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Android Tutorial: Read PDF files from specified folder and display in RecyclerView

This document is intended to guide Android developers how to read PDF files from a specified folder on the device and display them in a RecyclerView. We will cover the necessary permission requests, file readings, and how to display these files in RecyclerView to ensure that the code works properly in Android API 30 and above.

Sep 05, 2025 am 08:03 AM

How to print to the console in Java

Three methods of printing to the console in Java mainly use the System.out object: 1. Use System.out.println() to print messages and wrap them automatically, such as System.out.println("Hello,World!"); 2. Use System.out.print() to print content but not wrap them, so that the subsequent output is on the same line, such as continuously calling System.out.print("Hello,"); and System.out.print("World!"); will output Hello,Worl

Sep 05, 2025 am 07:48 AM

What is an ExecutorService in Java?

AnExecutorServiceinJavaisaconcurrencyutilitythatsimplifiesthreadmanagementbyusingthreadpoolstoefficientlyexecutetasks.Itprovideskeybenefitssuchasthreadreuse,resourcemanagement,simplifiedtasksubmission,andgracefulshutdown.CreatedviatheExecutorsfactory

Sep 05, 2025 am 07:30 AM

Implementing Caching Strategies in a High-Performance Java Application

Choosetherightcachingtypebasedonusecase:uselocalcachinglikeCaffeineforread-heavystaticdatawithinasingleJVM,distributedcachinglikeRedisforclusteredenvironments,andCDNcachingforstaticassets.2.UseCaffeineforhigh-performancelocalcachingwithfeatureslikesi

Sep 05, 2025 am 07:26 AM

Tutorial on flexible conversion of date and time string format in Java

This tutorial details how to accurately convert date and time strings in many different formats into a unified "DD.MM.YYYY" format using Java 8 and later. The article highlights the advantages of modern datetime APIs, parses the correct usage of DateTimeFormatter pattern symbols, and provides complete sample code and best practices for handling time zone information, local time, and non-standard format strings to help developers avoid common format parsing errors.

Sep 05, 2025 am 06:33 AM

Implementing OAuth 2.0 and JWT in Java Spring Security

Add SpringSecurity, OAuth2 client, resource server and JJWT dependencies; 2. Configure OAuth2 client registration information such as Google or GitHub in application.yml; 3. Configure the resource server to use JWT, and use issuer-uri or custom JwtDecoder; 4. Create the JwtUtil tool class to generate and verify JWT tokens; 5. Implement JwtAuthenticationFilter to intercept requests and parse Bearer tokens; 6. Disable CSRF in SecurityConfig, enable stateless sessions, configure OAuth2 login and add JWT filtering

Sep 05, 2025 am 06:29 AM

Create a secure and digitally qualified PIN input box in Codename One

This tutorial will guide you how to create a PIN input box in the Codename One app that is both safe and accepts digital input only. We will explore the constraint method of TextComponent in depth, correct the normal wrong usage, and show how to correctly combine NUMERIC and PASSWORD constraints through bit operations to achieve user interface components that meet PIN input requirements.

Sep 05, 2025 am 05:36 AM

How to handle errors in CompletableFuture in Java

Useexceptionally()toprovideafallbackvaluewhenanexceptionoccurs,allowinggracefulrecoverybyreturningadefaultresult.2.Usehandle()tomanagebothsuccessandfailureinasinglestage,enablingtransformationorloggingwhileensuringthechaincontinues.3.UsewhenComplete(

Sep 05, 2025 am 05:23 AM

Spring Boot MockMvc Test: How to pass JSON request body to REST interface

This article introduces in detail how to use MockMvc to unit test the REST interface that receives JSON request bodies in Spring Boot applications. The core steps include creating a data transfer object (DTO), converting it into a JSON string using Jackson's ObjectMapper, and sending JSON data as a request body through MockMvc's contentType() and content() methods to ensure the accuracy and validity of the test.

Sep 05, 2025 am 05:09 AM

What are regular expressions in Java?

RegularexpressionsinJavaareusedforpattern-basedstringoperationssuchasmatching,searching,andmanipulation,primarilythroughthejava.util.regexpackage'sPatternandMatcherclasses,wherePatterncompilestheregexandMatcherappliesittostrings,enablingefficienttext

Sep 05, 2025 am 04:53 AM

How to create a record in Java

In Java 16 and above, the correct way to create a record is to use the record keyword to define the immutable data carrier class. 1. Declare record with publicrecordPerson(Stringname,intage){} to automatically obtain private final fields, constructors, accessors, equals, hashCode and toString; 2. You can add custom methods such as isAdult(); 3. You cannot define additional instance fields (except static); 4. In the old version, you need to manually create final classes and implement fields, constructors, getters and equals/hashCode/toStr.

Sep 05, 2025 am 04:51 AM

Fix 'Teen Talk' program: Solve infinite loop problem

This article aims to help beginners fix infinite looping problems in a Java program called "Teen Talk". The program is designed to simulate spoken teenagers by adding "like" after each word of the string is entered. By analyzing the error code, we will find out the root cause of the program being stuck and provide a revised code example to ensure that the program runs correctly and outputs the expected results.

Sep 05, 2025 am 04:33 AM

How to create a thread in Java

There are four main ways to create threads: 1. Inherit the Thread class and rewrite the run() method, and start the thread through start(); 2. Implement the Runnable interface, pass the task to the Thread constructor, and realize the decoupling of the task and the thread; 3. Use Lambda expressions to simplify the implementation of Runnable, making the code more concise; 4. Use ExecutorService thread pool to manage threads, which is recommended for production environments, submit tasks through submit() and call shutdown() to release resources. Start() should always be called instead of run(), with Runnable or thread pool priority for flexibility and performance, the final answer is: Recommended

Sep 05, 2025 am 04:31 AM

Advanced Java Concurrency and Multithreading

Synchronized ensures atomicity, visibility and orderliness, volatile only guarantees visibility and prohibits reordering but does not guarantee atomicity; 2. Use atomic classes such as AtomicInteger to achieve lock-free thread-safe operation based on CAS; 3. ReentrantLock provides more flexible lock control than synchronized, including interruptible, timeout, fair locking and conditional variables; 4. Thread pools should be manually created through ThreadPoolExecutor to clarify core parameters and avoid the hidden risks of Executors; 5. Concurrent collections such as ConcurrentHashMap, CopyOnWriteArrayList and Blo

Sep 05, 2025 am 03:55 AM