Leaner microservices with Java 10

Leaner microservices with
Java 10, Spring Boot 2,
and Docker
arto.santala@solita.fi

Who am I?
• Arto Santala
• Work as software architect in Solita, producing tailored
solutions to accelerate customer business
• More than 20 years of experience making customers
dreams come true with application of proper technologies
and methodologies
• Guilty of writing a lot of horrible code in the 90’s that
should be burned with fire. Always aiming to improve.
• Passionate about agile and automation. Trying to make
every moment worthy of living.

Java 8 as platform
• Java 8 is product of more than 20 years of development. Every
release, more and more have been added, nothing has never
been removed
• Today Java 8 is a heavy platform with a lot of libraries that you
will never need
• Midi instruments, 1995 version of java.util.Date, Corba IIOP, applets,
AWT, …
• Heavier images, larger memory footprint, more attack area for
vulnerabilities

Java 8 + Spring Boot Helloworld

Java 9 as platform
• Modular JDK, Modular source code, Modular run-time images, Module system, Modular
application packaging, Java platform module system, etc
• Also: Jshell, new HTTP client (HttpRequest/HttpResponse), Process API, Pub/Sub
framework, immutable set/list, Optional to Stream, etc
module fi.solita.java9training.api {
requires fi.solita.java9training.services;
exports fi.solita.java9training.api;
}
Set<String> mySet = Set.of(”val1", ”val2", ”val3");
List<String> myList = List.of(”val1”,”val2”,”val3”);

Java 10 as platform
• Not such a revolution, just a bit of evolution
• Hard transition from Java 8 to Java 9
• Easy transition from Java 9 to 10 and 11
• GA is out there now – but do note the short support lifetime for both Java 9 and 10
var item1 = ”HELLO”;
var list1 = List.of(item1,”WORLD”);

Java 10 + Spring Boot Helloworld
Still fat, but getting better!
Pssst, minimal Java 10 + Apache Spark web services

JLINK
jlink --module-path $JAVA_HOME/jmods --verbose --add-modules
java.base,java.logging,java.xml,jdk.unsupported,java.sql,java.naming,java.desktop,java.man
agement,java.security.jgss,java.instrument --compress 2 --no-header-files --output jdk-9-
minimal-osx --no-man-pages
Jlink is a new tool that allows to link modules and even JRE together as a platform specific
executable.
For example, you can generate a custom JRE with just the modules you need to run Spring
Boot, like this:
Much less attack surface, less to update, less disk use, less memory use, faster startup, etc

Java Support Roadmap
http://www.oracle.com/technetwork/java/eol-135779.html

Maven source level
<properties>
<maven.compiler.source>10</maven.compiler.source>
<maven.compiler.target>10</maven.compiler.target>
</properties>

Maven compiler plugin
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.7.0</version>
<configuration>
<release>10</release>
</configuration>
<dependencies>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm</artifactId>

</dependency>
</dependencies>
</plugin>

Spring Boot 2
• Spring Boot 1.x is not going to support Java 9 or above, ever
• Spring Boot 2 is out there, with support to Java 9 (and to some extent also
10)
• Easiest to get started with Spring Initializr at https://start.spring.io/

Quick (stupid) test
@RestController
public class HelloController {
@RequestMapping(method = RequestMethod.GET)
public Map getGreeting() {
var now = Instant.now();
return Map.of("message", String.format("It's %s", now));
}
}

Typical pitfalls with Java 9/10
• package javax.xml.bind.annotation.adapters is not visible
• More and more core modules are missing from core of core, so you need to either add them via
command line switches, or declare module dependencies – or just as dependencies
• --add-modules java.xml.bind
• Illegal reflective access by org.springframework.cglib.core.ReflectUtils
• Java 9/10 is starting to be more precise on accessing non-public APIs, so primarily you should find
libraries that are not accessing internal APIs
• Ironically, with Spring you can make this warning go away by setting –illegal-access=deny
• In some cases. as short-term solution you can also play with --add-
exports $module/$package=$readingmodule and --add-opens $module/$package=$readingmodule to
open up types and members for deep reflection of also private internals
• So mostly, just make sure dependencies and modules are declared properly, and find libraries
that play nicely with Java 9/10/11 and do not leverage the deprecated internals
• In future, more and more modules and packages will go out of core, so get used to this

Typical pitfalls with Java 9/10
• IllegalArgumentException at testCompilation/test phase
• Maven compiler/surefire might be using older version of ASM, which can be fixed like this:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<release>10</release>
</configuration>
<dependencies>
<dependency>
<groupId>org.ow2.asm</groupId>
<artifactId>asm</artifactId>
<version>6.1.1</version> 
</dependency>
</dependencies>
</plugin>

Other non-default (EE) modules
• java.activation with javax.activation package
• java.corba with javax.activity, javax.rmi, javax.rmi.CORBA, andorg.omg.* packages
• java.transaction with javax.transaction package
• java.xml.bind with all javax.xml.bind.* packages
• java.xml.ws with javax.jws, javax.jws.soap, javax.xml.soap, and alljavax.xml.ws.* packages
• java.xml.ws.annotation with javax.annotation package
• Java 11 will remove all these, so it will not be enough to just --add-modules forever, you
need to find the actual libraries and declare as real, external dependencies

XML modules will go out from core
<dependency>
<groupId>javax.xml.bind</groupId>
<artifactId>jaxb-api</artifactId>
</dependency>
<dependency>
<groupId>com.sun.xml.bind</groupId>
<artifactId>jaxb-core</artifactId>
</dependency>
<dependency>
<groupId>com.sun.xml.bind</groupId>
<artifactId>jaxb-impl</artifactId>
</dependency>

Evaluating old code
• java --list-modules
• jdeps --jdk-internals -R --class-path 'libs/*' $project
• --illegal-access=$value option, where $value can be:
• permit: Access to all JDK-internal APIs is permitted to code on the class path. For reflective access,
a single warning is issued for the first access to each package. (Default is Java 9, but will be
removed in a future release.)
• warn: Behaves like permit but a warning is issued for each reflective access.
• debug: Behaves like warn but a stack trace is included in each warning.
• deny: The option for those who believe in strong encapsulation:
• All illegal access is forbidden by default.
• jar –file=mylib.jar --describe-modules
• To figure out automatic module name for the .jar

Typical pitfalls with Spring Boot 2
• Security module has changed a lot: Now you only get what you declare, unlike previously
when there were a lot of defaults
• Spring Data APIs have changed a lot: Now there’s a lot more of Optional use for return
values, and more descriptive names for methods
• Later version of Flyway, not checksum compatible with old version possibly
• References to old versions of Spring modules, or third party modules that depend on 1.x
versions

Docker
• Docker is a lovely way to start experimenting with Java 9/10 without installing it on your
own machine
• docker run -it solita/jdk10
• You can map folders to Docker so you can access files in them, such as .jar files, libraries,
etc – you can also expose ports where services run to host machines
• docker run -it -p 8080:8080 -v `pwd`:/root solita/jdk10
• This is just an example, you can take a look and create your own docker images
• How about two-phased Docker image, one step will build the modular JRE, second will
package your .jar with it?

Two-phase dockerfile example
FROM solita/jdk10 as packager
# First stage: JDK 10 with modules required for Spring Boot
RUN /opt/jdk-10/bin/jlink
--module-path /opt/jdk-10/jmods
--verbose
--add-modules
java.base,java.logging,java.xml,jdk.unsupported,java.sql,java.naming,java.desktop,java.management,java.secu
rity.jgss,java.instrument
--compress 2
--no-header-files
--output /opt/jdk-10-minimal
# Second stage, add only our custom jdk9 distro and our app
FROM solita/jdk10
COPY --from=packager /opt/jdk-10-minimal /opt/jdk-10-minimal
COPY target/*.jar /opt/
ENV JAVA_HOME=/opt/jdk-10-minimal
ENV PATH="$PATH:$JAVA_HOME/bin"
EXPOSE 8080
CMD java -jar /opt/*.jar

Exercise resources
• https://github.com/crystoll/spring-boot-java10/
• https://hub.docker.com/r/solita/jdk10/
• https://hub.docker.com/r/solita/jdk11-ea/
• http://dev.solita.fi/2018/01/24/Java9-modules-Spring-Boot-2-Docker.html
• http://dev.solita.fi/2018/03/02/Update-to-Java11.html

Other Resources
• https://hub.docker.com/_/openjdk/
• https://hub.docker.com/r/solita/jdk10/
• https://stackoverflow.com/questions/48204141/replacements-for-
deprecated-jpms-modules-with-java-ee-apis/
• https://blog.frankel.ch/migrating-to-java-9/1/
• https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-with-Java-9
• https://github.com/dsyer/spring-boot-java-9

Hackathexerciseon
• Let’s try to build something with all this
• Idea: API for registering thumbs up/thumbs down signals for presentation
• Presentations have a name, and we register thumbs-up/thumbs-down entries for them
• Let’s assume presentations have shorter code that can be used to refer to it.
• Anyone can give as many entries as they like, not limited in this exercise
• API should also let us know total number of thumbs-up/thumbs-down for a presentation, and could
let us know most highly/lowly rated presentations
• Extra exercise:
• Simple UI for pressing thumbs-up/thumbs-down for a presentation
• Another UI for showing outcomes
• Websockets, real-time tracking of +/-
• CI pipeline, AWS Fargate/EKS deployment, self-healing capabilities, go crazy

Hackathexerciseon
• So, form small groups, experiment with either larger challenge or some
substeps
• Pull JDK10 docker image, or install JDK 10 locally, try jshell, jlink, syntax
• Create Spring Boot 2.0 initializr project, compile and run with JDK 10
• Create some API and Services, to push it further. Include db?
• Minimize the JDK 10 environment, see if it still runs. How are the resources doing? Can
you measure them? Can you compare them?
• Ask questions, try things, break things

Thanks!
ARTO SANTALA
Software Architect
arto.santala@solita.fi
+358505747452

Leaner microservices with Java 10

Leaner microservices with Java 10

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