Guide: To JAR Hell and Back

Show that it works on Java 8:

mvn -v
mvn clean verify
java -cp 'app/*' monitor.Main

In a different terminal:

curl http://localhost:4567/stats/xml
watch -n 1 curl http://localhost:4567/stats/xml

Migration

Building on Java 9

start building with Java 9
1. show mvn -v
2. sdk use java jdk-9
3. show mvn -v

create a profile for Java 9+

<profiles>
	<profile>
		<id>java-9+</id>
		<activation>
			<jdk>[9,)</jdk>
		</activation>
	</profile>
</profiles>

set release to 9 in profile

<properties>
	<maven.compiler.release>9</maven.compiler.release>
</properties>

Internal APIs

mvn clean verify

fix use of sun.misc.BASE64Encoder

Base64.getEncoder().encodeToString(content.getBytes());

note warning message in monitor.utils

fix warning messages in UtilsTest in monitor.utils

create a profile for Java 9
show that illegal-access=deny disallows access

configure Surefire to use --add-opens

<build>
	<plugins>
		<plugin>
			<artifactId>maven-surefire-plugin</artifactId>
			<configuration>
				<argLine>
					--illegal-access=deny
					--add-opens=java.base/java.lang=ALL-UNNAMED
				</argLine>
			</configuration>
		</plugin>
	</plugins>
</build>

better, yet: update Mockito to 2.8.47

Java EE Modules

note error package javax.xml.bind.annotation is not visible
1. open StatisticsEntity
add comment // from module java.xml.bind: above import XmlElement

add java.xml.bind module for annotations in monitor.rest

create a profile for Java 9

configure compiler to use --add-modules java.xml.bind to fix package javax.xml.bind.annotation is not visible

<build>
	<plugins>
		<plugin>
			<artifactId>maven-compiler-plugin</artifactId>
			<configuration>
				<compilerArgs>
					<arg>--add-modules=java.xml.bind</arg>
				</compilerArgs>
			</configuration>
		</plugin>
	</plugins>
</build>

Patch Modules

observe error: cannot find symbol for missing type Generated
1. open StatisticsEntity
add java.xml.ws.annotation to monitor.rest to fix missing type Generated
1. observe that error contains no hint of the containing module
2. look up module in documentation
3. add comment // from module java.xml.ws.annotation: above import Generated
4. add java.xml.ws.annotation
  <arg>--add-modules=java.xml.ws.annotation</arg>
5. observe new missing types problem

patch java.xml.ws.annotation with JSR classes

<arg>--patch-module=java.xml.ws.annotation=${settings.localRepository}/com/google/code/findbugs/jsr305/3.0.2/jsr305-3.0.2.jar</arg>

replace maven.compiler.release with maven.compiler.source and maven.compiler.target in parent POM

Running on Java 9

Start running with Java 9:

java --class-path 'app/*' monitor.Main

fix cast to URLClassLoader by replacing code in logClassPathContent with

String[] classPath = System.getProperty("java.class.path").split(":");
String message = Arrays.stream(classPath)
		.map(url -> "\t" + url)
		.collect(joining("\n", "Class path content:\n", "\n"));
System.out.println(message);

add module java.xml.bind

java --add-modules java.xml.bind --class-path 'app/*' monitor.Main

note that --add-exports, --add-opens, --add-modules, --patch-module usually carry from build to compile time

Using Java 10

update to 10 with sdk use java jdk-10
show mvn -v

limit parent POM profile for Java 9+ to 9 and copy paste to create one for 10

<profile>
	<id>java-10</id>
	<activation>
		<jdk>10</jdk>
	</activation>
	<properties>
		<maven.compiler.source>10</maven.compiler.source>
		<maven.compiler.target>10</maven.compiler.target>
	</properties>
</profile>

to use var somewhere, activate java-10 profile in IntelliJ and reimport
build with mvn clean verify
fix error in monitor.utils by updating Mockito to 2.18.3

in parent POM’s Java 10 profile update ASM to preempt compiler problems

<build>
	<plugins>
		<!-- if compilation fails, try newer version of ASM
				https://stackoverflow.com/q/49398894/2525313
		-->
		<plugin>
			<artifactId>maven-compiler-plugin</artifactId>
			<dependencies>
				<dependency>
					<groupId>org.ow2.asm</groupId>
					<artifactId>asm</artifactId>
					<version>6.1.1</version>
				</dependency>
			</dependencies>
		</plugin>
	</plugins>
</build>

run with

java --add-modules java.xml.bind --class-path 'app/*' monitor.Main

Using Java 11

update to 11 with sdk use java jdk-11
show mvn -v
in parent POM update compiler plugin to 3.8.0
remove ASM update in profile java-10

in parent POM copy paste profile to create one for 11

<profile>
	<id>java-11</id>
	<activation>
		<jdk>11</jdk>
	</activation>
	<properties>
		<maven.compiler.source>11</maven.compiler.source>
		<maven.compiler.target>11</maven.compiler.target>
	</properties>
</profile>

build with mvn clean verify
in monitor.rest's POM, show how to edit profile to only be active for 9, 10:
```
<id>java-9-01</id>
<activation>
	<jdk>[9,10]</jdk>
</activation>
```

then remove profile and add third-party dependencies in monitor.rest's POM:

<dependency>
	<groupId>javax.annotation</groupId>
	<artifactId>javax.annotation-api</artifactId>
	<version>1.3.1</version>
</dependency>
<dependency>
	<groupId>javax.xml.bind</groupId>
	<artifactId>jaxb-api</artifactId>
	<version>2.3.0</version>
</dependency>
<dependency>
	<groupId>com.sun.xml.bind</groupId>
	<artifactId>jaxb-core</artifactId>
	<version>2.3.0</version>
</dependency>
<dependency>
	<groupId>com.sun.xml.bind</groupId>
	<artifactId>jaxb-impl</artifactId>
	<version>2.3.0</version>
</dependency>

run with
```
java --class-path 'app/*' monitor.Main
```
observe that xml endpoint does not return anything, but json does
activate java-11 profile, reimport, and launch from IntelliJ
in MonitorServer change catch (JAXBException ex) to catch (Throwable ex) and observe the error

add this dependency:

<!-- HOW?! -->
<dependency>
	<groupId>com.sun.activation</groupId>
	<artifactId>javax.activation</artifactId>
	<version>1.2.0</version>
</dependency>

(Was not needed before because java.xml.bind requires it)

point out illegal access warning (if present) and replace all dependencies in monitor.rest with:

<dependency>
	<groupId>javax.annotation</groupId>
	<artifactId>javax.annotation-api</artifactId>
	<version>1.3.2</version>
</dependency>
<dependency>
	<groupId>javax.xml.bind</groupId>
	<artifactId>jaxb-api</artifactId>
	<version>2.3.1</version>
</dependency>
<dependency>
	<groupId>com.sun.xml.bind</groupId>
	<artifactId>jaxb-core</artifactId>
	<version>2.3.0.1</version>
</dependency>
<dependency>
	<groupId>com.sun.xml.bind</groupId>
	<artifactId>jaxb-impl</artifactId>
	<version>2.3.3</version>
</dependency>

Modularization

Preparation

in parent POM, replace compiler source and target 8 with release 11
remove version-specific profiles

Get an Overview

see artifact dependencies

jdeps -summary -recursive --class-path 'app/*' --multi-release 11 app/main.jar

limiting to Monitor classes

jdeps -summary -recursive --class-path 'app/*' --multi-release 11 -include 'monitor.*' app/main.jar

create a diagram

jdeps -summary -recursive --class-path 'app/*' --multi-release 11 -include 'monitor.*' --dot-output . app/main.jar
dot -Tpng -O summary.dot
gwenview summary.dot.png

clean up graph

sed -i '/java.base/d' summary.dot
sed -i 's/.jar//g' summary.dot
dot -Tpng -O summary.dot
gwenview summary.dot.png &

Start Bottom-Up

start with monitor.utils

modularize monitor.utils

module monitor.utils {
	exports monitor.utils;
}

build with Maven

observe that monitor.utils is module:

jar --describe-module --file app/utils.jar

observe that the module works on the class path:
```
java --class-path 'app/*' monitor.Main
```

make it work on module path

create move-modules.sh
```
#!/bin/bash
set -e

rm -rf mods
mkdir mods
```
and make it executable with chmod +x move-modules.sh
add mv app/utils.jar mods to move-modules.sh
create run.sh
```
#!/bin/bash
set -e
```

try to run

# fails
java --class-path 'app/*' --module-path mods monitor.Main
# too noisy
java --class-path 'app/*' --module-path mods \
	--show-module-resolution monitor.Main
# no utils
java --class-path 'app/*' --module-path mods \
	--show-module-resolution monitor.Main
| grep utils
# yes utils!
java --class-path 'app/*' --module-path mods \
	--add-modules monitor.utils \
	--show-module-resolution monitor.Main
| grep utils
# launch
java --class-path 'app/*' --module-path mods \
	--add-modules monitor.utils \
	monitor.Main

continue with observers

modularize monitor.observer:

module monitor.observer {
	exports monitor.observer;
}

modularize monitor.observer.alpha:

module monitor.observer.alpha {
	requires monitor.observer;
	exports monitor.observer.alpha;
}

modularize monitor.observer.beta:

module monitor.observer.beta {
	requires monitor.observer;
	exports monitor.observer.beta;
}

in monitor.observer.alpha, show with mvn -X compiler class/module path
add mv app/observer* mods to move-modules.sh

run

java --class-path 'app/*' --module-path mods \
	--add-modules monitor.utils,monitor.observer.alpha,monitor.observer.beta \
	monitor.Main

modularize statistics as preparation for monitor.rest

modularize monitor.statistics

module monitor.statistics {
	requires monitor.observer;
	exports monitor.statistics;
}

add mv app/statistics.jar mods to move-modules.sh

run

java --class-path 'app/*' --module-path mods \
	--add-modules monitor.utils,monitor.observer.alpha,monitor.observer.beta,monitor.statistics \
	monitor.Main

modularize monitor.rest in face of unmodularized dependencies

create initial module descriptor

module monitor.rest {
	requires java.xml.bind;

	requires monitor.utils;
	requires monitor.statistics;

	exports monitor.rest;
}

use jar11 --describe-module-file --file spark-core etc to determine module names
add requires for spark.core, jackson.core, jackson.databind to module descriptor
identify split package between jsr305 and java.annotation
add requires java.annotation

patch package split:

<build>
	<plugins>
		<plugin>
			<artifactId>maven-compiler-plugin</artifactId>
			<configuration>
				<compilerArgs>
						<arg>--patch-module=java.annotation=${settings.localRepository}/com/google/code/findbugs/jsr305/3.0.2/jsr305-3.0.2.jar</arg>
				</compilerArgs>
			</configuration>
		</plugin>
	</plugins>
</build>

add to move-modules.sh:

mv app/jaxb-api.jar mods
mv app/javax.activation.jar mods
mv app/javax.annotation-api.jar mods
mv app/spark-core.jar mods
mv app/jackson-core.jar mods
mv app/jackson-databind.jar mods

run

java --class-path 'app/*' --module-path mods \
	--add-modules monitor.rest,monitor.observer.alpha,monitor.observer.beta \
	monitor.Main

mention that --patch-module is not needed because annotations are not evaluated at run time
observe run-time error in watch tab
add opens monitor.rest to java.xml.bind; to monitor.rest

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guide.adoc

guide.adoc

Guide: To JAR Hell and Back

Migration

Building on Java 9

Internal APIs

Java EE Modules

Patch Modules

Running on Java 9

Using Java 10

Using Java 11

Modularization

Preparation

Get an Overview

Start Bottom-Up

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guide.adoc

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guide.adoc

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Guide: To JAR Hell and Back

Migration

Building on Java 9

Internal APIs

Java EE Modules

Patch Modules

Running on Java 9

Using Java 10

Using Java 11

Modularization

Preparation

Get an Overview

Start Bottom-Up