JarFileArchive creates a JarFile that is never closed

[wilkinsona]

When a JarFileArchive is created with a File, it creates a JarFile instance that is never closed. There's no accessor for the underlying JarFile and no close() method so, without resorting to reflection, there's nothing that a user of JarFileArchive can do to avoid leaking an open file.

This problem affects our tests where the open files prevent JUnit 5 from cleaning up a temporary directory. We could resort to reflection in our tests to close the underlying JarFile, but we may want to fix it more "properly" which I think will require changes to public API.

[wilkinsona]

A "proper" fix would be to make Archive extend AutoCloseable, override close() to be a default method, and then implement it on JarFileArchive where it would delegate to JarFile.close():

diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/Archive.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/Archive.java
index 9d032f473f..ee6a9e86f5 100644
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/Archive.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/Archive.java
@@ -30,7 +30,7 @@ import org.springframework.boot.loader.Launcher;
  * @author Phillip Webb
  * @see JarFileArchive
  */
-public interface Archive extends Iterable<Archive.Entry> {
+public interface Archive extends Iterable<Archive.Entry>, AutoCloseable {
 
        /**
         * Returns a URL that can be used to load the archive.
@@ -54,6 +54,15 @@ public interface Archive extends Iterable<Archive.Entry> {
         */
        List<Archive> getNestedArchives(EntryFilter filter) throws IOException;
 
+       /**
+        * Closes the {@code Archive}, releasing any open resources.
+        * @throws Exception if an error occurs during close processing
+        */
+       @Override
+       default void close() throws Exception {
+
+       }
+
        /**
         * Represents a single entry in the archive.
         */
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/JarFileArchive.java b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/JarFileArchive.java
index 31dd40b00c..34b8ab0772 100755
--- a/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/JarFileArchive.java
+++ b/spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/archive/JarFileArchive.java
@@ -94,6 +94,11 @@ public class JarFileArchive implements Archive {
                return new EntryIterator(this.jarFile.entries());
        }
 
+       @Override
+       public void close() throws IOException {
+               this.jarFile.close();
+       }
+
        protected Archive getNestedArchive(Entry entry) throws IOException {
                JarEntry jarEntry = ((JarFileEntry) entry).getJarEntry();
                if (jarEntry.getComment().startsWith(UNPACK_MARKER)) {

The tests, and any other users of Archive, can then close Archive instances as needed.