JavaScript is arguably the programming language out there, and specifically in terms of client-side programming languages, there are few alternatives to match it. Obfuscation involves deliberately creating source or machine code that is difficult for humans to understand, protecting the integrity of the initial programmers’ code. Programmers may deliberately obscure their code to protect its purpose or the implicit values embedded in it. This is primarily done to prevent tampering and reverse engineering. However, it is also important for those who sell their code, it is, unfortunately, easily copied. Obfuscating your JavaScript via Node.js does not prevent your code being copied, but certainly makes in hardly readable. Security through obscurity. Not only that, but Node.js is a language deriving from JavaScript, making the learning curve quite intuitive. Below we’ll go through the benefits and method of obfuscating JavaScript with Node.js.
Installing The Right Obfuscator
In order to get started, you need to install the JavaScript Obfuscator. This must be done before any JS code can be obscured with Node.js, as the process is reliant on the JS obfuscator module. It’s a powerful tool, with a wide array of features ensuring security for your source code. Limitless restrictions, local machine compatible, no server-data exchange, and compatible primarily with es2015 and es2016 makes it an intuitive and essential tool in protecting your code.
The logic to obfuscate code is relatively simplistic. It is capable of creating an instance of the Module, from which it is possible for you to use the obfuscate method that expects as first argument the code that you want to obfuscate. Through a series of transformations your source code is transformed into something obscure, and very difficult to read.
Process Logic
Given the popularity of JavaScript, using Node.js makes sense – particularly if you have experience working with JS on front-end applications, you will have an easy time learning Node.js for your backend applications. This makes your working environment more efficient as you are continuing to work in a relatively familiar environment.
Web Developer, Kuan-Yin T’an, of Dissertation Writer and OXEssays, suggests, “it’s really important to ensure that your workflow is compliments by the tools your using. Wasting time with other languages is inefficient, particularly given the complimentary benefits of Node.js with JavaScript. The system offers a wide variety of tools making a programmer’s life much easier – and in the end, that will only increase your output.”
Performance Positives
It is true that you are sure to find some high-performance power from using Node.js, but is important to dive into why this is the case. Node.js reads JavaScript code via Google’s V8 JavaScript engine – this engine is vital as it compiles the JS code right into the machine code. Essentially the code is implemented quicker and with greater efficiency. Additionally, the speed by which the code is executed is facilitated because of the runtime environment is support from non-blocking I/O operations.
Alanis Truijens, tech writer for AustralianHelp and Urgent Assignment Help, was clear in her own assessment, “The simplest version I can give is that Node.js functions as a JS runtime environment that allows JS coding to be executed in a server-side environment. At its core, this is an open-source platform which increases flexibility to get things done”.
Application Scalability
Using Node.js means that scaling your applications is relatively straight forward. Whether it is horizontal or vertical, it doesn’t matter, you can scale to your own needs. Additionally, it’s possible to add different resources to the single nodes when vertically scaling your applications.
Weighing It All Up
The reality is simple. Node.js has more advantages than disadvantages, and in terms of workflow it’s more efficient. What is notable about the disadvantages is that they all appear to be relatively fixable, when compared with other tools. Node.js uses JavaScript, which makes it a good system for back-end development given the intuitive learning curve. Finally, there are more businesses using Node.js, and that more than anything really makes it the complimentary system to use when obfuscating JavaScript.
When you build up an application, you need a database (db) to save your data. It could be about your order, member, or transactional data. It really depends on business needs from the application that you build. Another purpose is you can initiate improvements based on huge data that you’ve already saved.
Based on Wikipedia, a database is an organized collection of data, generally stored and accessed electronically from a computer system. Where databases are more complex they are often developed using formal design and modeling techniques Wikipedia.
There are many great databases these days, one of it is MySQL. In this section, we will learn from the beginning how to create a database, tables, and query data with MySQL.
Why MySQL:
It is open source. However, there are a personal and enterprise version.
Fast. Of course with the right indexes when you have huge amount of rows data.
Scalability, maintainability.
Suitable for web-based application. E-commerce, warehouse, logging, and many more.
Before we start, to create or manage your MySQL database, you need database client/IDE.
Personally, I find Sequel Pro is very helpful and powerful for my day to day use.
Start and Login to MySQL on your local machine (macOS X).
Go to your System Preferences
Find MySQL
Choose to Start MySQL Server
After the MySQL database started you can login.
Go to your database client, in this example I am using Sequel Pro.
Connect to your localhost. You need to provide the username and password before login.
Once you connect you will be able to create your database.
Create new Database:
Create Database Statements
CREATE DATABASE database_name
[[DEFAULT] CHARACTER SET charset_name]
[[DEFAULT] COLLATE collation_name];
Example:
CREATE DATABASE learning_mysql
CHARACTER SET utf8
COLLATE utf8_general_ci;
Using Functionality Provided by IDE
Go to Database menu, select Add Database…
Then fill in the database name
For common cases and non latin, use UTF-8 for character set and you can user utf8_general_ci for the collation.
Your database is now ready to use. Ensure you choose the right database that you want to manage. The second step is to prepare tables as per your business needs, to save the data from your application.
MySQL is an open-source RDBMS (Relational Database Management System). As the name implied it uses SQL (Structured Query Language) to access and manipulate data. MySQL has been widely used to store and manage data ranging from a simple web application to an enterprise class application.
The important of data in every application require us to regularly backup the data to prevent data loss, for example caused by hardware crashes. In this post I will show you how to backup the database manually and using a script combined with a cron job to run the process automatically.
Using mysqldump
To create a database backup in MySQL we can use the mysqldump command. The example syntax of using this command is:
If you need to restore the database you can use the following command:
mysql -u username -p database_to_restore < backup_file_name.sql
Before you can execute the command you might need to create the database if you don’t already have the it.
saturn@ubuntu:~$ mysql -u root -p
CREATE DATABASE database_to_restore;
exit;
Creating Backup Script
To start let’s create MySQL user account that we are going to use to do the backup process. Login to MySQL using mysql -u root -p command. Type and execute the following command to create backupuser.
grant lock tables, select, show view on kodejava.* to 'backupuser'@'localhost' identified by 'backuppasswd';
flush privileges;
Exit from the MySQL using the exit command and create the following backup script called backup.sh using your favorite editor. For example you can use nano or vim to create the file.
#!/bin/sh
BACKUP_HOME="/home/saturn/backup"
cd $BACKUP_HOME
directory="$(date +%Y%m%d)"
if [ ! -d "$directory" ]; then
mkdir $directory
fi
backupdir="$BACKUP_HOME/$directory"
backup="kodejava-$(date +%Y%m%d%H%M%S)"
mysqldump -ubackupuser -pbackuppasswd --opt kodejava > $backupdir/$backup.sql
cd $directory
tar -czf $backup.tar.gz $backup.sql
rm $backup.sql
To make the backup.sh file executable you need to run the chmod +x backup.sh command.
Creating Scheduler Using Crontab
The crontab command is used to schedule commands to be executed periodically at a predetermined time. It will run as a background process without needing user intervention. These kind of jobs is generally referred to as cron jobs and the jobs will run as the user who creates the cron jobs.
In the example below we register a cron job to execute the script at 12:00AM everyday. To edit the cron jobs type crontab -e, this will open the crontab file.
saturn@ubuntu:~$ crontab -e
no crontab for saturn - using an empty one
Select an editor. To change later, run 'select-editor'.
1. /bin/ed
2. /bin/nano <---- easiest
3. /usr/bin/vim.basic
4. /usr/bin/vim.tiny
Choose 1-4 [2]:
Select an editor to edit the crontab, choose by entering the number of the editor. The easiest one is nano but you can also use vim if you comfortable with it.
An you will see an empty crontab file will the following commented messages:
# Edit this file to introduce tasks to be run by cron.
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#
# To define the time you can provide concrete values for
# minute (m), hour (h), day of month (dom), month (mon),
# and day of week (dow) or use '*' in these fields (for 'any').#
# Notice that tasks will be started based on the cron's system
# daemon's notion of time and timezones.
#
# Output of the crontab jobs (including errors) is sent through
# email to the user the crontab file belongs to (unless redirected).
#
# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/
#
# For more information see the manual pages of crontab(5) and cron(8)
#
# m h dom mon dow command
Go to the end of the file and write the following entry to register a cron job. In the example below we register a cron job to execute the backup.sh script at 12:00M everyday.
# m h dom mon dow command
0 0 * * * /home/saturn/backup.sh
After you save the file you can use the crontab -l command to list the registered cron job. If you want to know more about crontab you can visit crontab guru website.
Java has been ranking as one of the most popular web programming languages for many years. In this tutorial on sending emails in Java, which was originally published on the Mailtrap blog, we will demonstrate how to build HTML emails with images and attachments and send them using an SMTP server.
The main option is to use a Java API for sending and receiving emails via SMTP, POP3, and IMAP. It is implemented as an optional package compatible with any operating system. At the same time, Jakarta Mail is supplied as a part of Jakarta EE and Java EE platforms. In the earlier releases, the mail package was titled “JavaMail API”. However, since July 2019, the Java software has been further developed by the Eclipse Foundation. This is why the email package also got the new name. All main classes and properties are the same for both JavaMail and Jakarta Mail.
In this article, we will describe the main email package properties and will show how to send different types of messages.
Getting Started with Jakarta Mail (JavaMail)
To start working with Jakarta Mail, first of all, you should insert jakarta.mail.jar file into your CLASSPATH environment. You can download it from the (Jakarta Mail project page on GitHub)[https://javaee.github.io/javamail/].
Besides, you can find Jakarta Mail jar files in the Maven repository and add them to your environment with Maven dependencies:
Let’s focus on the main steps for preparing HTML email and sending it via an external SMTP server.
Jakarta Mail Classes and Syntax
Before we move to code, let’s review core classes and properties, which are most frequently used for building and sending messages with Jakarta Mail.
Session Class (javax.mail.Session) is the primary one connecting all the properties and defaults. The following methods are used to get the session object:
getDefaultInstance() returns the default session
public static Session getDefaultInstance/(Properties props)
public static Session getDefaultInstance(Properties props, Authenticator auth)
getInstance() returns the new session.
public static Session getInstance(Properties props)
public static Session getInstance(Properties props, Authenticator auth)
Message class (javax.mail.Message) is an abstract class for actually building an email message. We will mostly use its Mime Message (javax.mail.internet.MimeMessage) subclass and its main methods:
setFrom(Address[] addresses) sets the “From” header field.
public void addFrom(Address[] addresses)
addRecipients(Message.RecipientType type, String addresses) adds the given address to the recipient type.
public void addRecipient(Message.RecipientType type, Address[] addresses)
Message.RecipientType.TO “To”
Message.RecipientType.CC “Cc”
Message.RecipientType.BCC “Bcc”
MimeMessage.RecipientType.NEWSGROUPS “Newsgroups”
setSubject(String subject) sets the subject header field.
public void setSubject(String subject)
setText(String textmessage) sets the text as the message content using text/plain MIME type.
public void setText(String textmessage)
setContent(Object o, String type) sets this message’s content.
public void setContent(Object o, String type)
To send emails via an external SMTP server, use com.sun.mail.smtp package: it is an SMTP protocol provider for the JavaMail API that provides access to an SMTP server.
The main properties are:
mail.smtp.user, default username for SMTP.
mail.smtp.host, the SMTP server to connect to.
mail.smtp.port, the SMTP server port to connect to, if the connect() method doesn’t explicitly specify one. Defaults to 25.
To enable SMTP authentication, set the mail.smtp.auth property or provide the SMTP Transport with a username and password when connecting to the SMTP server.
We will show how to implement it later, when demonstrating code examples.
SMTPMessage class is a specialization of the MimeMessage class for specifying SMTP options and parameters. Simply use this class instead of MimeMessage and set SMTP options using the methods on this class.
public SMTPMessage(Session session)
Transport ( javax.mail.Transport) is an abstract class for sending messages.
Let’s now review how to implement classes and methods described above and write some Java code to send an email via an external SMTP server.
First of all, we need to define who sends what to who. So, use the SendEmail public class and set “from” and “to” email addresses and add the subject. With javax.mail.PasswordAuthentication class we will be able to require password authentication to send a message via SMTP server.
In the properties method, we will add the necessary SMTP settings and then create a mail Session object. Afterward, you can create a Message using the MimeMessage.
Finally, send your message with the Transport object.
Don’t forget to add Exceptions. This class enables you to get details on possible errors along with an understanding of how to debug them. The main one is MessagingException. It can be used within javax.mail, javax.mail.internet, and javax.mail.search packages. For example, AddressException for javax.mail.internet will be thrown if you offered a wrongly formatted address.
We will return to debugging a bit later in this post.
How to test emails in Java?
For testing email sending from Java, we will use Mailtrap, an online tool, which helps test, review, and analyze emails sent from dev, QA, or staging environments, without the risk of spamming your customers or colleagues. Once you have tested and verified that everything works properly, change settings for the server you use in production.
Input:
package com.example.smtp;
import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.Properties;
public class SendEmail {
public static void main(String[] args) {
// Put recipient’s address
String to = "test@example.com";
// Put sender’s address
String from = "from@example.com";
final String username = "1a2b3c4d5e6f7g";//username generated by Mailtrap
final String password = "1a2b3c4d5e6f7g";//password generated by Mailtrap
// Paste host address from the SMTP settings tab in your Mailtrap Inbox
String host = "smtp.mailtrap.io";
Properties props = new Properties();
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");//it’s optional in Mailtrap
props.put("mail.smtp.host", host);
props.put("mail.smtp.port", "2525");// use one of the options in the SMTP settings tab in your Mailtrap Inbox
// Get the Session object.
Session session = Session.getInstance(props,
new javax.mail.Authenticator() {
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(username, password);
}
});
try {
// Create a default MimeMessage object.
Message message = new MimeMessage(session);
// Set From: header field
message.setFrom(new InternetAddress(from));
// Set To: header field
message.setRecipients(Message.RecipientType.TO,
InternetAddress.parse(to));
// Set Subject: header field
message.setSubject("My first message with JavaMail");
// Put the content of your message
message.setText("Hi there, this is my first message sent with JavaMail");
// Send message
Transport.send(message);
System.out.println("Sent message successfully....");
} catch (MessagingException e) {
throw new RuntimeException(e);
}
}
}
Output:
Sending HTML Email
To send an HTML email, you should perform the same steps as for sending a simple text message, with only SendHTMLEmail class instead of just SendEmail. Also, you need to set content to the MimeMessage.setContent(Object, String) and indicate text/html type.
Input:
package com.example.smtp;
import javax.mail.*;
import javax.mail.internet.InternetAddress;
import javax.mail.internet.MimeMessage;
import java.util.Properties;
public class SendHTMLEmail {
public static void main(String[] args) {
String to = "johndoe@gmail.com";
String from = "yourmail@example.com";
final String username = "1a2b3c4d5e6f7g";//generated by Mailtrap
final String password = "1a2b3c4d5e6f7g";//generated by Mailtrap
String host = "smtp.mailtrap.io";
Properties props = new Properties();
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
props.put("mail.smtp.host", host);
props.put("mail.smtp.port", "2525");
// Get the Session object.
Session session = Session.getInstance(props,
new javax.mail.Authenticator() {
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(username, password);
}
});
try {
// Create a default MimeMessage object.
Message message = new MimeMessage(session);
message.setFrom(new InternetAddress(from));
message.setRecipients(Message.RecipientType.TO,
InternetAddress.parse(to));
message.setSubject("My HTML message");
// Put your HTML content using HTML markup
message.setContent(
"<div><span style=\"color:#57aaca;\">c</span><span style=\"color:#57aec5;\">o</span><span style=\"color:#57b2c0;\">l</span><span style=\"color:#57b6ba;\">o</span><span style=\"color:#57bbb5;\">r</span><span style=\"color:#56bfb0;\">f</span><span style=\"color:#56c3ab;\">u</span><span style=\"color:#56c7a5;\">l</span><span style=\"color:#56cba0;\"> </span><span style=\"color:#5ec3ab;\">m</span><span style=\"color:#65bbb6;\">e</span><span style=\"color:#6db3c1;\">s</span><span style=\"color:#75accd;\">s</span><span style=\"color:#7da4d8;\">a</span><span style=\"color:#849ce3;\">g</span><span style=\"color:#8c94ee;\">e</span></div>", "text/html");
// Send message
Transport.send(message);
System.out.println("Sent message successfully....");
} catch (MessagingException e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
}
Output:
In Mailtrap, you can also check the raw data of your message as well as its HTML source on separate tabs.
If you would like your message to contain both HTML and plain text, you need to build it using a MimeMultipart(“alternative”) object. You should create two different parts manually and insert them separately: text/plain body part as the first part in the multipart the text/html body part as the second one.
HTML Email with Images in Java
To add an image to your HTML email in Jakarta Mail, you can choose any of three regular options: CID, base64 image, or linked image.
To embed a CID image, you need to create a MIME multipart/related message:
Multipart multipart = new MimeMultipart("related");
MimeBodyPart htmlPart = new MimeBodyPart();
//add reference to your image to the HTML body <img src="cid:some-image-cid" alt="img" />
htmlPart.setText(messageBody, "utf-8", "html");
multipart.addBodyPart(htmlPart);
MimeBodyPart imgPart = new MimeBodyPart();
// imageFile is the file containing the image
imgPart.attachFile(imageFile);
// or, if the image is in a byte array in memory, use
// imgPart.setDataHandler(new DataHandler(
// new ByteArrayDataSource(bytes, "image/whatever")));
imgPart.setContentID("<some-image-cid>");
multipart.addBodyPart(imgPart);
message.setContent(multipart);
For a base64, or inlined image, include the encoded image data in the HTML body:
But remember that each Base64 digit represents 6 bits of data, so your actual image code will be pretty long. Besides, it affects the overall size of the HTML message, so it’s better not to inline large images.
The simplest way to add an image is just linking to the image hosted on some external server. Refer to your image as a link in the HTML body with an “img” tag:
To attach any type of files to your message, you need to build a MIME multipart message and indicate the attachFile method in the MimeBodyPart.
public void attachFile(File file, Multipart multipart, MimeBodyPart messageBodyPart) {
DataSource source = new FileDataSource(file);
messageBodyPart.setDataHandler(new DataHandler(source));
messageBodyPart.setFileName(file.getName());
multipart.addBodyPart(messageBodyPart);
}
Debug Jakarta Mail
Debugging plays a critical role in testing of email sending. In Jakarta Mail it’s pretty straightforward. Set debug to true in the properties of your email code:
props.put("mail.debug", "true");
As a result, you will get a step by step description of how your code is executed. If any problem with sending your message appears, you will instantly understand what happened and at which stage.
Here is how our HTML message debug output looks:
DEBUG: Jakarta Mail version 1.6.4
DEBUG: successfully loaded resource: /META-INF/javamail.default.address.map
DEBUG: getProvider() returning javax.mail.Provider[TRANSPORT,smtp,com.sun.mail.smtp.SMTPTransport,Oracle]
DEBUG SMTP: need username and password for authentication
DEBUG SMTP: protocolConnect returning false, host=smtp.mailtrap.io, user=diana, password=<null>
DEBUG SMTP: useEhlo true, useAuth true
DEBUG SMTP: trying to connect to host "smtp.mailtrap.io", port 2525, isSSL false
220 mailtrap.io ESMTP ready
DEBUG SMTP: connected to host "smtp.mailtrap.io", port: 2525
EHLO DESKTOP-NLP1GG8
250-mailtrap.io
250-SIZE 5242880
250-PIPELINING
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250-AUTH PLAIN LOGIN CRAM-MD5
250 STARTTLS
DEBUG SMTP: Found extension "SIZE", arg "5242880"
DEBUG SMTP: Found extension "PIPELINING", arg ""
DEBUG SMTP: Found extension "ENHANCEDSTATUSCODES", arg ""
DEBUG SMTP: Found extension "8BITMIME", arg ""
DEBUG SMTP: Found extension "DSN", arg ""
DEBUG SMTP: Found extension "AUTH", arg "PLAIN LOGIN CRAM-MD5"
DEBUG SMTP: Found extension "STARTTLS", arg ""
STARTTLS
220 2.0.0 Start TLS
EHLO DESKTOP-NLP1GG8
250-mailtrap.io
250-SIZE 5242880
250-PIPELINING
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250 AUTH PLAIN LOGIN CRAM-MD5
DEBUG SMTP: Found extension "SIZE", arg "5242880"
DEBUG SMTP: Found extension "PIPELINING", arg ""
DEBUG SMTP: Found extension "ENHANCEDSTATUSCODES", arg ""
DEBUG SMTP: Found extension "8BITMIME", arg ""
DEBUG SMTP: Found extension "DSN", arg ""
DEBUG SMTP: Found extension "AUTH", arg "PLAIN LOGIN CRAM-MD5"
DEBUG SMTP: protocolConnect login, host=smtp.mailtrap.io, user=1e2b3c4d5e6f7g, password=<non-null>
DEBUG SMTP: Attempt to authenticate using mechanisms: LOGIN PLAIN DIGEST-MD5 NTLM XOAUTH2
DEBUG SMTP: Using mechanism LOGIN
DEBUG SMTP: AUTH LOGIN command trace suppressed
DEBUG SMTP: AUTH LOGIN succeeded
DEBUG SMTP: use8bit false
MAIL FROM:<yourmail@example.com>
250 2.1.0 Ok
RCPT TO:<johndoe@gmail.com>
250 2.1.0 Ok
DEBUG SMTP: Verified Addresses
DEBUG SMTP: johndoe@gmail.com
DATA
354 Go ahead
Date: Tue, 30 Jul 2019 17:19:31 +0200 (EET)
From: yourmail@example.com
To: johndoe@gmail.com
Message-ID: <20132171.0.1548256771226@DESKTOP-NLP1GG8>
Subject: My HTML message
MIME-Version: 1.0
Content-Type: text/html; charset=us-ascii
Content-Transfer-Encoding: 7bit
<div><span style="color:#57aaca;">c</span><span style="color:#57aec5;">o</span><span style="color:#57b2c0;">l</span><span style="color:#57b6ba;">o</span><span style="color:#57bbb5;">r</span><span style="color:#56bfb0;">f</span><span style="color:#56c3ab;">u</span><span style="color:#56c7a5;">l</span><span style="color:#56cba0;"> </span><span style="color:#5ec3ab;">m</span><span style="color:#65bbb6;">e</span><span style="color:#6db3c1;">s</span><span style="color:#75accd;">s</span><span style="color:#7da4d8;">a</span><span style="color:#849ce3;">g</span><span style="color:#8c94ee;">e</span></div>
.
250 2.0.0 Ok: queued
DEBUG SMTP: message successfully delivered to mail server
QUIT
221 2.0.0 Bye
Sent message successfully....
Need More Options?
In this post, we have guided you through the main Jakarta Mail use cases and options. Should you experience any difficulties with installing, implementing, or using this package, refer to the Jakarta Mail FAQ.
Indeed, constructing transactional emails to send from your Java app with Jakarta Mail API takes time. Alternatively, you can consider options for simplified email sending in Java. For example, the Spring Framework or Apache Common Emails are quite popular, while the Play Framework offers a plugin for sending emails. Simple Java Mail is one of the simplest libraries ever – in fact, it is a wrapper around JavaMail API.
The following code snippet shows you how to remove time information from the java.util.Date object. The static method removeTime() in the code snippet below will take a Date object as parameter and will return a new Date object where the hour, minute, second and millisecond information have been reset to zero. To do this we use the java.util.Calendar. To remove time information we setting the calendar fields of Calendar.HOUR_OF_DAY, Calendar.MINUTE, Calendar.SECOND and Calendar.MILLISECOND to zero.
You have type a long line of command in terminal. But now you want to clear or delete the entire line. Deleting each character in the command will take sometime and bored you. So are there any keyboard shortcuts that allow you to do this? Yes there are some hotkeys to the rescue.
Hotkeys
Description
CTRL + u
Delete the current command. The deleted command will be stored into a buffer.
CTRL + w
Delete a word.
CTRL + c
Abort what you are typing.
CTRL + d
Delete current character.
Other hotkeys that might help you work faster in the terminal.
The following code snippet demonstrates how to use RandomStringGenerator class from the Apache Commons Text library to generate random strings. To create an instance of the generator we can use the RandomStringGenerator.Builder() class build() method. The builder class also helps us to configure the properties of the generator. Before calling the build() method we can set the properties of the builder using the following methods:
withinRange() to specifies the minimum and maximum code points allowed in the generated string.
filteredBy() to limits the characters in the generated string to those that match at least one of the predicates supplied. Some enum for the predicates: CharacterPredicates.DIGITS, CharacterPredicates.LETTERS.
selectFrom() to limits the characters in the generated string to those who match at supplied list of Character.
usingRandom() to overrides the default source of randomness.
After configuring and building the generator based the properties defined, we can generate the random strings using the generate() methods of the RandomStringGenerator. There are two methods available:
generate(int length) generates a random string, containing the specified number of code points.
generate(int minLengthInclusive, int maxLengthInclusive) generates a random string, containing between the minimum (inclusive) and the maximum (inclusive) number of code points.
And here is your code snippet:
package org.kodejava.example.commons.text;
import org.apache.commons.text.CharacterPredicates;
import org.apache.commons.text.RandomStringGenerator;
public class RandomStringDemo {
public static void main(String[] args) {
RandomStringGenerator generator = new RandomStringGenerator.Builder()
.withinRange('0', 'z')
.filteredBy(CharacterPredicates.DIGITS, CharacterPredicates.LETTERS)
.build();
for (int i = 0; i < 10; i++) {
System.out.println(generator.generate(10, 20));
}
}
}
Below are examples of generated random alphanumeric strings:
The ArrayIndexOutOfBoundsException exception is thrown to indicate that an array has been accessed with an illegal index. The index is either negative or greater than or equal to the size of the array.
For example see the code snippet below:
String[] vowels = new String[]{"a", "i", "u", "e", "o"}
String vowel = vowels[10]; // throws the ArrayIndexOutOfBoundsException
Above we create a vowels array with five elements. This will make the array have indexes between 0..4. On the next line we tried to access the tenth element of the array which is illegal. This statement will cause the ArrayIndexOutOfBoundsException thrown.
We must understand that arrays in Java are zero indexed. The first element of the array will be at index 0 and the last element will be at index array-size - 1. So be careful with your array indexes when accessing array elements. For example if you have an array with 5 elements this mean that the index of the array is from 0 to 4.
If you are trying to iterate an array using for loop. Make sure the index start from 0 and execute the loop while the index is less than the length of the array, you can get the length of the array using the array length property. Let’s see the code snippet below:
for (int i = 0; i < vowels.length; i++) {
String vowel = vowels[i];
System.out.println("vowel = " + vowel);
}
Or if you don’t need the index you can simplify your code using the for-each or enhanced for-loop statement instead of the classic for loop statement as shown below:
There are times when you need to create a user only to have a read-only access to a database. The user can view or read the data in the database but they cannot make any changes to the data or the database structure.
Creating a New User Account
To create a read-only database user account for MySQL do the following steps:
First, login as a MySQL administrator from your terminal / command prompt using the following command:
mysql -u root -p
You’ll prompted to enter the password. Type the password for the root account.
Create a new MySQL user account.
CREATE USER 'report'@'%' IDENTIFIED BY 'secret';
The % in the command above means that user report can be used to connect from any host. You can limit the access by defining the host from where the user can connect. Omitting this information will only allow the user to connect from the same machine.
Grant the SELECT privilege to user.
GRANT SELECT ON kodejava.* TO 'report'@'%';
Execute the following command to make the privilege changes saved and take effect.
FLUSH PRIVILEGES;
Type quit to exit from the MySQL shell.
Test the New User Account
Now we can try the newly created user account. Start by login with the new user account and provide the corresponding password.
mysql -u report -p
Try executing the DELETE command:
mysql> USE kodejava;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
Database changed
mysql> DELETE FROM authors;
ERROR 1142 (42000): DELETE command denied to user 'report'@'localhost' for table 'authors'
mysql> UPDATE authors SET name = 'Wayan Saryada' WHERE id = 1;
ERROR 1142 (42000): UPDATE command denied to user 'report'@'localhost' for table 'authors'
mysql>
