Java 读取流的IO差异

Question

你能帮我弄清楚流吗？为什么在教程中我发现当从文件中读取时，我们使用 len != -1（例如）。而当从流中读取然后写入流时，我们使用 len> 0.What 是不同的什么时候读书？

PS 以下代码取自示例

byte[] buffer = new byte[1024];
int len;
while ((len = in.read(buffer)) != -1) {
    out.write(buffer, 0, len);
}

 byte[] buf = new byte[8192];
    int length;
    while ((length = source.read(buf)) > 0) {
        target.write(buf, 0, length);
    }
}

UPD

link1

link2

link3

UPD 2

你也可以看看IOUtils.copy和Files.copy他们也有区别

UPD 3

我看read方法不return0，或者可用字节数，或者-1。谢谢大家

Answer 1

没有区别。 InputStream.read(byte[]) 的 javadoc 表示如下：

If the length of [the buffer] 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 the end of the file, the value -1 is returned; otherwise, at least one byte is read and stored into b.

和

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.

仔细阅读以上内容会告诉我们，如果缓冲区大小为零，read 只会 return 为零。

您的两个示例中的缓冲区大小不为零。因此 len != -1 和 length > 0 将具有相同的效果。

Java 读取流的IO差异

Java IO difference in reading streams

java

io

inputstream

stream