October 2020 – World Of Nubcraft

Can’t copy text from webpage?

Sometimes I come upon a website that I cannot copy text from a HTML web page. Simply cannot click and highlight the lines I try to select for copying. I thought that my browser/mouse was not working. But I go to other sites, I am able to highlight/copy normally. They must’ve done something on that page probably to prevent content from being lifted of the page easily?

Why is this and how do they do it? Is this a javascript in the page that prevents me from copying?

ANSWER

Could be a script on the webpage. I’m certain that can be done or already been done through Javascript before.

I know that the same effect can be achieved via CSS alone. It is easier, cleaner and does not add to another Javascript messing up or slowing down a site. I prefer this method over the other.

Below are the CSS lines that does what you want. Different ones for different browsers. It is vendor specific for some, but does the same exact thing.

   user-select: none; /* Supported by Chrome, Firefox & Opera */
  -moz-user-select: none; /* Firefox (older) */
  -ms-user-select: none; /* Edge */
  -khtml-user-select: none; /* Konqueror */
  -webkit-touch-callout: none; /* Safari for iOS */
  -webkit-user-select: none; /* Safari for Mac */

Try it out. You can make it for entire page/site.

* {
     /* CSS lines go here */
}

Or you can make it so only targeted content will have it using Class or ID selectors.

#text-no-select {
     /* ID selector -  CSS lines go here */
}

.text-no-select {
     /* Class selector -  CSS lines go here */
}

Be aware this does not totally prevent anyone from copying content on a website. There are many other ways to go around this or even with a Javascript impementation. It is a minor roadblock.

How to make IntelliJ check and create SerialVersionUID

When the class implements Serializable I want the serialVersionUID field to be auto-created by IntelliJ IDE. This feature comes in automatically in Eclipse. But the former does not.

How do I make IntelliJ create the field or warn me that it is not defined in the class yet?

ANSWER

It is not turned on by default in IntelliJ. Can be easily done by going to the following:

File > Settings > Editor > Inspections > Java > Serialization Issues

Then find and select – Serializable class without ‘serialVersionUID’ – by checking on the box to the right of it.

Similarly, you can search for it once in File > Settings. Keyword for search can be – ‘serialVersionUID’ – without the quotes.

The path or location of this feature on IntelliJ may vary. It should be the same on Linux and Windows for versions 2019 and 2020.

This will only throw a warning. It does not magically create the field in all those classes that implements Serializable straight away. But then IntelliJ will help you create it, like any other decent IDE out there. Go to the class name declaration, you may find that it is subtly highlighted in yellow to hint that there is a user action that can be done. Hover then click on the option – Add ‘serialVersionUID’ field – and you will get the desired result like this one:

private static final long serialVersionUID = 6265605531073886420L;

Database tables map One To Many without foreign key in @JoinColumn

Possible to not have foreign key relationship in child table to its parent in the database, while in JPA it will still be able to map out fine? How will this be done?

Can I still use @JoinColumn to define the field for reference back to the parent table?

This is a one-to-many relationship. One parent record, many child records.

I only care about writes to the database tables right now.

ANSWER

Yes, no FKs defined in the database is fine. JPA will still be able to map out there relationships as defined in your entity classes.

In fact, enabling – spring.jpa.generate-ddl – in your application properties file will create the necessary Foreign Key and/or Unique Key constraints in the database. This is vendor dependent however.

For a One To Many relationship, it is straightforward to do. Example below definition below:

    @OneToMany(cascade = CascadeType.ALL)
    @JoinColumn(name = "recommendation_id")
    private List<CommentEntity> commentList;

This will map out the entity object values to the Comment table, assuming that is the name of the target table. Each one will be persisted to the child table along with the ID of the parent Recomendation under the recommendation_id column.

How to ignore unknown fields when parsing JSON using Jackson

In Java, there is Jackson 2 library that is very popularly used when reading JSON objects and mapping those values out to a POJO.

Happy path, as long a I have all the fields from the JSON defined in the POJO then okay. In a perfect world it will work 100%.

But there is no perfect world. The JSON object in other scenarios can contain unknown fields. These are not in my POJO. Application fails from reading that JSON to POJO.

Getting this error:

Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "status" (class com.example.dto.Evaluation), not marked as ignorable (6 known properties: "Book",

ANSWER

Use this Jackson annotation at a class level. This has to be configured per class. That should do it. Will ignore any unknown properties silently including nested objects.

@JsonIgnoreProperties(ignoreUnknown = true)

When you are using Jackson ObjectMapper directly, that can be configured to ignore unknown properties globally as well.

ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);

How Do I Decode An OpenShift Secret In A Mounted Volume?

Mounting an OpenShift Secret to its own volume is straightforward. There are plenty of examples on how to do it. The Web is littered with examples. Next, the most common thing any manual, guide or tutorial would say is to encode the secret in Base64.

For example I have a SSL certificate stored in a Java KeyStore file format or JKS. The recommended way is to store it in a Secret instead of ConfigMap since it is sensitive information. Of course, that goes without saying the JKS file is password-protected.

Second, it must be as a Base64 string before I save it as OpenShift Secret.

How do I get the Base64 string to be decoded in the mounted volume? This one does not seem to get many answers.

Do I need to include shell commands to decode it and write it to a folder?

Which folder should I write it to as best practice?

ANSWER

#1 The encoded JKS Secret as an environment variable

This is an option but I’m not a fan of it. The JKS file when encoded can become very long, especially when the file size is large. I don’t think environment variables were meant to be used like this – hold very long text values. That said, this is an easier implementation.

Map out the secret as an env var in OpenShift or Kubernetes. Then you can use that env var to echo the value and write it out to a file.

echo -n $SECRET_JKS_VAR | base64 --decode > /file/path/to/decoded-secret.jks

#2 Mount for read, mount for write

You have the secret mounted to a file path. That is for reading. Now you need to decode, which means writing to a file so your application can read it back unencoded.

First, define a mount point as and empty directory. It must be writable. Then make it memory only.

Next, read the JKS file from its mount point, write it out to the empty dir mount point.

cat /mount/file/path/for-reading/encoded-secret.jks | base 64 --decode > /mount/file/path/for-writing/decoded-secret.jks

I like this approach better. It makes more sense rather than mapping a very long base64-encoded text value as an environment variable. The caveat is here is slightly more configurations to be made. Also if I’m not mistaken the in-memory volume count against your app memory quota. Should be negligible unless you write thousands of files into it.

#3 Lastly, write where you can

Underneath that container is a file system. Where you have permission to write, then do so there. If it’s Linux, then this decision is pretty much arbitrary IMHO. Put it in /tmp or /home or /mnt. Security wise, others might have access to your app’s pod, that means they can get to the Secret as well. But that is another topic.