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Refactoring your code to Java
9 modules
Rabea Gransberger
(MEKO-S GmbH)
@rgransberger
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Рабеа Грансбергер
Rabea Gransberger
• Computer Science Diploma 2008
• Java Developer, Project Lead at MEKOS, Germany
• Organization Team JUG Bremen, JCrete, JAlba
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JPoint Moscow / Java 9 Refactoring (Rabea Gransberger @rgransberger)
By Karte: NordNordWest, Lizenz: Creative Commons by-sa-3.0 de, CC BY-SA 3.0 de,
https://commons.wikimedia.org/w/index.php?curid=35392837
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102: Process API Updates
110: HTTP 2 Client
143: Improve Contended Locking
158: Unified JVM Logging
165: Compiler Control
193: Variable Handles
197: Segmented Code Cache
199: Smart Java Compilation, Phase Two
200: The Modular JDK
201: Modular Source Code
211: Elide Deprecation Warnings on Import Statements
212: Resolve Lint and Doclint Warnings
213: Milling Project Coin
214: Remove GC Combinations Deprecated in JDK 8
215: Tiered Attribution for javac
216: Process Import Statements Correctly
217: Annotations Pipeline 2.0
219: Datagram Transport Layer Security (DTLS)
220: Modular Run-Time Images
221: Simplified Doclet API
222: jshell: The Java Shell (Read-Eval-Print Loop)
223: New Version-String Scheme
224: HTML5 Javadoc
225: Javadoc Search
226: UTF-8 Property Files
227: Unicode 7.0
228: Add More Diagnostic Commands
229: Create PKCS12 Keystores by Default
231: Remove Launch-Time JRE Version Selection
232: Improve Secure Application Performance
233: Generate Run-Time Compiler Tests Automatically
235: Test Class-File Attributes Generated by javac
236: Parser API for Nashorn
237: Linux/AArch64 Port
238: Multi-Release JAR Files
240: Remove the JVM TI hprof Agent
241: Remove the jhat Tool
243: Java-Level JVM Compiler Interface
244: TLS Application-Layer Protocol Negotiation Extension
245: Validate JVM Command-Line Flag Arguments
246: Leverage CPU Instructions for GHASH and RSA
247: Compile for Older Platform Versions
248: Make G1 the Default Garbage Collector
249: OCSP Stapling for TLS
250: Store Interned Strings in CDS Archives
251: Multi-Resolution Images
252: Use CLDR Locale Data by Default
253: Prepare JavaFX UI Controls & CSS APIs for
Modularization
254: Compact Strings
255: Merge Selected Xerces 2.11.0 Updates into JAXP
256: BeanInfo Annotations
257: Update JavaFX/Media to Newer Version of GStreamer
258: HarfBuzz Font-Layout Engine
259: Stack-Walking API
260: Encapsulate Most Internal APIs
261: Module System
262: TIFF Image I/O
263: HiDPI Graphics on Windows and Linux
264: Platform Logging API and Service
265: Marlin Graphics Renderer
265: Marlin Graphics Renderer
266: More Concurrency Updates
267: Unicode 8.0
268: XML Catalogs
269: Convenience Factory Methods for Collections
270: Reserved Stack Areas for Critical Sections
271: Unified GC Logging
272: Platform-Specific Desktop Features
273: DRBG-Based SecureRandom Implementations
274: Enhanced Method Handles
275: Modular Java Application Packaging
276: Dynamic Linking of Language-Defined Object
Models
277: Enhanced Deprecation
278: Additional Tests for Humongous Objects in G1
279: Improve Test-Failure Troubleshooting
280: Indify String Concatenation
281: HotSpot C++ Unit-Test Framework
282: jlink: The Java Linker
283: Enable GTK 3 on Linux
284: New HotSpot Build System
285: Spin-Wait Hints
287: SHA-3 Hash Algorithms
288: Disable SHA-1 Certificates
289: Deprecate the Applet API
290: Filter Incoming Serialization Data
292: Implement Selected ECMAScript 6 Features in
Nashorn
294: Linux/s390x Port
295: Ahead-of-Time Compilation
297: Unified arm32/arm64 Port
298: Remove Demos and Samples
261: Module System
282: jlink: The Java Linker
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Carola Lilienthal: It's all about the domain, honey!
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https://c2.staticflickr.com/4/3206
/2348940045_40482b7109_b.jpg
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Software Design
customer.service invoice.service
picture.service camera.service
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Modules
customer.service
invoice.service picture.service
camera.service
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Modules
• Low coupling
• "There is a limit to how many things a person can think about a once."*
• => Chunking
• High cohesion
• "Incoherent fragments are hard to understands as an undifferentiated soup."*
Chunking Example:
06042018
(8 digits, chunking limit 7)
*Domain Driven Design, Eric Evans
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Modules
• Low coupling
• "There is a limit to how many things a person can think about a once."*
• => Chunking
• High cohesion
• "Incoherent fragments are hard to understands as an undifferentiated soup."*
Chunking Example:
06 04 2018
(3 groups, chunking limit 7)
*Domain Driven Design, Eric Evans
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Java 8 Code
• In Packages
• In JARs
• Classloader ignores JARs: No Dependency Graph
• Linear Scan
• More than one version of a class?
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OTIS
• 155.159 LOC
• 42.528 Classes
• 3884 Packages
• 285 Plugins (aka Modules)
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At the Vet
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Java 8 JavaFX Sample Application
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Entities
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Customer
Pet
Visit
Invoice
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External Dependencies
• Commons Lang 3: ToStringBuilder
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My friend …
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Work Items
Cars
Brand Repair
Car Repair
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Vet Entities
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Customer
Pet
Visit
Invoice
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Car Repair Entities
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Customer
Pet
Visit
Invoice
Car
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Identifiy Modules
• Parts without cyclic dependencies
• Reminder: JARs can have cycles
• Tools
• Structure 101
• Sonargraph
• UML
• jQAssistant
• DTangler (https://github.com/jimbethancourt/dtangler)
• Degraph
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customer.service invoice.service
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Domain Driven Design
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If we had applied DDD for the example…
… it would be easy to split code along:
• Bounded Contexts
• and maybe Aggregates
• DDD Modules not same as Bounded Contexts
• think packages / namespaces
• Part III tells you more about refactoring to DDD
See also: http://dddcommunity.org
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DTangler
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DTangler
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Degraph
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Domain Layers
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Customer
Pet
Visit
Invoice
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Technical Layers
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Customer
Pet
Visit
Invoice
DB
Model UI
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1. Refactoring: Technical Layers
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customer
customer.
model
customer.
db
customer.
ui
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Technical Layers
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Customer
Pet
Visit
Invoice
DB
Model UI
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2. Analysis
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Java 9
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Java 9 Platform Module System (JPMS)
JSR 376: 25. Nov 2014 => Released 21.09.2017
• Reliable configuration: Replace Classpath (-Hell)
• Strong encapsulation: public != Public
• Scalable Java SE Platform (JEP 200: Modular JDK)
• Greater platform integrity: illegal-access for internal API
• Improved performance: No linear scans
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Java 9 Module Definition
src\module-info.java
module {
requires ;
exports ;
uses ;
provides with ;
}
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Module
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model ui
db
util
requires
module model {
exports db;
}
module ui {
requires model;
exports table;
}
table
CustomerTable
Customer
getCustomer()
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model ui
db
util
table
requires
module model {
exports db;
}
module ui {
requires model;
exports table;
}
Module
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Customer
Pet
Visit
Invoice
Car
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New Modules
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model
customer.model
visit.model
invoice.model
ui
customer.ui
visit.ui
invoice.ui
pet
pet.model
pet.db
pet.ui
vet
ui
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2. Refactoring: Create Modules
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• Warning: No Split-Packages allowed
model
customer
ui
customer
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Demo
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External Dependencies
Example: Commons Lang 3 (commons-lang3-3.7.jar)
• Check for Automatic-Module-Name in JAR
• META-INF/MANIFEST.MF
• Automatic-Module-Name: org.apache.commons.lang3
• => requires org.apache.commons.lang3;
• Otherwise use file name as module name
• requires commons-lang3;
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CustomerView
private Node createTabPane() {
TabPane tabPane = new TabPane();
tabPane.getTabs().add(createTab("Pets", createPetNode()));
tabPane.getTabs().add(createTab("Invoices", createInvoiceNode()));
return tabPane;
}
private Node
createPetNode() {
List pets = new PetDao().fetchPetsForCustomer(customer.getId());
PetTable table = new PetTable(pets, false) {
protected void onDoubleClick(Pet pet) {
replace(new PetView(customer, pet));
}
};
return table; }
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3. Refactoring: Resolve Dependencies
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ui
CustomerView
TabService
List
createTabs()
pet
PetTabService
List
createTabs()
PetTable
module ui {
exports service;
uses CustomerViewTabService;
}
module pet {
requires ui;
provides CustomerViewTabService
with PetCustomerViewTabService;
}
Service
Loader
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Demo
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4. Refactoring: Car Repair Shop
• de.rgra.car replaces de.rgra.pet
• de.rgra.vet.ui transformed to de.rgra.app
• New Service: ApplicationConfigurationProvider
• New: de.rgra.vet.app and de.rgra.car.app
• Implements ApplicationConfigurationProvider
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Demo
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Jigsaw Dependency Visualizer
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Deployment
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Compile
• Every module to its own folder/jar
%JAVA_9%\javac --module-path mods
--module-source-path "./*/src"
-d classes
-Xlint:exports
@sources.txt
%JAVA_9%\jar --create
--file mlib/vet/de.rgra.model.jar
-C mods/vet/de.rgra.model_05 .
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Compile
• dir /s /B *.java | find "." > sources.txt
• %JAVA_9%\javac -p mods
--module-source-path "./*/src"
-d classes
@sources.txt
• xcopy /s/Y "de.rgra.model_05/resources"
"classes/de.rgra.model_05"
• %JAVA_9%\jar --create
--file mlib/vet/de.rgra.model.jar
-C classes/de.rgra.model_05 .
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Run
• %JAVA_9%\java -p mods/vet
-m de.rgra.vet.app_05/de.rgra.vet.VetAppConfiguration
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JLink
• Java binaries and modules in one package
%JAVA_9%/jlink
--module-path %JAVA_9%\jmods;mlib;mlib/vet
--add-modules de.rgra.vet.app_05
--output vetapp
--launcher vet=de.rgra.vet.app_05/de.rgra.vet.VetAppConfiguration
run vetapp/bin/vet.bat
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Maven + Gradle
Build with Maven >= 3.5 und Gradle >= 4.2
https://github.com/rgra/java9-module-refactoring/tree/master/de.rgra.vet_05
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Summary
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Refactoring Steps
• Package Structure:
..
.
..
• Domain Driven Design / Design Patterns
1. Analyse dependencies
2. Identifiy / Create Modules
3. Move Code to new modules
4. Resolve Dependencies with Interfaces / Services
a) Duplicate code if you can't find a quick solution
5. Go to 1.
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https://i.ytimg.com/vi/RijScDMVQzQ/maxresdefault.jpg
"The only thing a big bang rewrite
guarantees is a Big Bang!"
(M. Fowler)
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OTIS - Experience
• New module created only on business need
• new customer
• new service provider
• From monolith to 283 plugins in 5 years
• Module boundaries
• Refactoring usually easy by using new interfaces
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Tipp
• Don't: Split up monolith completely into modules
• A lot of work
• Hard to test
• No benefit in use
• Better: Identifiy modules when needed
Like in our example to replace pet with card
• "The only thing a big bang rewrite guarantees is a Big Bang!"
(M. Fowler)
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Advantages: Modules vs. Monolith
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Advantages: Modular Monolith vs. Monolith
• Architecture reflected in modules with clear boundaries
• Chunking
• Hide public classes
• Replace single modules
• Module Path more robust than Classpath
• Tool Support: Which Dependencies are missing?
• Smaller deployable units
• Better (Startup-) Performance
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Related Talks tomorrow
• 12:15 From monolith to microservices (Nikolay Archakov)
• 14:00 Designing for modularity with Java modules (Sander Mak)
• 15:45 A craftsman’s guide to a clean architecture (Marcus Biel)
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Slides & Code: https://rgra.github.io
Twitter: @rgransberger (DM open)
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June 2018 September 2017