[英]How to resume download with Spring RestTemplate?
我正在使用RestTemplate从Nexus服务器下载文件(大约350 mb)。 此帖中提供的代码适用于此目的:
RestTemplate restTemplate // = ...;
// Optional Accept header
RequestCallback requestCallback = request -> request.getHeaders()
.setAccept(Arrays.asList(MediaType.APPLICATION_OCTET_STREAM, MediaType.ALL));
// Streams the response instead of loading it all in memory
ResponseExtractor<Void> responseExtractor = response -> {
// Here I write the response to a file but do what you like
Path path = Paths.get("some/path");
Files.copy(response.getBody(), path);
return null;
};
restTemplate.execute(URI.create("www.something.com"), HttpMethod.GET, requestCallback, responseExtractor);
我想检查文件是否存在,然后尝试恢复下载:
...
if(Files.exists(path)) {
log.info("{} exists. Attempting to resume download", path);
Files.write(path, StreamUtils.copyToByteArray(response.getBody()), StandardOpenOption.APPEND);
} else {
Files.copy(response.getBody(), path);
}
但这只会导致OOM错误:
java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Unknown Source) ~[na:1.8.0_191]
at java.io.ByteArrayOutputStream.grow(Unknown Source) ~[na:1.8.0_191]
at java.io.ByteArrayOutputStream.ensureCapacity(Unknown Source) ~[na:1.8.0_191]
at java.io.ByteArrayOutputStream.write(Unknown Source) ~[na:1.8.0_191]
...
我已经使用带有curl的Range标头测试了该调用,并确定Nexus支持该调用。 我这样设置:
long bytes = path.toFile().length();
...
request.getHeaders().setRange(Arrays.asList(HttpRange.createByteRange(bytes)));
我猜测上面的内存错误是因为InputStream阻塞。 所以我尝试使用Channel / Buffer代替:
...
try {
if(Files.exists(path)) {
log.info("{} exists. Attempting to resume download", path);
ReadableByteChannel channel = Channels.newChannel(response.getBody());
FileChannel fileChannel = FileChannel.open(path, StandardOpenOption.APPEND);
fileChannel.tryLock();
ByteBuffer buffer = ByteBuffer.allocate(4096);
int bytesRead = 0;
while((bytesRead = channel.read(buffer)) != -1) {
fileChannel.write(buffer);
buffer.clear();
}
fileChannel.close();
} else {
Files.copy(response.getBody(), path);
}
...
这至少会将一些数据写入文件但仍然失败。 我对java.nio设施没有太多经验,所以任何帮助都表示赞赏。
*编辑:感谢任何答案,但我被迫使用JDK 8进行此项目。
如果使用大文件以确保不在内存中读取流,则需要以下代码行:
SimpleClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();
requestFactory.setBufferRequestBody(false);
restTemplate.setRequestFactory(requestFactory);
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