If you are reading this post then, probably, you need to execute your java app as a Linux service.
This can be done in 4 really easy steps
sudo nano /etc/systemd/system/MyFantasticJavaApp.service
it will open the nano editor. Add the following, changing the working directory and the User values based on your convenience
[Unit] Description=good old Java application [Service] User=root # The configuration file application.properties should be here: # change this with your workspace WorkingDirectory=/usr/local/javaproject/ #path to executable. #executable is a bash script which calls jar file ExecStart=/usr/local/javaproject/myBashFile SuccessExitStatus=143 TimeoutStopSec=10 Restart=on-failure RestartSec=5 [Install] WantedBy=multi-user.target
save the file (Ctrl-X, select Y(es) and press enter)
Now let’s create a script which will basically call our jar/war file.
This file has to be the one specified in previous service file (what we call in ExecStart value). So, let’s write:
sudo nano /usr/local/javaproject/myBashFileit will open (again) the nano editor. Add the following 2(two) lines, changing the port and the path to your jar/war file
#!/bin/sh
sudo /usr/bin/java -Dserver.port=7080 -jar /usr/local/javaproject/MyFantasticJavaApp.jarsave the file (Ctrl-X, select Y(es) and press enter)
this is the simpler step. Just write this, changing the file and his path:
sudo chmod u+x /usr/local/javaproject/myBashFilesudo systemctl daemon-reload
sudo systemctl enable MyFantasticJavaApp.service
sudo systemctl start MyFantasticJavaAppEt voila! Do not thank me!
right click –> Source –> generate toString() –> Generated code fieldset –> Edit button –> New.. button –> give a name (ex. JSON) –> copy and paste this pattern:
{"${member.name()}":"${member.value}", "${otherMembers}"}
That’s it.
Hope this help!
In Java, as well as in your life, there two type of exception:
As in the life, for the expected events you are prepared because you plain to have that problem. So you are organized to intercept and block that problem. For example, if you are a student, or you have been a student, you know that your teacher could exam you. To avoid a negative
vote, or problem with you parents , you (theoretically) study. If you don’t study enough you could have a bad vote. But basically you are aware.
In Java is exactly the same, apart from the fact that problems are named Exception. You, and also the compiler, know that you can expect an exception calling a method and then you prevent that exception intercepting it with a try-catch-finally block.
int vote;
try{
vote=teacher.exams(you);
}
catch(NoStudiedException nse){
vote=VOTE.Very_Bad;
}
finally{
register.setVote(you,vote);
}
In Java you are aware because exists the throws clause that forces you to face up to your problem.
The exams method of Teacher class is like below:
public int exams(Student student) throws NoStudiedException{
…
}
But, unfortunately, there are no just checked exception. We can have also unexpected exception that you and the compiler are not aware, for example RuntimeException, ArrayIndexOutOfBoundException, but above all: NullPointerException.
They are all problems you could never have imagined it could happen to you. They are Unchecked.
All exception under Error and RuntimeException classes are Unchecked
You have to know the difference even because there are some framework that have different behavior based on checked and unchecked events.
For example JPA, that is in charge of transactions, makes an automatic rollback just in case of unchecked exception, BUT doesn’t make the same for the checked ones. It means that, if you use JPA and you want rollback when a CheckedException happens, then you have manually rollback out, adding the clause “rollbackFor=<CheckedException>.class” above the method. If you don’t use JPA and his children/nephew then pretend I did not say anything…
A domain, in weblogic world, is a set of weblogic (WL) instances that can be managed by the same administration console.
That’s why they are call managed servers.
Each WL instance can run on the same machine of the administration server or remotely
It is just an ip and port address where the single weblogic listen
If you have different weblogic servers that you need to manage (remotely for example) you can create a domain that includes them.
Or/And, if you need a cluster of instances then you must before add all cluster instances in a domain and then you can create your cluster
So you can have two types on WL instances in a domain: Standalone (which don’t belong to any cluster) and Clustered
In weblogic console, in Environment==> Servers you can add you weblogic instances. You have just to know the ip and port address of each weblogic instance you want to add in the domain
A cluster is a subset of a weblogic domain, where each WL instance of the cluster has the same goal: allow load balancing and fail over for the fantastic (same) applications they host.
Of course, as you manage a set of instance for the same application(s), when you deploy the application you do it just one time for all WL instance in the cluser, and the WebLogic Administration is in charge of update all instances in the cluster.
Just a thing good to know: all the WL in a cluster must have the same WL version
From a client point of view the cluster is transparent. The client doesn’t know how many WL instances there are behind that ip address
Advantages of a cluster are the same of LoadBalancing and Failover.
Scalability (Load Balancing): The capacity of an application deployed on a WebLogic Server cluster can be increased dynamically to meet demand. You can add server instances to a cluster without interruption of service, the application continues to run without impact to clients and end users.
High-Availability (Failover): In a WebLogic Server cluster, application processing can continue when a server instance fails. You “cluster” application components by deploying them on multiple server instances in the cluster so, if a server instance on which a component is running fails, an other server instance on which that component is deployed can continue application processing.
You can manage WL instances for a cluster in just two steps:
That’s it!
To debug with eclipse to remote server follow below instructions
In the menu Run –> Debug configurations…
In the window popup select Remote Java Application
Right click, then select New
On the right a new fieldset appears
In the Project field browse the java project to attach
In the Connection Type field:
The listening port, in both case (local and remote), must be preconfigured setting, as jvm parameters, the following:
-Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,address=4000
The JDWP protocol is the protocol used to debug with a remote debugger.
For example, in WebLogic server, to allow a debug socket listener, in the file “startWebLogic.cmd” add to the JAVA OPTIONS:
set JAVA_OPTIONS=-<others params> Xdebug -Xnoagent -Xrunjdwp:transport=dt_socket,address=4000,server=y,suspend=n
The -Xnoagent parameter disables the default sun.tools.debug debug agent
Just a little notice: if you want to debug clustered application, you have to attach the debug ide to all clustered servers, otherwise you need to be lucky to get the request to your debugged server
Curiosity: default debug port on weblogic 12.1.3 is 8453
The label in Java (from version 7) is a way of giving a logic name to a loop statement.
Why naming a statement in Java?
Just because in case, of very deeper loops, you want to break/continue that specific statement.
How to give a name to a statement?
Specifying a name (as a class style) followed by “:”
How can you break using label?
Simple, with break and continue followed by the label name. That’s it.
Example
Task:
{
(loop statement){
if (condition){
break Task;
}
}
}In the above example “Task” is the label. When you reach the line “break Task;” the program will go outside the Task statement.
Of course the similar logic works with “continue Task;“, but in this case the program will continue with labeled statement.
A little curiosity, the below code works perfectly:
public int myMethod(){
http://www.google.com
return 1;
}
because “http:” is treated as label and “//www.google.com” is treated as comment