This article demonstrates how to use the iTextPdf library in a Java SpringBoot project to create PDF templates, dynamically fill fixed and tabular invoice data, generate separate PDFs, and merge them into a single document, providing complete code examples and configuration details.
Because phone numbers are identifiers that can contain symbols and exceed the numeric range of an int, storing them as a String—despite higher memory use—is semantically correct, avoids overflow, preserves formatting, and benefits from JVM string pooling, making String the preferred type in most Java applications.
This article explains the LeetCode Combination Sum II problem, detailing how to find all unique candidate combinations that sum to a target using sorting and backtracking while eliminating duplicate results, and provides complete implementations in Java, C++, C, and Python.
This article explains the CQRS pattern, its origins, benefits, and challenges, and provides a step‑by‑step guide with Java code examples on how to implement CQRS, event sourcing, and asynchronous communication using Spring Boot, Axon, and Kafka in microservice architectures.
This article provides a comprehensive guide to Java thread pools, explaining their purpose, construction parameters, execution flow, worker reuse, task retrieval with timeout, lifecycle states, shutdown mechanisms, monitoring methods, and best practices for customizing pools in real-world projects.
This guide explains common scenarios for using custom Java annotations—such as logging, permission control, data validation, and caching—and walks through the step-by-step process of defining an annotation, applying it in Spring services, handling it with an AOP aspect, and testing the implementation in a Spring Boot application.
This guide shows how to use JSONPath within a Spring Boot 3.4.0 project to efficiently query, filter, and modify complex JSON structures, providing Maven setup, syntax overview, operator tables, and practical code examples for extracting authors, prices, books, and applying custom filters.
The Concept‑Download library lets SpringBoot developers replace verbose download code with a single @Download annotation that automatically handles classpath resources, local files, HTTP URLs, custom objects, compression and reactive streaming, simplifying batch and QR‑code ZIP exports.
This article introduces several advanced IntelliJ IDEA debugging techniques—including Evaluate and Log at breakpoints, field breakpoints, exception breakpoints, and method breakpoints—providing step‑by‑step instructions, code examples, and screenshots to help Java developers debug more efficiently without cluttering source code.
This article showcases a collection of over 100 practical Spring Boot 3 examples, focusing on modern Java Stream techniques such as Stream.ofNullable for null safety, Stream.iterate for infinite sequences, advanced collectors like collectingAndThen, takeWhile/dropWhile, teeing, and summarizingLong, each illustrated with concise code snippets.
Fast‑Retry is a high‑performance Java library that enables asynchronous, multi‑task retry with customizable policies, offering dramatically better throughput than traditional synchronous retry frameworks like Spring‑Retry and Guava‑Retry for large‑scale user‑identity polling scenarios.
This article provides a comprehensive guide to Java I/O streams, covering the distinction between node (low‑level) and processing (high‑level) streams, byte versus character streams, their superclasses, common implementations, buffering techniques, object serialization, and practical code examples for reading and writing data.
The article explains the concept of Rump‑Up in performance testing, details the steps to modify multithreaded task and executor classes, and provides Java code examples that enable gradual load increase and controlled data collection for more accurate bottleneck identification.
This article explains Redis Pipeline—a technique that batches multiple commands in a single request to cut round‑trip latency, details how to implement it in Java using Jedis, and outlines its advantages, drawbacks, and ideal scenarios for high‑throughput backend applications.
The article explains how excessive if‑else logic in multi‑business middle‑platforms leads to maintenance nightmares and demonstrates, with concrete code and a real open‑source project, how a flow engine and plugin‑extension framework provide clean isolation, extensibility, and reliable execution of business processes.
This article provides a detailed tutorial on using Maven for Java projects, covering basic configuration, repository setup, dependency management, module organization, plugin usage such as jar, assembly, and shade, as well as build settings and code examples.
This article examines how Java Stream and Lambda, while powerful for concise data processing, can become cumbersome when misused, and provides practical tips such as proper line breaks, function extraction, careful filter logic, safe Optional handling, and cautious use of parallel streams to keep code readable and maintainable.
This article introduces MybatisX, an IntelliJ IDEA plugin that streamlines MyBatis and MyBatis‑Plus development, and provides a detailed step‑by‑step tutorial on setting up a Spring Boot project, configuring the database, generating code, and writing a simple controller using MyBatis‑Plus.
The article explains why excessive conditional logic harms maintainability, introduces a flow‑engine and plugin‑extension architecture to isolate business code, demonstrates configuration and execution with Java examples from the open‑source MemberClub project, and lists the surrounding tech stack for practical learning.
This article explains the concept of Single Sign-On, its advantages, and two practical implementations using ticket‑based authentication and encrypted user data exchange between Service A and Service B, complete with database schema, configuration files, and full Java code examples.
Even when you replace HashMap with ConcurrentHashMap and use ThreadLocal for per‑thread data, hidden pitfalls in thread‑pooled environments can cause data leakage and race conditions, but proper cleanup and atomic operations can restore safety, as demonstrated with concrete Java examples.
This article walks through the problem of locking out users after multiple failed login attempts, explains why IP‑based locking with Redis and Lua scripts is effective, and provides a complete Spring Boot implementation—including front‑end HTML, custom annotations, AOP aspect, Redis configuration, and sample controller code—to enforce a configurable login‑attempt limit.
This article explains the purpose, usage patterns, and internal mechanics of Spring's @Import annotation, including importing regular classes, ImportSelector implementations, and ImportBeanDefinitionRegistrar implementations, with complete code examples and a discussion of how Spring processes these imports at runtime.
The article demonstrates how to refactor a large PHP API suite into a Java Spring MVC application by creating a generic AggregateController that, through model‑name mapping, reflection‑based repository registration and a thread‑safe MappingKit, provides CRUD endpoints for any table, collapsing hundreds of endpoints into just two controllers for client and admin.
This guide walks Java developers through preparing the environment, installing the CodeGPT plugin, configuring DeepSeek API keys and models, and using the AI assistant for code generation, completion, explanation, and troubleshooting within IntelliJ IDEA, complete with screenshots and sample code.
DeepSeek4j 1.4 introduces a Java‑native framework that fully preserves DeepSeek's chain‑of‑thought and billing features, adds reactive streaming support, and provides a Spring Boot starter for effortless integration, accompanied by quick‑start code, configuration examples, and a built‑in debugging UI.
This article explains why Lombok's @Builder annotation ignores field default values in Java classes, demonstrates the issue with sample code, and shows how using @Builder.Default resolves the problem by generating static default methods in the compiled builder class.
This article explains how Java handles string literals and the new String() constructor, detailing when objects are created in the string constant pool versus the heap, and demonstrates the resulting reference comparisons with code examples.
This article explains the design and Java Spring‑Boot implementation of a business transaction ID generator that combines business type, date, random digits and a non‑sequential long integer, discusses database schema, concurrency handling, performance testing, and potential duplication pitfalls.
This article records and analyzes how upgrading an application to JDK 11 changed the Direct Memory management strategy, causing a sharp increase in memory‑utilization alerts, and demonstrates step‑by‑step troubleshooting, code inspection, and JVM parameter tuning to restore normal memory usage.
This article provides a comprehensive guide to IntelliJ IDEA, covering basic operations, advanced shortcuts, Maven integration, debugging, hot‑reload settings, and various UI customizations, offering developers practical tips and code snippets to boost Java development efficiency.
This article explains how SpringBoot's default Tomcat container can be swapped for the high‑performance Undertow server, details Undertow's characteristics, provides Maven configuration steps with code snippets, and presents benchmark results showing superior throughput and lower memory usage for high‑concurrency applications.
This tutorial explains what Spring AI is, walks through creating a Spring Boot project with Maven, adding the necessary dependencies, writing a simple controller that forwards user messages to a local DeepSeek model, configuring the application, and testing the AI‑powered endpoint.
This article introduces the URule rule engine, explains its core concepts, shows how to install and configure it in a Spring Boot project, demonstrates library definitions, rule set creation (wizard and script modes), decision table usage, and provides real‑world scenario code examples for backend developers.
The article explains why existing Java AI frameworks struggle with DeepSeek R1’s chain‑of‑thought and streaming features, introduces DeepSeek4j 1.4 as a targeted solution, details its core capabilities, and provides a step‑by‑step guide to integrate it with Spring Boot and Project Reactor.
This article explains the default Tomcat settings in Spring Boot 2.7.10, details core parameters such as connection queue length, max connections, thread pool sizes, keep-alive and timeout options, and demonstrates how to inspect and test these configurations with code examples and command-line tools.
This article walks through creating a fully automated Spring Boot and MyBatis code generator using Freemarker templates, detailing each step from extracting table metadata to generating DAO, service, controller, and entity classes, and shows how a single-table CRUD can be produced in seconds.
This tutorial explains how to implement dynamic master‑slave MySQL switching in a SpringBoot 3.0.4 project using AOP and a custom @DataSource annotation, covering configuration, enum definitions, utility classes, aspect handling, and usage examples for both single and multiple data sources, including Oracle integration.
This article introduces a Spring Boot 3 case collection with over 100 permanent examples and then provides a complete tutorial on implementing audit logging using Spring AOP, SpEL, asynchronous processing, custom annotations, JPA entities, and batch persistence to efficiently record operation details.
This tutorial walks you through creating a Java‑based AI chat agent using Spring AI Alibaba, integrating Alibaba Cloud's large language model, adding function‑calling for weather queries, and enabling full observability with ARMS in a cloud‑native deployment.
This article explains why the "class file has wrong version" error occurs when Java compilation and runtime versions differ, shows the mapping between Java releases and class file versions, demonstrates the error with sample code, and provides step‑by‑step solutions including version checks, Maven configuration, IDE settings, and best‑practice recommendations.
The JD App backend hotkey framework provides millisecond‑level detection of bursty hot data, users, and interfaces, pushes the hot keys to all JVMs in the cluster, and dramatically reduces database query pressure while improving overall application performance.
This article demonstrates how Java 8’s functional interfaces, such as Function and SFunction, can be leveraged to refactor repetitive data validation logic, introducing generic methods like ensureColumnValueValid and validateColumnValueMatchesExpected that improve code reuse, readability, and maintainability in backend services.
The article explains how automatic @Autowired injection can tightly couple domain models to the Spring container, hide dependencies, hinder testing, create circular‑dependency risks, and violate clean architecture, then demonstrates an explicit‑dependency approach with a custom SpringContext utility, compares both methods, and offers practical guidelines for layered design and testing.
This article introduces Java 8's Optional class, explains its creation methods and common operations such as get, isPresent, ifPresent, filter, map, flatMap, orElse, orElseGet, orElseThrow, and shows practical usage scenarios and best‑practice recommendations for handling null values in backend code.
This article explains how Java’s ArrayList uses the transient keyword during serialization to skip the underlying array, reducing redundant data, and details the custom writeObject and readObject methods that ensure only actual elements are stored and restored efficiently.
This article introduces the Fabric8 KubernetesClient for Java, explains why it outperforms the official client, shows how to add the Maven dependency, and provides step‑by‑step code examples for listing, creating, deleting, and watching Pods, as well as advanced operations on ConfigMaps, Deployments, and custom resources, illustrating real‑world use cases such as log collection, self‑healing, and dynamic scaling.
This article explains the concept and benefits of logical deletion, then demonstrates how to implement it in Spring Boot 3 using JPA annotations like @SQLDelete and @SoftDelete, and MyBatis‑Plus configuration, complete with code examples and SQL output.
This article explains how Caffeine implements element expiration using three built‑in policies and a custom TimeWheel strategy, detailing the construction of the timer wheel, bucket selection, scheduling, advancing, and eviction logic within the cache's maintenance cycle.
This tutorial walks Java developers through the complete workflow of building, training, and evaluating a neural network in PyTorch, covering network definition, data iteration, forward and backward passes, loss calculation, and parameter updates with detailed code examples and Java‑centric analogies.
This guide walks you through creating a Spring Boot project, configuring DeepSeek's large language model via SiliconFlow, setting up OpenAI‑compatible parameters, and implementing a REST controller that returns weather forecasts using the model, complete with step‑by‑step code snippets, configuration files, and deployment instructions.
The article shares DJI's impressive compensation data, details a 50‑minute Java backend interview covering concurrency tools, locks, CountDownLatch, ConcurrentHashMap, Kafka ordering, zero‑copy, Spring AOP, filters vs. interceptors, and provides code examples and explanations for each concept.
This article explains two design approaches for handling test data in a multithreaded performance testing engine, compares their trade‑offs, and provides complete Java code for data aggregation, statistical analysis, TPS calculation, and refactoring the tool for cleaner extensibility.
This article explains how to design a modular Spring Boot backend management system called XiaoLe, covering essential design principles such as single responsibility, high cohesion, low coupling, reusability, clear interfaces, layered architecture, and testability, and provides detailed Maven module structures and POM configurations for each component.
This article introduces Jython, explains its features, provides step‑by‑step installation instructions, demonstrates how to run Python code on the Java platform and how Java can invoke Jython scripts, and outlines common application scenarios for this Python‑Java bridge.
The article examines the trade‑offs of using Java's primitive int versus the String class to store phone numbers, covering memory usage, JVM bytecode behavior, data semantics, and practical performance implications for large‑scale systems.
The article introduces DeepSeek4j 1.4, a Java‑based framework that overcomes Spring AI’s limitations by fully preserving DeepSeek’s chain‑of‑thought and billing features, adding reactive streaming, providing Spring Boot starter integration, and offering quick‑start code samples and configuration guidance.
This article explains how to integrate DeepSeek's large language models into a Spring AI application, covering model selection, API key configuration, URL setup, dependency inclusion, and providing complete Java code examples for both synchronous and streaming chat interactions.
This article compares JWT and session authentication, discusses their differences, advantages, security and performance considerations, and provides a complete Java implementation with Redis integration, including token generation, validation, renewal, and interceptor configuration for secure backend services.
This article explains the purpose of Java's Thread.start() method, demonstrates what happens when it is invoked twice, shows the resulting IllegalThreadStateException, and provides a detailed analysis of the start() source code to clarify the thread lifecycle.
FastClasspathScanner (formerly ClassGraph) is a high-performance Java library that dramatically speeds up classpath scanning by using multithreaded processing, smart caching, and efficient handling of complex hierarchies, making reflection-heavy frameworks, plugin systems, web applications, and code-analysis tools faster and more memory-efficient.
This article introduces a comprehensive Spring Boot 3 case collection and provides a detailed guide on using @ConfigurationProperties, constructor binding, @DefaultValue, and record types for type‑safe configuration, including examples of nested properties, collections, and default values, while promising ongoing updates and free source code for subscribers.
This article explains critical pitfalls, graceful shutdown requirements, startup timing issues, suitable business scenarios, and reliability techniques—including retries, idempotency, and integration with Kafka and MQ—when applying Spring Event for publish‑subscribe patterns in high‑traffic backend services.
This article explains how to make custom classes visible to Spring Boot by loading external JAR files through four methods—extending the classpath, using Spring Boot's loader.path parameter, creating a custom ClassLoader, and modifying the boot classpath—while also showing how to configure scanning and packaging details.
This article explores how Java 8 streams and lambda expressions can make code shorter and more elegant, while highlighting common mistakes such as poor formatting, oversized functions, misuse of Optional, and over‑reliance on parallel streams, and offers practical guidelines for writing readable, maintainable backend code.
This article explains how Java's ThreadPoolExecutor ensures core threads stay alive by analyzing the execute, addWorker, runWorker, and getTask methods, detailing the dead‑loop logic, timeout handling, and the conditions under which core threads can be reclaimed.
This article explains the Chain of Responsibility design pattern, demonstrates its application in multi‑step product validation and expense‑approval workflows with detailed Java code, configuration handling, Spring bean injection, and discusses its advantages and drawbacks.
This article explains the Java memory model, outlines common OutOfMemoryError types, and provides a step‑by‑step guide for diagnosing, fixing, and preventing memory‑related issues in large‑scale Java applications, including heap, metaspace, and stack analysis, JVM flag tuning, and best‑practice recommendations for resource handling and monitoring.
This article walks through designing and implementing a Java multithreaded execution class for performance testing, covering thread‑pool creation, task coordination with CountDownLatch, start/stop control, and a complete demo that runs concurrent tasks with timed logging.
This article investigates whether the JVM terminates when a thread encounters an OutOfMemoryError, demonstrating through Spring Boot controllers and multithreaded examples how main and child threads, daemon settings, and explicit OOM handling affect JVM shutdown behavior.
This guide walks Java developers through preparing the environment, installing the CodeGPT plugin, configuring DeepSeek API keys, and using the AI-powered code assistant within IntelliJ IDEA, including code completion, explanation, and question‑answer features, with usage statistics and sample code.
The article explains how to use Apache Commons Pool to create reusable object pools in Java—showing Maven setup, a custom PooledObjectFactory, pool configuration, borrowing and returning objects, and demonstrates a Redis Jedis connection pool built on the same framework while detailing the pool’s initialization, borrowing, and return mechanisms.
This article provides a comprehensive walkthrough of Caffeine cache's architecture, explaining its fixed-size eviction policy, underlying data structures such as ConcurrentHashMap, MPSC buffers, Count‑Min Sketch frequency tracking, and the dynamic window‑probation‑protected zones, while detailing key methods like put, getIfPresent, and maintenance.
Spring Security 6.4 introduces One-Time Token Login, allowing users to authenticate via a magic link sent by email instead of passwords; the article explains its core concepts, token lifecycle, essential components, and provides step‑by‑step code examples for configuring and implementing this secure, user‑friendly authentication method.
This article explains why modifying a List inside a foreach loop causes ConcurrentModificationException, shows the proper ways to remove elements using iterators or lambda expressions, warns against casting subList to ArrayList, clarifies correct toArray and Arrays.asList usage, compares LinkedList and ArrayList performance, and recommends the most efficient traversal techniques.
This article explains Java's ClassLoader mechanism, its loading, linking, and initialization phases, the parent‑delegation hierarchy, common problems such as ClassNotFoundException and OOM, and provides practical troubleshooting steps and best practices for managing dynamic class loading.
This guide showcases nine distinct Spring Boot 3 API development techniques—from classic @RestController annotations to functional RouterFunction beans and custom Actuator endpoints—providing complete code samples, configuration details, and a promise of ongoing updates with a downloadable PDF of over 90 practical cases.
This article introduces LiteFlow, a lightweight yet powerful Java rule engine, explains its architecture, component types, EL rule file syntax, configuration options, and demonstrates a real‑world e‑commerce workflow example, providing code snippets and deployment tips for backend developers.
The article explains how Java's synchronized keyword works only within a single JVM, why it fails to provide mutual exclusion across multiple processes in distributed systems, and presents alternative distributed locking mechanisms such as database locks and Redis-based locks with code examples.
This article explains how to obtain a DeepSeek API key, configure Spring AI with the appropriate base URL and model, and provides Java code examples for both synchronous and streaming chat interactions using the DeepSeek large‑language model.
This article introduces LiteFlow, a lightweight yet powerful rule engine for Spring Boot, explains its architecture, supported rule formats, core components, EL rule files, data context handling, configuration options, and demonstrates a real‑world e‑commerce order processing workflow with code examples.
This guide explains why VARCHAR, float, and double are unsuitable for monetary values, and recommends using BIGINT/Long for cent‑level precision or BigDecimal/DECIMAL for higher precision, with practical tips and code examples for Java and MySQL.
This article explores why Spring MVC automatically binds HTTP header values to controller method parameters, demonstrates the issue with a sample Spring Boot 3.4.0 project, analyzes the underlying HandlerMethodArgumentResolver and ServletModelAttributeMethodProcessor code, and provides two practical solutions to prevent unwanted header binding.
This article demonstrates how to use Java 8 functional interfaces, especially Function and the MyBatis‑Plus SFunction wrapper, to eliminate repetitive data‑validation code, improve readability, and create reusable validation utilities for backend services.
The program that loops on a non‑volatile boolean flag sometimes terminates because changing the counter to a volatile int or to an Integer causes the JVM to emit hidden memory barriers on reference writes, making the flag visible, but this behavior is JVM‑specific and not a reliable substitute for declaring the flag volatile.
This article explores a classic Java concurrency puzzle where a non‑volatile flag causes an infinite loop, examines how modifying the loop variable from int to Integer or adding volatile affects termination, and explains the underlying JVM memory‑barrier behavior revealed by DeepSeek.
This article explores how mutating the fields of an object used as a HashMap key corrupts its hash code, causing look‑ups to fail, and walks through the underlying source code of put, hash, getNode and related methods to reveal why this happens.
This article explains how Agrona's lightweight AgentRunner replaces the standard Java ExecutorService to manage long‑running tasks with minimal thread‑context switching, using the Agent model and customizable IdleStrategy to achieve high throughput and low latency in concurrent Java systems.
This article walks through installing Ollama, downloading the DeepSeek‑r1:1.5b model, configuring Spring AI in a Spring Boot 3 project, and exposing the model via a REST endpoint with Server‑Sent Events, providing complete code snippets and step‑by‑step screenshots for a functional AI integration.
This article explains how ThreadLocal stores values per thread, details the internal set and get mechanisms, discusses potential memory‑leak problems caused by stale entries, and provides best‑practice guidelines such as using remove() and InheritableThreadLocal for child threads.
This article introduces the Java JSch library for Spring Boot 3, demonstrating how to read remote files without downloading, execute commands on a remote host, and obtain an interactive shell prompt, complete with Maven dependency setup, code examples, and execution results, while promising ongoing updates to the case collection.
This guide walks you through downloading Byteman, setting up BYTEMAN_HOME, using Ant or Maven for integration, building from source, configuring the Java agent with detailed options, and leveraging tutorials for effective fault‑injection testing in Java applications.
This article explains the LeetCode 75 "Sort Colors" challenge, detailing the problem statement, constraints, a three‑pointer Dutch National Flag solution, and provides complete implementations in Java, C++, C, and Python without using built‑in sorting functions.
The article presents a comprehensive design for securing third‑party API calls by generating unique Access Key/Secret Key pairs, defining permission scopes, implementing signature generation and verification, employing timestamps and nonces to prevent replay attacks, and outlining practical API endpoint specifications and response standards.
This article explains how the @TableLogic annotation in MyBatis-Plus implements logical deletion by converting delete operations into updates, details its parameters, supported field types, global configuration, and provides complete Java and SQL code examples for practical usage.
This comprehensive guide covers RabbitMQ fundamentals, installation on Windows, Linux, and Docker, configuration for durability and monitoring, Java integration examples, high‑availability architectures, clustering, and practical troubleshooting tips for building reliable distributed systems.
This article explains the differences and usage of Apache Commons Lang3 StringUtils methods such as isEmpty, isNotEmpty, isAnyEmpty, isNoneEmpty, isBlank, isNotBlank, isAnyBlank, and isNoneBlank, providing code examples and behavioral details for handling null, empty, and whitespace strings in Java.
This article introduces the Liteflow lightweight rule engine for Java, explains its architecture, configuration, component types, EL rule file syntax, data context handling, and demonstrates a practical e‑commerce workflow, highlighting hot‑deployment and performance benefits for backend development.
This article demonstrates how to improve the performance of nested for‑loops that match user IDs between two large lists by adding a break statement and by converting the inner list into a hash map, reducing execution time from tens of seconds to a few seconds.
This tutorial explains China’s electronic‑seal regulations, shows how to generate a CA‑based X.509 certificate and a custom seal image with BouncyCastle, and demonstrates signing a PDF in Java using iText 5 to embed a visible seal and a verifiable digital signature.
