Java9 hacks, tips & tricks
Here I will be sharing any useful information I get around Java9.
Java9 is not new one anymore but still we are yet pending to change our mindsets to think in functional way since Java8.
People/recruiters are still not ready to accept that their 90% work force is still living in OOP world. And believe it or not, this thought process change is required at the organisation level & if you don't set your priorities correct & don't understand your requirements properly then in next few months you will be sitting on the pile of mess of yours only.
https://www.baeldung.com/java-9-modularity
Well, during checking reactive APIs/streams, I was trying to use reactivex API, a 3rd party API to check one example.
But since Java9 being a modular one, I was not getting the way to use the 3rd party API.
So I searched on Google & I got the below answer on - stackoverflow
And the same solution can be used to include other 3rd party APIs.
Use the command on command prompt for the library you want to include & like shown in below images also -
jar --file reactive-streams-1.0.2.jar --describe-module
Java9 is not new one anymore but still we are yet pending to change our mindsets to think in functional way since Java8.
People/recruiters are still not ready to accept that their 90% work force is still living in OOP world. And believe it or not, this thought process change is required at the organisation level & if you don't set your priorities correct & don't understand your requirements properly then in next few months you will be sitting on the pile of mess of yours only.
https://www.baeldung.com/java-9-modularity
Well, during checking reactive APIs/streams, I was trying to use reactivex API, a 3rd party API to check one example.
But since Java9 being a modular one, I was not getting the way to use the 3rd party API.
So I searched on Google & I got the below answer on - stackoverflow
And the same solution can be used to include other 3rd party APIs.
Use the command on command prompt for the library you want to include & like shown in below images also -
jar --file reactive-streams-1.0.2.jar --describe-module
Now you need to include the name in the like having 'automatic' in above output for any library you want to use. like shown below. Include this in 'module-info.java' of your Java9 project, to make this library available to your code.
If you have watched above video or knows about the new features in Java9, then you know that you can create you own lightweight JRE to execute your code rather carrying the whole default JRE.
For this jlink is provide from java9, but for this you need to follow some steps first, like shown below.
I have project which requires another module, so either assume it or you can create such project.
Now -
First we need to compile module-info.java & copy the jar file of the required module at one place & refer that path via -p & I have put this jar at the same place so using '.' -
javac -p . -d e:\out module-info.java
Second, we need to compile the java files so that required modules are available like in above step -
javac -p . -d e:\out test\Testing.java
Third & final step, we need to generate the custom JRE required to execute our application, so we need to make sure all the required modules are available in our custom JRE. Use command like as shown below -
jlink --module-path "%JAVA_HOME%\jmods\java.base.jmod";e:\out;. --add-modules check --output e:\out\customJRE
Note : I have used j.base.jmod only from java as I will need only that module only to run my class, you can just mention a list of modules separated by ';' like I did above to include my module from e:\out
--add-modules give the name of the module for your application, like I have 'check'
--output, using this to give the path where you want to generate your JRE, like I did for customJRE
So your JRE will be generated at the given path which will be having all the required dependencies to execute your application. Though it reduces the size of JRE but still I didn't see the excpected size reduction, as JRE is still bulky.
But anyhow you can try try this way. In case of issues follow online docs or let me know the issue.
For this jlink is provide from java9, but for this you need to follow some steps first, like shown below.
I have project which requires another module, so either assume it or you can create such project.
Now -
First we need to compile module-info.java & copy the jar file of the required module at one place & refer that path via -p & I have put this jar at the same place so using '.' -
javac -p . -d e:\out module-info.java
Second, we need to compile the java files so that required modules are available like in above step -
javac -p . -d e:\out test\Testing.java
Third & final step, we need to generate the custom JRE required to execute our application, so we need to make sure all the required modules are available in our custom JRE. Use command like as shown below -
jlink --module-path "%JAVA_HOME%\jmods\java.base.jmod";e:\out;. --add-modules check --output e:\out\customJRE
Note : I have used j.base.jmod only from java as I will need only that module only to run my class, you can just mention a list of modules separated by ';' like I did above to include my module from e:\out
--add-modules give the name of the module for your application, like I have 'check'
--output, using this to give the path where you want to generate your JRE, like I did for customJRE
So your JRE will be generated at the given path which will be having all the required dependencies to execute your application. Though it reduces the size of JRE but still I didn't see the excpected size reduction, as JRE is still bulky.
But anyhow you can try try this way. In case of issues follow online docs or let me know the issue.
Be cautious about using 'Transitive' dependency in Java modules, as you can be on some slippery slope towards many modules.
98 modules are made from that single rt.jar
Creating Multi release jar-
Multi-Release Jar Files | Baeldung
Multi-Release Jar Files | Baeldung
Get more details about the modules in Java-
Java Modules (jenkov.com)
A Guide to Java 9 Modularity | Baeldung
Java Modules (jenkov.com)
A Guide to Java 9 Modularity | Baeldung
Java Flight Recorder
Monitoring Java Applications with Flight Recorder | Baeldung
What is Java Mission Control and how does it work? (theserverside.com)
Oracle Java Mission Control: The Ultimate Guide (overops.com)
Monitoring Java Applications with Flight Recorder | Baeldung
What is Java Mission Control and how does it work? (theserverside.com)
Oracle Java Mission Control: The Ultimate Guide (overops.com)
Do we need Cleaner? Who needs Cleaner?
Check once the usage of Cleaner - What is the use of the Cleaner class in Java 9? (tutorialspoint.com)
And I agree that finalize() was not effective, though I don't think it as a mistake like it is told by many people.
It needs to be understood first, before you start pushing your expectations to it.
But anyhow, it is deprecated & another class Cleaner was introduced, but still I see the scope is very specific.
It still has one issue that if an object is having the opened connection to some external DB & that object was reachable but not used in the program till the end & program shuts properly then who will be cleaning those connections?
So if in any such cases we need to take the responsibility then better use ShutDownHooks as shown here.
And I agree that finalize() was not effective, though I don't think it as a mistake like it is told by many people.
It needs to be understood first, before you start pushing your expectations to it.
But anyhow, it is deprecated & another class Cleaner was introduced, but still I see the scope is very specific.
It still has one issue that if an object is having the opened connection to some external DB & that object was reachable but not used in the program till the end & program shuts properly then who will be cleaning those connections?
So if in any such cases we need to take the responsibility then better use ShutDownHooks as shown here.
