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Document contentLength() behavior for InputStreamResource and custom subclasses 

Closes gh-33089
This commit is contained in:
Juergen Hoeller 2024-06-24 12:10:35 +02:00
parent 5f765fc8ce
commit 4e2fb308f6
2 changed files with 12 additions and 3 deletions
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4
framework-docs/modules/ROOT/pages/web/webmvc/mvc-controller/ann-methods/responseentity.adoc
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@ -40,7 +40,9 @@ content of the provided resource to the response `OutputStream`. Note that the
`InputStream` should be lazily retrieved by the `Resource` handle in order to reliably
close it after it has been copied to the response. If you are using `InputStreamResource`
for such a purpose, make sure to construct it with an on-demand `InputStreamSource`
(e.g. through a lambda expression that retrieves the actual `InputStream`).
(e.g. through a lambda expression that retrieves the actual `InputStream`). Also, custom
subclasses of `InputStreamResource` are only supported in combination with a custom
`contentLength()` implementation which avoids consuming the stream for that purpose.
Spring MVC supports using a single value xref:web/webmvc/mvc-ann-async.adoc#mvc-ann-async-reactive-types[reactive type]
to produce the `ResponseEntity` asynchronously, and/or single and multi-value reactive

11
spring-core/src/main/java/org/springframework/core/io/InputStreamResource.java
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@ -40,6 +40,13 @@ import org.springframework.util.Assert;
* times. This also applies when constructed with an {@code InputStreamSource}
* which lazily obtains the stream but only allows for single access as well.
*
* <p><b>NOTE: This class does not provide an independent {@link #contentLength()}
* implementation: Any such call will consume the given {@code InputStream}!</b>
* Consider overriding {@code #contentLength()} with a custom implementation if
* possible. For any other purpose, it is not recommended to extend from this
* class; this is particularly true when used with Spring's web resource rendering
* which specifically skips {@code #contentLength()} for this exact class only.
*
* @author Juergen Hoeller
* @author Sam Brannen
* @since 28.12.2003
@ -132,8 +139,8 @@ public class InputStreamResource extends AbstractResource {
@Override
public InputStream getInputStream() throws IOException, IllegalStateException {
if (this.read) {
throw new IllegalStateException("InputStream has already been read - " +
"do not use InputStreamResource if a stream needs to be read multiple times");
throw new IllegalStateException("InputStream has already been read (possibly for early content length " +
"determination) - do not use InputStreamResource if a stream needs to be read multiple times");
}
this.read = true;
return this.inputStreamSource.getInputStream();