文件处于磁盘上或者流处于内存中 在输入流有已知的和预处理的数据时，如在硬盘上的文件或者在流处于内存中。这种情况下，不需要做边界校验，并且内存容量条件允许的话，可以简单的读取并一次写入。
InputStream initialStream = new FileInputStream(new File(“src/main/resources/sample.txt”));
byte[] buffer = new byte[initialStream.available()];
initialStream.read(buffer);
File targetFile = new File(“src/main/resources/targetFile.tmp”);
OutputStream outStream = new FileOutputStream(targetFile);
outStream.write(buffer);
基于Guava的实现
InputStream initialStream = new FileInputStream(new File(“src/main/resources/sample.txt”));
byte[] buffer = new byte[initialStream.available()];
initialStream.read(buffer);
File targetFile = new File(“src/main/resources/targetFile.tmp”);
Files.write(buffer, targetFile);
基于Commons IO的实现
InputStream initialStream = FileUtils.openInputStream(new File(“src/main/resources/sample.txt”));
File targetFile = new File(“src/main/resources/targetFile.tmp”);
FileUtils.copyInputStreamToFile(initialStream, targetFile);
输入流映射正在进行的数据流 如果输入流链接到正在进行的数据流上，如来自正在进行的链接的HTTP响应，此时可能无法一次读取整个流。这种情况下，我们需要确保一直读取到流的尽头。
File targetFile = new File(“src/main/resources/targetFile.tmp”);
try(InputStream initialStream = new FileInputStream(new File(“src/main/resources/sample.txt”));
OutputStream outStream = new FileOutputStream(targetFile)) {
byte[] buffer = new byte[8 * 1024];
int bytesRead;
while ((bytesRead = initialStream.read(buffer)) != -1) {
outStream.write(buffer, 0, bytesRead);
}
} catch (Exception e) {
e.printStackTrace();
}
另一种实现方式：
try (InputStream initialStream = new FileInputStream(new File(“src/main/resources/sample.txt”))) {
File targetFile = new File(“src/main/resources/targetFile.tmp”);
java.nio.file.Files.copy(
initialStream,
targetFile.toPath(),
StandardCopyOption.REPLACE_EXISTING);
} catch (Exception e) {
e.printStackTrace();
}
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