Articles
Advanced Java

Linux Practice-Create User

Create an admin user for daily operations (root authority is too high to be used directly).Create new useradduser [username][root@VM_0_8_centos ~]# adduser adminset passwordpasswd [username]The system has certain requirements for the password, it can't be too simple, otherwise. . .[root@VM_0_8_centos ~]# passwd admin Change the password of the user admin. New password: Invalid password: the password did not pass the dictionary check-it does not contain enough different characters Re-enter the n

... Noah
schedule 5 min read
Advanced Java

Timing task practice in distributed scenarios

Background Applications often require some tasks to be executed regularly, which can be easily implemented through the @Scheduled annotation in spring.However, Goose’s current projects generally do not only deploy one instance, at least two units must be deployed to support uninterrupted service releases. It is not a big problem to deploy more than a dozen or dozens of units.In this way, when we write a timed task, we need to consider whether all instances of the task will be executed when the t

... Jayden
schedule 7 min read
Advanced Java

Speaking of TCP's three-way handshake and four waved hands

Transmission Control Protocol (TCP, Transmission Control Protocol) is a connection-oriented, reliable, byte stream-based transport layer communication protocol.The HTTP we are familiar with is based on TCP.TCP connection is also a very high-frequency topic in interviews. The general interviewer's starting method is: please talk about TCP's three-way handshake/four-time wave...The outline of this article is as follows, if you don’t finish it, you can collect it and watch it slowly.Simple explanat

... Eric
schedule 10 min read
Advanced Java

Interesting shift operations in JAVA

<<, >>, <<<, >>> What do these symbols mean? What are the details that are easily missed?Last time I introduced interesting bit operations in JAVA . I learned that bit operations are directly operating on a reshaped binary bit. The efficiency is much higher than addition, subtraction, multiplication and division, so it is often used in performance-sensitive scenarios.Today we will introduce the shift operation in binary.Original code, inverse code, complementSharpen

... Ezekiel
schedule 10 min read
Advanced Java

Interesting bit operations in JAVA

&, |, ^, ~ What do these symbols mean? What's the magical effect? Let's feel their magic together~When we look at some source code, we often see symbols such as &, |, ^, ~, these are bitwise operators.Bit arithmetic is to directly operate on a reshaped binary bit. The efficiency is much higher than that of addition, subtraction, multiplication and division, so it is often used in performance-sensitive scenarios.& And operationIn the binary format, each bit (1 or 0) of the two numbers

... Madison
schedule 5 min read
Advanced Java

Is String in JAVA really immutable?

Is String immutable? Yes it is! Really want to change? Ok~We all know that String is an immutable object, that is, once it is created, its state cannot be changed. In this regard, let's analyze a wave.Internal structure of StringCarefully enter the String inside, we can see that it is a final class, then no one can inherit it, very good, very dink.Then look directly at its soul, a char array, which is also final, so we know how it is immutable.public final class String implements java.io.Seriali

... Max
schedule 3 min read
Core Java

Ten reasons to learn microservices

Ten reasons to learn microservicesMicroservices are the future trend of software architects. Need persuasiveness? Check out the top ten reasons to understand this new architecture.Understand the advantages and principles of enterprise microservice architectureAlways pay attention to new technologies, languages ​​and frameworks to revolutionize your organization. If you are still messing with the code in the overall framework in your cube, then you may be living in the past where there was a smal

... Lucas
schedule 5 min read
Core Java

6. Choose a deployment strategy

This book mainly introduces how to use microservices to build applications. This is the sixth chapter of the book. The first chapter introduces the microservice architecture pattern and discusses the advantages and disadvantages of using microservices. The following chapters discuss all aspects of microservice architecture: use of API gateways , inter-process communication , service discovery, and event-driven data management . In this chapter, we will introduce strategies for deploying microser

... Landon
schedule 16 min read
Core Java

Hibernate print SQL and additional parameters

In the Hibernate configuration file hibernate.cfg.xml, there are 3 settings related to the display of SQL statements, and their values ​​are all boolean values: 1. show_sql: whether to display the SQL statement 2. format_sql: whether to format the output string, enhanced The readability of SQL 3. use_sql_comments: Whether to display comments, used to indicate what operation generated the SQL statement.If show_sql=true is set, only SQL statements will be printed by default without printing parame

... Braxton
schedule 1 min read
Java Back End Development

15 kinds of loop traversal of js, how many have you mastered?

Method 1: Native js loop 1.while loop: The While statement includes a loop condition and a block of code. As long as the condition is true, the code block will be executed continuously.grammar: while (condition) { Statement; } // or while (condition) statement; //for example:var i = 0; while (i <100) { console.log('i is currently:' + i); i = i + 1; }2. do……while loopThe do...while loop is similar to the while loop. The only difference is that the loop body is run once, and then the loop condi

... Austin
schedule 12 min read
Java Back End Development

Java generics

If we only write a sort method, we can sort integer arrays, string arrays, and even any type of array that supports sorting, which would be great.Java generic methods and generic classes allow programmers to use a method to specify a set of related methods, or use a class to specify a set of related types.Java generics (generics) is a new feature introduced in JDK 5. Generics provide a compile-time type safety detection mechanism, which allows programmers to detect illegal types at compile time

... Hannah
schedule 5 min read
Java Back End Development

AOP advanced usage-get method parameters and return values

When we usually use springAop, we often define a certain method as an entry point for pre, post or surround enhancement, but if we want to get the parameters of the entry point method and its return value, we need to do something Specific configuration.The general aspect is as follows:@Configuration @Aspect public class UserInfoAspect { @Pointcut("execution(* com.*.test(*))") public void test() {} @AfterReturning(value = "test()"") public void logMethodCall() throws Throwable { System.out.print

... Ashley
schedule 2 min read
Java Back End Development

Recursive algorithm: calculate the value of 1+2+3+……+n

public class Main { public static int test(int n){ int temp = 0; if (n-1>0){ temp = n + test(n-1); }else { temp = n; } return temp; } public static void main(String[] args) { int test = test(10); System.out.println(test); } }Test Results:55 To understand the algorithm, you need to understand recursion. Many people only know that recursion calls themselves, but they do not understand the relationship between the scope of their own variables. In fact, every time you call yourself, its variables

... Asher
schedule 2 min read
Java Back End Development

New feature of Java 1.8-interface default method

In the past, there were often interview questions asking whether specific methods could be written in the interface, but now there are still some rookies who will come up with this interview question. Java 8 adds the default method of the interface. Simply put, the default method is that the interface can have implementation methods, and no implementation class is required to implement its methods. We only need to add a default keyword in front of the method name to implement the default method.

... Henry
schedule 3 min read
Java Back End Development

New Features of Java 8-Functional Interface

JDK1.8 provides a special interface-Functional Interface. Compared with ordinary interfaces, it has one more method than ordinary interfaces. Functional interfaces can be implicitly converted to lambda expressions. The existing functions of the functional interface can support lambda friendly.In fact, there were some functional interfaces as early as JDK 1.8, as follows:java.lang.Runnablejava.util.concurrent.Callablejava.security.PrivilegedActionjava.util.Comparatorjava.io.FileFilterjava.nio.fi

... Harrison
schedule 6 min read
Java Web Development

Interview question: Distributed transaction

1.What is distributed?With the popularity of microservice architecture, a large-scale business system is often composed of several subsystems, and these subsystems have their own independent databases. Often a business process needs to be completed by multiple subsystems, and these operations may need to be completed in one transaction. In microservice systems, these business scenarios are ubiquitous. At this time, we need to implement cross-database transaction support through some means on th

... Dominic
schedule 4 min read
Java Web Development

Take you to learn the simplest paging plug-in PageHelper

Introduction:PageHelper is an excellent open source mybatis paging plugin in China. It supports basic mainstream and commonly used databases, such as mysql, oracle, mariaDB, DB2, SQLite, Hsqldb, etc. Today, Mo Bai will talk to you about the PageHelper paging plug-in. Below is the open source address of PageHelper. Interested friends can check it out.PageHelper's project address on github: https://github.com/pagehelper/Mybatis-PageHelperFirst introduce this plug-in PageHelperOfficial website addr

... Elijah
schedule 5 min read
Java Web Development

Explain Lambda expressions in detail

Introduction:An overview of the idea of ​​functional programming: In mathematics, a function is a set of calculation schemes with input and output, that is, "do something with something". Relatively speaking, object-oriented overemphasizes "things must be done in the form of objects", while functional thinking tries to ignore the complex syntax of object-oriented—emphasizing what to do, not what form to do. What to do, not how to do it, do we really want to create an anonymous inner class object

... Angelina
schedule 9 min read
Java Web Development

A total of 50 SQL exercises with answers (MySQL)

I've been really busy and super busy recently. You can change the data according to your query needs. If your SQL is 6 then of course it is best. If you are not particularly good, I suggest you understand these 50 Sql questions. After you finish, you will find that you have made a lot of progress! !! Come on 1. Student table student(s_id,s_name,s_birth,s_sex) - Student number, student name, date of birth, student gender 2. Course table course(c_id, c_name, t_id) - Course number, course name, te

... Ella
schedule 23 min read
Java Web Development

Introduction and use of generics in Java

! Today, I will mainly tell you about the use of generics in Java and what is generics? Please see the text belowGeneric overview We all know that collections (list, map...) in Java can store any object, as long as the objects are stored in the collection, then they will all be promoted to the Object type. When we take out each object and perform the corresponding operation, we must use type conversion. Look at the following sample codepackage com.mobaijun; import java.util.ArrayList; import jav

... Jackson
schedule 8 min read
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