Articles
Advanced Java

javaOOM should analyze the dump file instead of looking at the abnormal log.

The application has an OOM exception, do you still troubleshoot the problem by looking at the log (it is only a coincidence that this method is used to locate and solve the problem)? The correct troubleshooting plan is to analyze the dump file. Do you know why?OOM exception--intsmazeFirst of all, the OOM exceptions I encountered during development are basically located by looking at the log log (many OOM exceptions are caused by an infinite loop or the amount of data returned by the query, no pa

... Sophia
schedule 6 min read
Advanced Java

How to traverse hundreds of millions of files in a folder without stack overflow

Preface: There are many layers of small files under a folder. How to calculate how many files are under this folder? Recursive traversal, simple violence, recursion is indeed a more convenient solution in general, but when the depth of the folder is deep, repeated recursive calls will cause the method to never be released, causing the jvm stack overflow. What should we do? To be honest, I have never encountered this problem before. I heard from an IT senior I admire about his previous interview

... Isaiah
schedule 4 min read
Advanced Java

Banking--The influence of weather on consumer behavior--geographical location marketing model

As a technical consultant in the consulting industry, he serves various banks and other financial institutions, and launches solutions suitable for users based on their business characteristics. This plan is a tailor-made marketing plan for a bank in the last month, but it was finally cut off due to data problems. From this I thought, Jack Ma’s father said that big data is the new oil is correct, but my interpretation is that it is not that the more data the better, but the more diversity of da

... Patrick
schedule 9 min read
Advanced Java

JMX, Jstatd are the last layer of guarantee for the launch of JVM applications

A successful java project standard is not only about the realization of business functions, but looking at the country, many project teams only consider business functions in the development and design of the preliminary project, and do not consider the monitoring design for later maintenance of the project. Without a complete monitoring operation and maintenance design, the project's survival life should not be long, right? Good projects can attract people to stay, and constantly strengthen the

... Isabel
schedule 11 min read
Advanced Java

3.sparkSQL integrates Hive

Spark SQL often needs to access Hive metastore. Spark SQL can obtain Hive table metadata through Hive metastore . Starting from Spark 1.4.0, Spark SQL only needs a simple configuration to support access to all versions of Hive metastore. Note that Spar SQL ignores the Hive version when it comes to metastore. Spark SQL internally decompiles Hive to Hive 1.2.1. Spark SQL's internal operations (serdes, UDFs, UDAFs, etc) all call Hive 1.2.1 classes. Spark SQL and hive share a set of metadata Spark S

... Abraham
schedule 6 min read
Advanced Java

IT consultant: fire fighting project triggered by group by and join

I fired the project again. This time the reason was that the entire business system review process caused serious errors due to group by and join indiscriminately. The basic SQL table association, group by, and sub-tables are unclear. Very simple one-to-many table associationIn the user table, customerId represents the unique id of the user, and insertTime represents when this piece of data is stored. Corresponding to the form table, the foreign key customerId indicates which customer the p

... Bentley
schedule 5 min read
Core Java

One literature meeting JVM performance optimization

Actual combat performance optimizationRecognize JVMBefore we drew a picture of the process from the Class file to the class loader, and then to the runtime data area. Now let's enrich and perfect this picture to show the general physical structure of the JVM.Execution engine: used to execute JVM bytecode instructionsThere are two main ways to achieve it:(1) Translate the input bytecode instruction into another type of virtual machine instruction during loading or execution;(2) Translate the inpu

... Daisy
schedule 9 min read
Core Java

Explore the JVM, just this article!

1 official website 1.1 The process of looking for JDK documentationwww.oracle.com -> Product Documentation in the lower right corner -> drop down to select Java -> Java SE documentation-> Previous releases -> JDK 8 -> Now locate: https://docs.oracle.com/javas.. .1.2 The relation of JDK/JRE/JVMReference -> Developer Guides -> Locate: https://docs.oracle.com/javas... Oracle has two products that implement Java Platform Standard Edition (Java SE) 8: Java SE Development Kit (

... Carter
schedule 21 min read
Core Java

Spring high-frequency interview questions, what can you answer? (Advanced)

1. What is the Spring framework? What are the main modules of the Spring framework?2. What are the benefits of using the Spring framework?3. What is Inversion of Control (IOC)? What is dependency injection?4. Please explain the IoC in the Spring framework?5. What is the difference between BeanFactory and ApplicationContext?6. How many configuration methods does Spring have?7. How to configure Spring based on XML configuration?8. How to configure Spring based on Java configuration?9. How to confi

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

Algorithm and Programming-IO Stream

Write a program to alternately merge the words in the a.txt file and the words in the b.txt file into the c.txt file, the words in the a.txt file are separated by carriage returns, and the carriage return in the b.txt file Or separated by spaces. If you encounter this question in an interview, don't panic, because the original intention of the questioner may not be to write this program right away, but to consider your thinking ability. In fact, it is difficult to write this code in a short per

... Mackenzie
schedule 6 min read
Java Back End Development

Programming thoughts-troublesome paging, to remove duplicate problems

Recently, I encountered a troublesome problem. When developing the audit function, you need to query the audited records. It must be a single corresponding to multiple audit records, so multiple audit records are displayed. Suddenly the product needs to remove the excess. A single sheet only displays the most recent audit records. I removed the excess in a loop at the beginning. After removing it, I found an embarrassing problem, that is, the front-end pagination display: 10 items per page, tot

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

Idea automatically generates classes and method annotations, greatly improving development efficiency

In the development process, we need to write comments for new classes, methods, interfaces, etc. It is a waste of time to write comments frequently. Below I will introduce a way to automatically generate comments.Operating procedures1. Open Settings1. Open Eduitor1. Select File and Code Templates1. Select Files1. Select Class2. Select Interface3. Select Enum and so on... Including comments can also be set.One: Generate class annotations #if (${PACKAGE_NAME} && ${PACKAGE_NAME} != "")pack

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

Fun with mysql correspondence: concat and group_concat

The examples used in this article are all executed under the following database table tt2:One, concat() function1. Function: Concatenate multiple strings into one string.2. Syntax: concat(str1, str2,...)The return result is the string generated by the connection parameter. If any parameter is null, the return value is null.3. Examples:Example 1: select concat (id, name, score) as info from tt2;There is a null row in the middle because there is a row in the tt2 table whose score value is null.Exa

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

The topmost object Object in javaScript

JavaScript follows the rules of Java and also designs a top-level "parent" object Object. All objects inherit Object by default, and all objects can be regarded as instances of Object. According to the inheritance rules, the subclass has the methods and properties of the parent class, so all objects in javaScript have many methods and properties by default, such as toString. Of course, we can also customize methods on Object, so all objects will have this method Object.prototype.print = function

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

JavaScript core technology-"closure", I absolutely regret not looking at it!

"Closing", also known as "functions defined in functions", closure technology is a key core technology in javaScript, and many framework development or high-end enterprise technologies need to use it. To understand the closure technique, you must first understand the "scope of variables". 1. The scope of the variable javaScript followed the variable rules of java, but slightly improved. Like java, it can be divided into "global variables" and "local variables". The "local variables" in javaScri

... Sophia
schedule 8 min read
Java Web Development

springboot2.0 常见问题找不到

The error message is as follows . ____ _ __ _ _ /\/___'_ __ _ _(_)_ __ __ _///\ ( ( )\___ | '_ | '_| | '_//_` |///\ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, |//// =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.0.1.RELEASE) 2019-05-17 11:59:15.026 INFO 7792 --- [ main] com.bdqn.Start : Starting Start on PC-20180826RQMV with PID 7792 (E:\IDEA\springboot1\target\classes started by Administrator in E:\IDEA\springboot1) 2019-05-17 11:59:15.031 INFO 7792 ---

... Aubrey
schedule 5 min read
Java Web Development

springcloud reported an error Load balancer does not have available server for client:XXXX

Call with feign interfaceThe error message is as follows com.netflix.client.ClientException: Load balancer does not have available server for client: app-member at com.netflix.loadbalancer.LoadBalancerContext.getServerFromLoadBalancer(LoadBalancerContext.java:483) ~[ribbon-loadbalancer-2.2.4.jar:2.2.4] at com.netflix.loadbalancer.reactive.LoadBalancerCommand$1.call(LoadBalancerCommand.java:184) ~[ribbon-loadbalancer-2.2.4.jar:2.2.4] at com.netflix.loadbalancer.reactive.LoadBalancerCommand$1.call

... Dominic
schedule 2 min read
Java Web Development

Springcloud-feign call

EurekaConfiguration file###Service start port number server: port: 8100 ###Service name (service registered to eureka name) spring: application: name: app-itmayiedu-server ###Service registered to eureka address eureka: client: service-url: defaultZone: http://localhost:8100/eureka ###Because the application is a registration center, it will not register itself register-with-eureka: true ###Do you need to obtain registration information from eureka fetch-registry: trueStart class@EnableEurekaSer

... Levi
schedule 2 min read
Java Web Development

java import and parse excel content and store it in the database springboot+mybatis

maven depends on jar <!--Import the package needed for the form--> <dependency> <groupId>org.apache.poi</groupId> <artifactId>poi-ooxml</artifactId> <version>3.9</version> </dependency> <dependency> <groupId>commons-fileupload</groupId> <artifactId>commons-fileupload</artifactId> <version>1.3.1</version> </dependency> <dependency> <groupId>commons-io</groupId> <artifactId&gt

... Kaden
schedule 6 min read
Java Web Development

Let your IDEA be set once and used in multiple places

Introduction: IDEA is considered to be the best IDE for Java development. I believe that many friends have encountered the situation of repeatedly setting IDEA on multiple computers. Today, Mo Bai brings you a way to store IDEA settings in a remote warehouse and change the computer. Only need to pull to complete the setting method, which greatly simplifies your operation!One :Open your browser and go to the GitHub official website. If you don't have an account, register one yourself. If you have

... Leonardo
schedule 2 min read
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