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Use regular expressions to determine whether there are duplicate characters in a string

This article introduces how to use Java regular expressions to determine whether a fixed-length string contains duplicate characters. The core idea is to use reverse matching, that is, to find a string containing duplicate characters, and then determine whether the target string does not match the expression. The article will provide detailed regular expressions and provide Java code examples to help readers understand and apply the method.

Sep 08, 2025 am 04:48 AM

Retry strategy and implementation of deserialization exceptions in Kafka batch listener

This article details how to effectively handle and retry deserialization exceptions in Spring Kafka batch listener. By modifying the DefaultErrorHandler to cancel the fatal marking of DeserializationException, and combining the listener's internal exception information extraction and retweeting of messages with null payloads, retrying the entire batch of messages is achieved, thereby improving the robustness of Kafka applications.

Sep 08, 2025 am 04:27 AM

How to make a network connection in Java

TomakeanetworkconnectioninJava,useTCPsocketsforreliablecommunication:implementServerSocketontheserversidetolistenforconnectionsandSocketontheclientsidetoconnectandexchangedatausinginputandoutputstreams.2.Forconnectionlessandfastercommunication,useUDP

Sep 08, 2025 am 04:10 AM

How to define a record in Java

ArecordinJavaisaconcisewaytodefineimmutabledatacarriers,introducedinJava16;itautomaticallygeneratesconstructors,accessors,equals,hashCode,andtoStringmethods;1.DefineusingrecordTypeName(Typefield1,...);2.Fieldsareprivate,final,withpublicaccessormethod

Sep 08, 2025 am 03:55 AM

Implement custom endpoint authorization in Spring OAuth2 resource server

This article will guide you on how to implement custom token authorization for specific endpoints in Spring OAuth2 resource server. We will explore how to leverage JWT's private statement, Keycloak's Mapper functionality, and Spring Security's extension points (such as jwtAuthenticationConverter and custom AbstractAuthenticationTokens) to build a flexible and powerful authorization mechanism. In addition, it will also introduce how to authenticate trusted clients through Client Credentials Flow to achieve access control without user context.

Sep 08, 2025 am 03:51 AM

What are the ways to create a thread in Java?

ExtendingtheThreadclassinvolvescreatingaclassthatinheritsfromThreadandoverridestherun()method,thencallingstart()toexecuteitinanewthread,butthisapproachlimitsinheritancecapabilities.2.ImplementingtheRunnableinterfaceallowsaclasstodefinetasklogicinther

Sep 08, 2025 am 03:50 AM

java thread

How to read a file in Java

Forsmalltextfiles,useFiles.readAllLines()toreadalllinesintoalistatonce,whichissimplebutloadstheentirefileintomemory.2.Forlargetextfiles,useFiles.newBufferedReader()toreadlinebylineefficientlywithminimalmemoryusageandautomaticresourcemanagementviatry-

Sep 08, 2025 am 03:44 AM

java file reading

What is SQL injection and how can you prevent it in Java?

SQL injection vulnerabilities can be effectively prevented by using precompiled statements and parameterized queries because they ensure that user input is treated as data rather than executable code, thus preventing attackers from tampering with the SQL statement structure and ultimately eliminating the risk of SQL injection.

Sep 08, 2025 am 03:41 AM

How do you connect to a database in Java using JDBC?

ModernJDBCversionsautomaticallyloadthedriver,butolderversionsmayrequireClass.forName("com.mysql.cj.jdbc.Driver");2.EstablishaconnectionusingDriverManager.getConnection()withadatabaseURL,username,andpassword;3.CreateaStatementorPreparedState

Sep 08, 2025 am 02:01 AM

jdbc

$Use carriage return (\r) to overwrite the output in Java console$

Use carriage return (\r) to overwrite the output in Java console

This article aims to solve the problem that when Java programs use System.out.print("\r" message) to try to implement line overwrite updates in the console, the output becomes a line break. By analyzing the console settings of the Eclipse IDE, an effective solution is provided to help developers correctly use carriage return characters to achieve the expected output effect in a Windows environment.

Sep 08, 2025 am 01:51 AM

How to use multithreading in Java

TousemultithreadinginJava,extendtheThreadclassandoverridetherun()method,thencallstart()torunthreadsconcurrently.2.AbetterapproachisimplementingtheRunnableinterface,whichallowsclassinheritanceflexibilityandpromotescomposition.3.UseCallableandFuturewhe

Sep 08, 2025 am 01:44 AM

What is the java.time package in Java?

Thejava.timepackageinJavaprovidesareliableandintuitiveframeworkfordateandtimehandling,replacingtheflawedlegacyclasses.1.ItisbuiltonISO-8601andoffersimmutable,thread-safeclasses.2.KeyclassesincludeLocalDateTimefordate-timewithouttimezones,ZonedDateTim

Sep 08, 2025 am 01:20 AM

java

Problems and solutions to obtain JSP Session attribute as NULL

This article aims to solve the issue where the getAttribute() method returns NULL values ??when sharing JSP Session data between different browsers, such as IE and Edge. The article will dig into the scope concept of JSP and provide an effective way to share data between different browser sessions using Application scopes, while providing code examples and considerations to help developers understand and resolve such problems.

Sep 08, 2025 am 01:03 AM

Passing values ??from Thymeleaf to Controller that are not used in the view

This article describes how to use the Thymeleaf template engine to pass user identity information to the Controller in a Spring Boot project without explicitly displaying it in the view layer or having the user input. Through the @AuthenticationPrincipal annotation, you can directly obtain the identity information of the currently authenticated user in the Controller, thereby avoiding passing sensitive information in the view and simplifying code logic.

Sep 08, 2025 am 01:00 AM