >= bytes.length) {
// It was the last index of the byte array so we remove it from the list
// and reset the current index
inputBuffer.remove(0);
index = 0;
}
} while (read < len && !inputBuffer.isEmpty());
return read;
}
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