java的InputStream獲取字節(jié)大小相關(guān)方法

1 通過StreamUtils工具類的copyToByteArray()方法獲?。ㄍ扑]）

正常大部分項(xiàng)目都是使用的Spring，而Spring已經(jīng)幫我們開發(fā)好了相應(yīng)的工具類，我們直接調(diào)用即可。

InputStream is = this.getClass().getResourceAsStream(filePath);
byte[] bytes = StreamUtils.copyToByteArray(is);
is.read(bytes);

2 通過available()方法獲?。ú煌扑]）

InputStream is = this.getClass().getResourceAsStream(filePath);
byte[] bytes = new byte[is.available()];
is.read(bytes);

2.1 不推薦理由

可以看一下方法注釋：

/**
 * Returns an estimate of the number of bytes that can be read (or
 * skipped over) from this input stream without blocking by the next
 * invocation of a method for this input stream. The next invocation
 * might be the same thread or another thread.  A single read or skip of this
 * many bytes will not block, but may read or skip fewer bytes.
 *
 * <p> Note that while some implementations of {@code InputStream} will return
 * the total number of bytes in the stream, many will not.  It is
 * never correct to use the return value of this method to allocate
 * a buffer intended to hold all data in this stream.
 *
 * <p> A subclass' implementation of this method may choose to throw an
 * {@link java.io.IOException} if this input stream has been closed by
 * invoking the {@link #close()} method.
 *
 * <p> The {@code available} method for class {@code InputStream} always
 * returns {@code 0}.
 *
 * <p> This method should be overridden by subclasses.
 *
 * @return ? ? an estimate of the number of bytes that can be read (or skipped
 * ? ? ? ? ? ? over) from this input stream without blocking or {@code 0} when
 * ? ? ? ? ? ? it reaches the end of the input stream.
 * @exception java.io.IOException if an I/O error occurs.
 */

大致意思是返回的字節(jié)數(shù)可能由于網(wǎng)絡(luò)原因阻塞一次只能返回部分字節(jié)或者另外一個(gè)線程也讀了導(dǎo)致返回部分字節(jié)，也就是說如果使用available()方法去獲取InputStream的長(zhǎng)度來作為字節(jié)數(shù)組的長(zhǎng)度，那可能會(huì)出現(xiàn)字節(jié)接受不完整的錯(cuò)誤，所以不推薦使用該方法的返回值去分配一個(gè)緩沖的byte數(shù)組。文章來源地址http://www.zghlxwxcb.cn/news/detail-726585.html

3 通過file.length()來獲取

File file = new File(path);
InputStream stream = new FileInputStream(file);
byte[] bytes = new byte[file.length()]

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