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Support ETag generation on ResourceHttpRequestHandler

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Prior to this commit, the `ResourceHttpRequestHandler` would support
HTTP caching when serving resources, but only driving it through the
`Resource#lastModified()` information.

This commit introduces an ETag generator function that can be configured
on the `ResourceHttpRequestHandler` to dynamically generate an ETag
value for the Resource that is going to be served.

Closes gh-29031
This commit is contained in:
Brian Clozel
2023-10-25 11:44:31 +02:00
parent ebfa009f18
commit 7582bd8667
2 changed files with 63 additions and 2 deletions
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31
spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java
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@@ -25,6 +25,7 @@ import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.function.Function;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServletRequest;
@@ -141,6 +142,9 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
private boolean useLastModified = true;
@Nullable
private Function<Resource, String> etagGenerator;
private boolean optimizeLocations = false;
@Nullable
@@ -383,6 +387,29 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
return this.useLastModified;
}
/**
* Configure a generator function that will be used to create the ETag information,
* given a {@link Resource} that is about to be written to the response.
* <p>This function should return a String that will be used as an argument in
* {@link ServletWebRequest#checkNotModified(String)}, or {@code null} if no value
* can be generated for the given resource.
* @param etagGenerator the HTTP ETag generator function to use.
* @since 6.1
*/
public void setEtagGenerator(@Nullable Function<Resource, String> etagGenerator) {
this.etagGenerator = etagGenerator;
}
/**
* Return the HTTP ETag generator function to be used when serving resources.
* @return the HTTP ETag generator function
* @since 6.1
*/
@Nullable
public Function<Resource, String> getEtagGenerator() {
return this.etagGenerator;
}
/**
* Set whether to optimize the specified locations through an existence
* check on startup, filtering non-existing directories upfront so that
@@ -567,7 +594,9 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
checkRequest(request);
// Header phase
if (isUseLastModified() && new ServletWebRequest(request, response).checkNotModified(resource.lastModified())) {
String eTagValue = (this.getEtagGenerator() != null) ? this.getEtagGenerator().apply(resource) : null;
long lastModified = (this.isUseLastModified()) ? resource.lastModified() : -1;
if (new ServletWebRequest(request, response).checkNotModified(eTagValue, lastModified)) {
logger.trace("Resource not modified");
return;
}