Articles
Advanced Java

java observer mode

In message queues such as activeMQ, we often use the publish-subscribe model, but have you ever thought about how to get the information of the subscribed topic in time on the client? In fact, the observer mode is used here. In a software system, the observer pattern is quite useful when the behavior of one object depends on the state of another object. If we do not use the general structure provided by the observer mode, but we need to implement similar functions, think about how we can achiev

... Cole
schedule 7 min read
Advanced Java

Extract the consistent hash code of the jedis source code as a general tool class

Consistent Hash hotspotThe consistent Hash algorithm is to solve the hotspot problem. If the virtual node is set too small, the hotspot problem still exists. I won’t talk about the principle of the consistent Hash algorithm. Many people on the Internet provide code examples of the consistent Hash algorithm written by themselves. I found that there are still hot issues in the code examples on the Internet. For this reason, I read the source code of Jedis's ShardedJedis class and extracted its con

... Mackenzie
schedule 6 min read
Advanced Java

Thread interruption of jdk1.8

There is a saying in Core Java: "There is no language requirement that an interrupted program should be terminated. Interrupting a thread is only to attract the attention of the thread, and the interrupted thread can decide how to respond to the interruption." Thread interruption will not cause The thread exits immediately, but instead sends a notification to the thread to inform the target thread that someone wants you to exit. As for how the target thread handles after receiving the notificati

... Melody
schedule 5 min read
Advanced Java

Use of Linux shell programming functions

The linux shell can user-defined functions, and then can be called casually in the shell script. Let's talk about its definition method, and those things that need to be paid attention to when calling. Function definition#!/bin/sh # func1.sh hello() ## Function definition { echo "Hello there today's date is `date +%Y-%m-%d`" # return 2 ###The return value is actually a status code, which can only be in the range of [0-255] } hello #function call echo $? #Getting the return value of the function

... Jayla
schedule 4 min read
Advanced Java

Linux shell programming condition judgment-if, while, for, case

if syntax formatif condition then statements [elif condition then statements] [else statements] fiExamplevi if.sh#!/bin/bash if [$1 = root] then echo "hello $2, welcome !" elif [$1 = intsmaze] then echo "hello ${2}, welcome !" else echo "SB${2}, get out here !" fish if.sh intsmaze nihao When executing the script, pass in the parameters after the script command.Analyzing conditions1: Basic grammar of conditional judgment[condition]  (note that there must be spaces before and after the condit

... Jude
schedule 4 min read
Advanced Java

hbase1.1.4 cluster construction

hbase1.1.4 cluster constructionFirst deploy a zookeeper cluster and hadoop cluster.(1) Upload the hbase installation package to the intsmaze01 node(2) Unzip(3) To configure the hbase cluster, 3 files need to be modified Note: Put the hdfs-site.xml and core-site.xml of hadoop under hbase/conf(3.1) Modify hbase-env.shexport JAVA_HOME=/usr/java/jdk1.7.0_55 //Tell hbase to use external zk export HBASE_MANAGES_ZK=false(3.2) Modify hbase-site.xml<configuration> <!-- Specify the path where hba

... Angel
schedule 2 min read
Core Java

Talk about cache update

I have seen that when many people write code to update cached data, they delete the cache first, and then update the database , and subsequent operations will load the data into the cache again. However, this is logically wrong . Imagine two concurrent operations, one is an update operation and the other is a query operation. After the update operation deletes the cache, the query operation does not hit the cache. The old data is first read out and then placed in the cache, and then the update o

... Steven
schedule 9 min read
Core Java

SpringAOP those ubiquitous dynamic proxies

Environment configurationCode structurepom.xml file xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> 4.0.0 com.gupaoedu gupaoedu-springaop 0.0.1-SNAPSHOT gupaoedu-springaop 1.8 org.projectlombok lombok 1.16.10 org.slf4j slf4j-api 1.7.25 ch.qos.logback logback-classic 1.2.3 application.properties file #Multi-faceted configuration can be prefixed in front of the key #For example aspect.logAspect. #Section expression,expression# pointCut=public.

... Isaiah
schedule 6 min read
Core Java

Those high-quality tools that can help you increase your development efficiency tenfold

There are many tools in the Java world, from well-known IDEs (such as Eclipse, NetBeans and IntelliJ IDEA) to JVM profiling and monitoring tools (such as JConsole, VisualVM, Eclipse Memory Analyzer, etc.).In this article, I will focus on general tools for various Java developers (such as core Java and web developers). This list is by no means a complete list of tools. If you know some good tools that developers should learn, please share with you in the comments section.1. GitFor Java programmer

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

SQL optimization LIMIT syntax, what is the difference between limit n, m and limit n?

In some interview questions, you will encounter such question and answer or written test: "What is the difference between limit 0,1 and limit 1?" To answer this question accurately, you need to understand the essential difference between one parameter and two parameters. The first parameter n in limit n, m indicates the offset of the cursor, the initial value is 0, and the second parameter m indicates how many pieces of data you want to get. So limit 0,1 means that starting from the first recor

... Nathan
schedule 4 min read
Java Back End Development

Java concurrent programming thread safety and performance

The thread safety performance of the class is: atomicity of operation, similar to database transactions. The visibility of the memory can be seen immediately by other threads after the current thread is modified. Without proper synchronization, thread insecurity will occur when state is shared between multiple threads. There are three security strategies as follows: 1. Stack closure Stack closure means that variables are declared inside the method, and these variables are in the stack closure st

... Brandon
schedule 8 min read
Java Back End Development

In-depth interpretation of Redis development specifications, don't just set and get!

Key naming design: readability, manageability, brief introduction The specification recommends the use of colons, namely: segmentation and splicing, because many Redis clients are classified according to colons, as shown in the following figure:Value design: reject large-capacity keys The specification recommends that the value of the String type be controlled within 10KB. This is because Redis continues to grow as the value exceeds 10KB, and a very strange performance inflection point will occ

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

New Features of Java 1.8-Srream Stream

The Java 8 API adds a new abstraction called Stream, which allows you to process data in a declarative manner, allowing programmers to write efficient, clean, and concise code. This style regards the collection of elements to be processed as a kind of flow. The flow is transmitted in the pipeline and can be processed on the nodes of the pipeline, such as filtering, sorting, grouping, and so on.The element stream is processed by an intermediate operation in the pipeline, and finally the result o

... Adrian
schedule 9 min read
Java Back End Development

New Features of Java 1.8-Method Reference

Introduction: Method references refer to a method by the name of the method. Method reference can make the structure of the language more compact and concise, and reduce redundant code. Method references use a pair of colons (::), which are generally passed in as parameters and cannot be used alone.Method reference example 1:Use class static method references, ordinary object method references, constructor references:public static class Car { public static Car create( final Supplier< Car>

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

Java1.8-Lambda expression

Lambda expression Lambda expressions can also be called closures (note that they are not the same concept as closures in js). It allows functions to be used as parameters of a method (functions are passed into methods as parameters). Using Lambda expressions can make the code It becomes more concise and compact.grammar:(parameters) -> {expression;} or: (parameters) -> expression or: parameters -> {expression;} or: parameters -> expression;Important features of lambda expressions:Opti

... Kaden
schedule 3 min read
Java Web Development

java.sql.SQLException: Value '0000-00-00 00:00:00' can not be represented as java.sql.Timestamp

The error message is as follows:java.sql.SQLException: Value '0000-00-00 00:00:00' can not be represented as java.sql.Timestamp at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:963) ~[mysql-connector-java-5.1.39.jar:5.1.39] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896) ~[mysql-connector-java-5.1.39.jar:5.1.39] at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885) ~[mysql-connector-java-5.1.39.jar:5.1.39] at com.mysql.jdbc.SQLError.createSQLException(SQLEr

... Adrian
schedule 2 min read
Java Web Development

springboot2.0 war starts under tomcat and keeps 404

Modify the pom file<build> <finalName>springboot2.0</finalName> <!--<pluginManagement>--><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) --> <plugins> <plugin> <artifactId>maven-clean-plugin</artifactId> <version>3.1.0</version> </plugin> <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging --> <plugin> &lt

... Bradley
schedule 1 min read
Java Web Development

There is no main list exception when springboot 2.0 hits the jar. Springboot hits the jar package and first adds the dependent jar package to run and reports that there is no main list exception.

Springboot hits the jar package and adds the dependency first <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.8</source> <target>1.8</target> </configuration> </plugin> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <mainClass>com.Star

... Olivia
schedule 1 min read
Java Web Development

Springboot2.0+yml integrates multiple data sources. The configuration file is as follows. Read the configuration file.

The configuration file is as followsspring: datasource: test1: name it yourself driver-class-name: com.mysql.jdbc.Driver username: root password: root url: jdbc:mysql://localhost:3306/test?characterEncoding=UTF-8 test2: name it yourself driver-class-name: com.mysql.jdbc.Driver username: root password: root url: jdbc:mysql://localhost:3306/springboot?characterEncoding=UTF-8Read configuration file Read the first data source codepackage com.datasource; import org.apache.ibatis.session.SqlSessionFac

... Bryce
schedule 6 min read
Java Web Development

springboot2.0 multi-data source integration problem At least one JPA metamodel must be present! at Data source code: startup error message: reason does not specify the main data source

Data source code: The first code to read the configuration file:package com.datasource; import org.apache.ibatis.session.SqlSessionFactory; import org.mybatis.spring.SqlSessionFactoryBean; import org.mybatis.spring.SqlSessionTemplate; import org.mybatis.spring.annotation.MapperScan; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.boot.context.properties.ConfigurationProperties; import org.springframework.boot.jdbc.DataSourceBuilder; import org.springfram

... Brady
schedule 4 min read
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