问题
It seems like it the Spring RestTemplate
isn't able to stream a response directly to file without buffering it all in memory. What is the proper to achieve this using the newer Spring 5 WebClient
?
WebClient client = WebClient.create("https://example.com");
client.get().uri(".../{name}", name).accept(MediaType.APPLICATION_OCTET_STREAM)
....?
I see people have found a few workarounds/hacks to this issue with RestTemplate
, but I am more interested in doing it the proper way with the WebClient
.
There are many examples of using RestTemplate
to download binary data but almost all of them load the byte[]
into memory.
回答1:
With recent stable Spring WebFlux (5.2.4.RELEASE as of writing):
final WebClient client = WebClient.create("https://example.com");
final Flux<DataBuffer> dataBufferFlux = client.get()
.accept(MediaType.TEXT_HTML)
.retrieve()
.bodyToFlux(DataBuffer.class); // the magic happens here
final Path path = FileSystems.getDefault().getPath("target/example.html");
DataBufferUtils
.write(dataBufferFlux, path, CREATE_NEW)
.block(); // only block here if the rest of your code is synchronous
For me the non-obvious part was the bodyToFlux(DataBuffer.class)
, as it is currently mentioned within a generic section about streaming of Spring's documentation, there is no direct reference to it in the WebClient section.
回答2:
Store the body to a temporary file and consume
static <R> Mono<R> writeBodyToTempFileAndApply(
final WebClient.ResponseSpec spec,
final Function<? super Path, ? extends R> function) {
return using(
() -> createTempFile(null, null),
t -> write(spec.bodyToFlux(DataBuffer.class), t)
.thenReturn(function.apply(t)),
t -> {
try {
deleteIfExists(t);
} catch (final IOException ioe) {
throw new RuntimeException(ioe);
}
}
);
}
Pipe the body and consume
static <R> Mono<R> pipeBodyAndApply(
final WebClient.ResponseSpec spec, final ExecutorService executor,
final Function<? super ReadableByteChannel, ? extends R> function) {
return using(
Pipe::open,
p -> {
final Future<Disposable> future = executor.submit(
() -> write(spec.bodyToFlux(DataBuffer.class), p.sink())
.log()
.doFinally(s -> {
try {
p.sink().close();
log.debug("p.sink closed");
} catch (final IOException ioe) {
throw new RuntimeException(ioe);
}
})
.subscribe(DataBufferUtils.releaseConsumer())
);
return just(function.apply(p.source()))
.log()
.doFinally(s -> {
try {
final Disposable disposable = future.get();
assert disposable.isDisposed();
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
});
},
p -> {
try {
p.source().close();
log.debug("p.source closed");
} catch (final IOException ioe) {
throw new RuntimeException(ioe);
}
}
);
}
回答3:
I cannot test whether or not the following code effectively does not buffer the contents of webClient
payload in memory. Nevertheless, i think you should start from there:
public Mono<Void> testWebClientStreaming() throws IOException {
Flux<DataBuffer> stream =
webClient
.get().accept(MediaType.APPLICATION_OCTET_STREAM)
.retrieve()
.bodyToFlux(DataBuffer.class);
Path filePath = Paths.get("filename");
AsynchronousFileChannel asynchronousFileChannel = AsynchronousFileChannel.open(filePath, WRITE);
return DataBufferUtils.write(stream, asynchronousFileChannel)
.doOnNext(DataBufferUtils.releaseConsumer())
.doAfterTerminate(() -> {
try {
asynchronousFileChannel.close();
} catch (IOException ignored) { }
}).then();
}
回答4:
I'm not sure if you have access to RestTemplate
in your current usage of spring, but this one have worked for me.
RestTemplate restTemplate // = ...;
RequestCallback requestCallback = request -> request.getHeaders()
.setAccept(Arrays.asList(MediaType.APPLICATION_OCTET_STREAM, MediaType.ALL));
// Streams the response
ResponseExtractor<Void> responseExtractor = response -> {
// Here I write the response to a file but do what you like
Path path = Paths.get("http://some/path");
Files.copy(response.getBody(), path);
return null;
};
restTemplate.execute(URI.create("www.something.com"), HttpMethod.GET, requestCallback, responseExtractor);
来源:https://stackoverflow.com/questions/56210186/spring-webclient-how-to-stream-large-byte-to-file