Merge pull request #18477 from dsyer

* pr/18477:
  Polish "Add some more notes on running exploded jar files"
  Add some more notes on running exploded jar files

Closes gh-18477

spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-executable-jar-format.adoc

@@ -164,17 +164,44 @@ The classpath is deduced from the nested jars.
 
 
 [[executable-jar-exploded-archives]]
-=== Exploded Archives
-Certain PaaS implementations may choose to unpack archives before they run.
+=== Containers and Exploded Archives
+If you are running your application from a container, you can use the unexploded jar file as above, but it is also often an advantage to explode it and run it in a different way.
+Certain PaaS implementations may also choose to unpack archives before they run.
 For example, Cloud Foundry operates this way.
-You can run an unpacked archive by starting the appropriate launcher, as follows:
+The simplest way to run an unpacked archive is by starting the appropriate launcher, as follows:
 
 [indent=0]
 ----
-	$ unzip -q myapp.jar
+	$ jar -xf myapp.jar
 	$ java org.springframework.boot.loader.JarLauncher
 ----
 
+This is actually slightly faster on startup (depending on the size of the jar) than running from an unexploded archive.
+At runtime you shouldn't expect any differences.
+
+Once you have unpacked the jar file, you can also get an extra boost to startup time by running the app with its "natural" main method instead of the `JarLauncher`. For example:
+
+[indent=0]
+----
+	$ jar -xf myapp.jar
+	$ java -cp BOOT-INF/classes:BOOT-INF/lib/* com.example.MyApplication
+----
+
+More efficient container images can also be created by copying the dependencies to the image as a separate layer from the application classes and resources (which normally change more frequently).
+There is more than one way to achieve this layer separation.
+For example, using a `Dockerfile` you could express it in this form (assuming the jar is already unpacked at `target/dependency`):
+
+[indent=0]
+----
+FROM openjdk:8-jdk-alpine
+VOLUME /tmp
+ARG DEPENDENCY=target/dependency
+COPY ${DEPENDENCY}/BOOT-INF/lib /app/lib
+COPY ${DEPENDENCY}/META-INF /app/META-INF
+COPY ${DEPENDENCY}/BOOT-INF/classes /app
+ENTRYPOINT ["java","-cp","app:app/lib/*","com.example.MyApplication"]
+----
+
 
 
 [[executable-jar-property-launcher-features]]