Getting InputStream with RestTemplate

by

The previous answers are not wrong, but they don’t go into the depth that I like to see. There are cases when dealing with low level InputStream is not only desirable, but necessary, the most common example being streaming a large file from source (some web server) to destination (a database). If you try to use a ByteArrayInputStream, you will be, not so surprisingly, greeted with OutOfMemoryError. Yes, you can roll your own HTTP client code, but you’ll have to deal with erroneous response codes, response converters etc. If you are already using Spring, looking to RestTemplate is a natural choice.

As of this writing, spring-web:5.0.2.RELEASE has a ResourceHttpMessageConverter that has a boolean supportsReadStreaming, which if set, and the response type is InputStreamResource, returns InputStreamResource; otherwise it returns a ByteArrayResource. So clearly, you’re not the only one that asked for streaming support.

However, there is a problem: RestTemplate closes the response soon after the HttpMessageConverter runs. Thus, even if you asked for InputStreamResource, and got it, it’s no good, because the response stream has been closed. I think this is a design flaw that they overlooked; it should’ve been dependent on the response type. So unfortunately, for reading, you must consume the response fully; you can’t pass it around if using RestTemplate.

Writing is no problem though. If you want to stream an InputStream, ResourceHttpMessageConverter will do it for you. Under the hood, it uses org.springframework.util.StreamUtils to write 4096 bytes at a time from the InputStream to the OutputStream.

Some of the HttpMessageConverter support all media types, so depending on your requirement, you may have to remove the default ones from RestTemplate, and set the ones you need, being mindful of their relative ordering.

Last but not the least, implementations of ClientHttpRequestFactory has a boolean bufferRequestBody that you can, and should, set to false if you are uploading a large stream. Otherwise, you know, OutOfMemoryError. As of this writing, SimpleClientHttpRequestFactory (JDK client) and HttpComponentsClientHttpRequestFactory (Apache HTTP client) support this feature, but not OkHttp3ClientHttpRequestFactory. Again, design oversight.

Edit:
Filed ticket SPR-16885.

More Related Contents:

  1. How do I read / convert an InputStream into a String in Java?
  2. Convert InputStream to byte array in Java
  3. How can an app use files inside the JAR for read and write?
  4. How can I read a text file in Android?
  5. How do I convert a String to an InputStream in Java?
  6. Read input stream twice
  7. How to clone an InputStream?
  8. Multipart File Upload Using Spring Rest Template + Spring Web MVC
  9. Connecting an input stream to an outputstream
  10. Java InputStream blocking read
  11. How to identify end of InputStream in java
  12. Why does InputStream#read() return an int and not a byte?
  13. Generics with Spring RESTTemplate
  14. How to POST form data with Spring RestTemplate?
  15. How to read file from ZIP using InputStream?
  16. spring mvc rest service redirect / forward / proxy
  17. Reading streams from java Runtime.exec
  18. How to convert InputStream to virtual File
  19. Unable to read InputStream from Java Process (Runtime.getRuntime().exec() or ProcessBuilder)
  20. InputStream from a URL
  21. Determine the size of an InputStream
  22. Most efficient way to create InputStream from OutputStream
  23. Reading a binary input stream into a single byte array in Java
  24. How to use multiple Scanner objects on System.in in Java?
  25. How do I convert an OutputStream to an InputStream?
  26. How to Cache InputStream for Multiple Use
  27. Looping Error on Android Emulator
  28. ClassLoader getResourceAsStream returns null
  29. spring resttemplate url encoding
  30. RestTemplate with pem certificate

Leave a Comment