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Extremely Serious

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Squashing Commits Before Pushing a Branch into a Git Upstream

July 3, 2019 / / 0 Comments

Pre-requisite

  • Git is installed locally.

Procedures

  1. Checkout the non-master branch to be squashed.
  2. Ensure that the branch is up to date from the master.
  3. Open a terminal and change the directory to the root of checked out branch.
  4. Run the following command: 
    git rebase -i master
  5. Once a text editor opens and leave the first pick alone and the subsequent picks must be replaced with squash. For example:
    From

    pick < hash1 > < message1 >
pick < hash2 > < message2 >
pick < hash3 > < message3 > 
pick < hash4 > < message4 >

    To

    pick < hash1 > < message1 >
squash < hash2 > < message2 >
squash < hash3 > < message3 > 
squash < hash4 > < message4 >
  6. Save the update and close the editor.
  7. Another editor will open to update the message since git is about the combine multiple commits.
  8. Update the message if necessary.
  9. Save and close the editor.
  10. If everything went fine your branch is now squashed.

Sample Usage of Java 9 Flow (Reactive Stream) API

June 7, 2019 / / 0 Comments

Reactive stream is gaining traction in the mainstream programming and java has its own implementation via the Flow API. Popular reactive stream implementations are RxJava, Reactor and Akka.

import java.util.concurrent.Flow;
import java.util.concurrent.SubmissionPublisher;
import java.util.stream.IntStream;

public class Main {

    /**
     * Sample subscriber implementation.
     */
    public static class Subscriber implements Flow.Subscriber<Integer> {

        /**
         * Holds an instance of Flow.Subscription instance so that we can request what we can handle.
         */
        private Flow.Subscription subscription;

        /**
         * Tracks if the publisher was closed.
         */
        private boolean isDone;

        /**
         * Triggered on the initial subscription.
         * @param subscription An instance of Flow.Subscription.
         */
        @Override
        public void onSubscribe(Flow.Subscription subscription) {
            System.out.println("Subscribed");
            this.subscription = subscription;
            this.subscription.request(1);
        }

        /**
         * Do the actual processing.
         * @param item The actual item currently being processed.
         */
        @Override
        public void onNext(Integer item) {
            System.out.println("Processing " + item);
            this.subscription.request(1);
        }

        /**
         * Holds how to handle error.
         * @param throwable An instance of Throwable.
         */
        @Override
        public void onError(Throwable throwable) {
            throwable.printStackTrace();
        }

        /**
         * Called with the publisher was closed or completed.
         */
        @Override
        public void onComplete() {
            System.out.println("Processing done.");
            isDone = true;
        }
    }

    public static void main(String[] args) throws InterruptedException {
        
        //The publisher of the data.
        SubmissionPublisher<Integer> publisher = new SubmissionPublisher<>();

        //The sample subscriber implementation.
        Subscriber subscriber = new Subscriber();
        
        //Register a subscriber.
        publisher.subscribe(subscriber);

        //The sample stream to process.
        var intData = IntStream.rangeClosed(1, 10);

        //Publish the stream data. 
        intData.forEach(publisher::submit);

        //The publisher is done.
        publisher.close();

        //Since this is processing is asynchronous wait for everything to be processed. 
        while(!subscriber.isDone) {
            Thread.sleep(10);
        }
        
        System.out.println("Done");
    }
}

Resetting sa password in SQL Server Express

May 6, 2019 / / 0 Comments
  1. Open the Services application and look for SQL Server (SQLEXPRESS).
  2. Stop the SQL Server (SQLExpress) service.
  3. Right-click the SQL Server (SQLExpress) service and select Properties.
  4. At the Start parameters field type in -m.
  5. Click the Start button.
  6. Close the Services application.
  7. Open a Command Prompt in elevated mode.
  8. Execute the following command: 
    osql -S <LOCAL_PC_NAME>\SQLEXPRESS -E

    Note: The <LOCAL_PC_NAME> must be changed appropriately.

  9. At the prompt generated by the previous command invoke the following commands in sequence: 
    sp_password NULL,'<NEW_PASSWORD>','sa'

    Note: Change <NEW_PASSWORD> to your desired password.

    go
    quit
  10. Close the  elevated Command Prompt.
  11. Repeat steps 1 to 6, but on step 4 remove -m  from the Start parameters field, if it exists.

Configuring Archiva with MariaDB in Synology Diskstation

May 1, 2019 / / 3 Comments
  1. Install Tomcat 7 package in Diskstation
  2. Download archiva war file from the following address: 
    https://archiva.apache.org/index.cgi
  3. Place the downloaded war file (e.g. apache-archiva-2.2.3.war) into the following directory: 
    /volume1/@appstore/Tomcat7/src/webapps/
  4. In MariaDB, add the following user with appropriate password. 
    archivauser

    and the following database

    archiva
  5. Download the following jar files: 
    mail-1.4.jar 
mariadb-java-client-1.5.x.jar
  6. Place the download jar files in the following directory: 
    /volume1/@appstore/Tomcat7/src/lib
  7. Create archiva.xml file in the following location: 
    /volume1/@appstore/Tomcat7/src/conf/Catalina/localhost

    Add the following entries:

    <?xml version="1.0" encoding="UTF-8"?>
<Context path="/archiva" docBase="/volume1/@appstore/Tomcat7/src/webapps/<ARCHIVA_WAR_FILENAME>">
<Resource name="jdbc/users" auth="Container" type="javax.sql.DataSource"
	username="archivauser"
	password="<PASSWORD_HERE>"
	driverClassName="org.mariadb.jdbc.Driver"
	url="jdbc:mariadb://<MARIADB_HOST_IP>:<MARIADB_HOST_PORT
	/archiva?autoReconnect=true" />
<Resource name="mail/Session" auth="Container" 	type="javax.mail.Session" mail.smtp.host="localhost"/>
</Context>

    Note: The <ARCHIVA_WAR_FILENAME>, <PASSWORD_HERE> <MARIADB_HOST_IP> and <MARIADB_HOST_PORT tokens must be replaced by the downloaded war file from step 2, password used from step 4, IP address of MariaDB and port used by MariaDB repectively.

  8. Access archiva using the following address: 
    http://<DISKSTATION_HOST_IP>:7070/archiva

    Note: Update the token <DISKSTATION_HOST_IP> with the IP of your Synology Diskstation.

Configuring Tomcat 7 Package in Synology Diskstation

April 30, 2019 / / 2 Comments
  1. Install Tomcat 7 package.
  2. Edit the following file: 
    /volume1/@appstore/Tomcat7/src/conf/tomcat-users.xml
  3. Add the following entries: 
    <role rolename="manager-gui"/>
<user username="admin" password="<PASSWORD_HERE>" roles="manager-gui"/>

    Note: Update the token <PASSWORD_HERE> appropriately.

  4. Access the manager-gui using the following address format: 
    http://<DISKSTATION_HOST_IP>:7070/manager/html

    Note: Update the token <DISKSTATION_HOST_IP> with the IP of your Synology Diskstation.

Using JShell for testing an API

March 25, 2019 / / 0 Comments

Java 9 was released and JShell (i.e. The REPL of Java) is now real and we can use this to test an API.

For example if we want to check the reverse function StringUtils from the commons-lang3-3.1.jar.
1.) Using windows terminal (i.e. cmd command).
2.) From this directory execute to following command jshell command.
jshell --class-path .\commons-lang3-3.1.jar
Expect to see something similar to the following:
Welcome to JShell -- Version 9.0.1
For an introduction type: /help intro

jshell>
3.) From the jshell prompt import the class org.apache.commons.lang3.StringUtils just like we normally do in java and then press enter.
e.g.
jshell> import org.apache.commons.lang3.StringUtils
4.) To optionally check all the imported classes on the current jshell session we can use /imports command.
e.g.
jshell> /imports
The sample output would be:
|    import java.io.*
|    import java.math.*
|    import java.net.*
|    import java.nio.file.*
|    import java.util.*
|    import java.util.concurrent.*
|    import java.util.function.*
|    import java.util.prefs.*
|    import java.util.regex.*
|    import java.util.stream.*
|    import org.apache.commons.lang3.StringUtils
5.) Since we know that the StringUtils class was already loaded. We can now execute its reverse function.
e.g.
jshell> StringUtils.reverse("abcde")
The output must be:
$2 ==> "edcba"
Note: if you want to exit jshell execute the /exit command.

Enable Windows Subsystem for Linux (WSL) and Install Linux Distribution

February 5, 2019 / / 0 Comments

If you want to install any Linux distributions for WSL ensure that the Microsoft-Windows-Subsystem-Linux optional feature is enabled using the following procedure:

  1. Open a PowerShell as Administrator and run the following (i.e. if it is not installed): 
    Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Windows-Subsystem-Linux
  2. Restart the computer when prompted.
  3. Open the Microsoft Store
  4. Search for the Linux distribution (e.g. Ubuntu) you like.
  5. Click it and the click the Install button.
  6. After finishing the installation search for it in the Start menu.

    Usually the newly installed application is at the top of the start menu.

Pushing files with More than 1MB in Size via HTTP in Git

January 14, 2019 / / 0 Comments

For some reason, you have files with more than 1MB in total size to push to git respository by HTTP. You might be surprised that you cannot do it. This is because by default, git only posts to remote server via HTTP protocol with a maximum of 1MB. To remedy this, increase the http.postBuffer to 500MB (i.e. if you have to send files with 500MB total size) on client side like the following:

git config --global http.postBuffer 524288000

Reference

https://mirrors.edge.kernel.org/pub/software/scm/git/docs/git-config.html

Capturing the Output of a Command to a Variable

December 19, 2018 / / 0 Comments

Use the following for statement syntax with /f option

FOR /F ["options"] %variable IN (file-set) DO command [command-parameters]
FOR /F ["options"] %variable IN ("string") DO command [command-parameters]
FOR /F ["options"] %variable IN ('command') DO command [command-parameters]

    or, if usebackq option present:

FOR /F ["options"] %variable IN (file-set) DO command [command-parameters]
FOR /F ["options"] %variable IN ('string') DO command [command-parameters]
FOR /F ["options"] %variable IN (`command`) DO command [command-parameters]

    file-set is one or more file names.  Each file is opened, read
    and processed before going on to the next file in file-set.
    Processing consists of reading in the file, breaking it up into
    individual lines of text and then parsing each line into zero or
    more tokens.  The body of the for loop is then called with the
    variable value(s) set to the found token string(s).  By default, /F
    passes the first blank separated token from each line of each file.
    Blank lines are skipped.  You can override the default parsing
    behavior by specifying the optional "options" parameter.  This
    is a quoted string which contains one or more keywords to specify
    different parsing options.  The keywords are:

        eol=c           - specifies an end of line comment character
                          (just one)
        skip=n          - specifies the number of lines to skip at the
                          beginning of the file.
        delims=xxx      - specifies a delimiter set.  This replaces the
                          default delimiter set of space and tab.
        tokens=x,y,m-n  - specifies which tokens from each line are to
                          be passed to the for body for each iteration.
                          This will cause additional variable names to
                          be allocated.  The m-n form is a range,
                          specifying the mth through the nth tokens.  If
                          the last character in the tokens= string is an
                          asterisk, then an additional variable is
                          allocated and receives the remaining text on
                          the line after the last token parsed.
        usebackq        - specifies that the new semantics are in force,
                          where a back quoted string is executed as a
                          command and a single quoted string is a
                          literal string command and allows the use of
                          double quotes to quote file names in
                          file-set.

For a very basic example, lets capture the result of the echo test to a variable. This can be done as follows:

for /f %I in ('echo test') do set OUTPUT="%~I"

Note: The echo test command here could be any executable command (e.g. executing a different batch or any executable file).

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