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Merge pull request #18477 from dsyer

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

Closes gh-18477
This commit is contained in:
Stephane Nicoll
2019-10-15 10:03:08 +02:00
parent 391eb279df 4efb4d1dd3
commit 3dac8e9abd
1 changed files with 31 additions and 4 deletions
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35
spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-executable-jar-format.adoc
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@@ -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]]