For this post I did some experiments with Java 15, reusing the Ubuntu 64bit SD card which was also used for the earlier post “Comparing a REST H2 Spring versus Quarkus application on Raspberry Pi” .

That version of Ubuntu comes with OpenJDK 11 pre-installed.

$ java -version
openjdk version "11.0.8" 2020-07-14
OpenJDK Runtime Environment (build 11.0.8+10-post-Ubuntu-0ubuntu120.04)
OpenJDK 64-Bit Server VM (build 11.0.8+10-post-Ubuntu-0ubuntu120.04, mixed mode)

Installing Azul Zulu 15

The OpenJDK Java 15 version was released on 2020-09-15, check out the Java Version Almanac for more details. Immediately after, Azul also release a new version of their free Zulu Embedded JDK, including a version for ARM 64-bit , so ideal for the latest Raspberry Pi boards!

With the SDKMAN tool you can get a list of available JDKs and switch to Java 15 with a single command sdk install java 15.0.0-zulu.

$ sdk list java

================================================================================
Available Java Versions
================================================================================
 Vendor        | Use | Version      | Dist    | Status     | Identifier
--------------------------------------------------------------------------------
 AdoptOpenJDK  |     | 11.0.8.hs    | adpt    |            | 11.0.8.hs-adpt      
               |     | 8.0.252.hs   | adpt    |            | 8.0.252.hs-adpt     
 Amazon        |     | 11.0.8       | amzn    |            | 11.0.8-amzn         
               |     | 8.0.262      | amzn    |            | 8.0.262-amzn        
 Azul Zulu     |     | 15.0.0       | zulu    |            | 15.0.0-zulu         
 BellSoft      |     | 14.0.2.fx    | librca  |            | 14.0.2.fx-librca    
               |     | 14.0.2       | librca  |            | 14.0.2-librca       
               |     | 11.0.8.fx    | librca  |            | 11.0.8.fx-librca    
               |     | 11.0.8       | librca  |            | 11.0.8-librca       
               |     | 8.0.265      | librca  |            | 8.0.265-librca      
 Java.net      |     | 16.ea.15     | open    |            | 16.ea.15-open       
               |     | 15           | open    |            | 15-open             
================================================================================
Use the Identifier for installation:

    $ sdk install java 11.0.3.hs-adpt
================================================================================

$ sdk install java 15.0.0-zulu

$ java -version
openjdk version "15" 2020-09-15
OpenJDK Runtime Environment Zulu15.27+17-CA (build 15+36)
OpenJDK 64-Bit Server VM Zulu15.27+17-CA (build 15+36, mixed mode)

Comparing startup speeds

To compare the startup speed I reused the Spring and Quarkus applications of the previous articles. I started both of them three times with JDK 11 and 15.

“A Spring REST and H2 database application on the Raspberry Pi”

$ cd JavaOnRaspberryPi/Chapter_10_Spring/java-spring-rest-db/target/
$ java -jar java-spring-rest-db-0.0.1-SNAPSHOT.jar

“Comparing a REST H2 Spring versus Quarkus application on Raspberry Pi”

$ cd JavaQuarkusRestDb/target/
$ java -jar javaquarkusrestdb-1.0-SNAPSHOT-runner.jar

Startup results

No important differences here, the newer JDK doesn’t seem to have any influence here.

JDK	Run	Spring	Quarkus
OpenJDK 11	1	37s	10s
	2	37s	9s
	3	38s	10s
Azul Zulu 15	1	39s	10s
	2	36s	10s
	3	37s	10s

Thread and memory analysis with VisualVM

Let’s go a step deeper and use VisualVM to inspect the application. I installed this on my Ubuntu PC with sudo apt install visualvm and extended the startup commands on the Raspberry Pi so a connection can be made from another PC.

$ java -Dcom.sun.management.jmxremote \
    -Dcom.sun.management.jmxremote.port=9010 \
    -Dcom.sun.management.jmxremote.local.only=false \
    -Dcom.sun.management.jmxremote.authenticate=false \
    -Dcom.sun.management.jmxremote.ssl=false \
    -jar javaquarkusrestdb-1.0-SNAPSHOT-runner.jar

I waited each time 2 minutes before taking a screenshot.

Spring application on Raspberry Pi with Java 11

Quarkus application on Raspberry Pi with Java 11

Spring application on Raspberry Pi with Java 15

Quarkus application on Raspberry Pi with Java 15

Profiling conclusions

Framework	JDK	Running CPU	Heap Size	Loaded classes
Spring	OpenJDK 11	< 20%	132 MB	13316
Spring	Azul Zulu 15	< 10%	157 MB	13200
Quarkus	OpenJDK 11	< 10%	90 MB	7463
Quarkus	Azul Zulu 15	< 10%	50 MB	7368

Conclusions

Do you need to switch from Java 11 to 15? No, not really based on these results. But each new version has bug and security fixes, new features, and generic improvements.

Don’t forget to check the list of highlights for this release which includes a few big development improvements, including text blocks (JEP 378) which will allow you to write cleaner code.

Azul Zulu OpenJDK 15 on Raspberry Pi