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Understanding Java Volatile Keyword Semantics

The volatile keyword solves variable visibility and directive reordering problems in Java multithreading. 1. It ensures that all threads can be seen immediately after the variable is modified, and avoids threads from using cached old values; 2. It prevents the compiler and processor from reordering the operations involving volatile variables to ensure the order of operations; 3. It is suitable for scenarios where there is no atomicity, such as status flags, one-time safe release, independent variable assignment, etc.; 4. Unlike synchronized, the volatile lock-free mechanism does not guarantee the atomicity of composite operations, but is lighter and more efficient.

Jul 19, 2025 am 04:34 AM

Securing Java Microservices with OAuth2 and JWT

OAuth2 is responsible for authorization, and JWT is used to transmit information securely. The four roles of OAuth2 include resource owner, client, authentication server and resource server. The common process is the authorization code mode. After the user logs in, the client uses the code to exchange it for the token, and then uses the token to access the resources. JWT includes three parts: header, load and signature. The microservice confirms identity and resolves permission information by verifying the signature. SpringBoot integration uses the OAuth2ResourceServer module to configure issuer-uri and jwk-set-uri, and can customize the permission parser to extract the authorities. Notes include reasonable setting of token expiration time and security

Jul 19, 2025 am 03:59 AM

what is the 'final' keyword in java

In Java, the final keyword is used to restrict the modification of variables, methods, and classes to enhance code security and predictability. ① Variables declared as final cannot be changed once assigned, and are often used to define constants; ② Methods marked as final cannot be rewritten by subclasses to ensure that the logic is not changed; ③ Final class cannot be inherited to ensure that the implementation is not modified; ④ Uninitialized final variables (blank finals) can be assigned once in the constructor to improve flexibility and maintain invariance.

Jul 19, 2025 am 03:58 AM

Java Persistence API (JPA) Advanced Mappings

This article introduces four advanced mapping methods of JPA. 1. Bidirectional association specifies the relationship maintainer through mappedBy to achieve mutual access between User and Address; 2. Many-to-many association uses @ManyToMany and @JoinTable to manage intermediate tables, or manually create entity classes to expand intermediate table functions; 3. Embed objects use @Embeddable and @Embedded to embed Address into the Order table, supporting compound primary key design; 4. The inheritance structure uses SINGLE_TABLE, JOINED, and TABLE_PER_CLASS policies to map Employee subclasses, and select appropriate solutions according to query needs.

Jul 19, 2025 am 03:55 AM

java jpa

Domain-Driven Design (DDD) in Java Enterprise Applications

DDD is a business-centric design idea in Java enterprise applications and is suitable for complex business scenarios. 1. Core concepts include entities (with unique identification), value objects (without identification, only value view), aggregation (object boundary), and warehousing (aggregation-oriented access method). 2. The hierarchical structure should be clear: the user interface layer handles requests, the domain layer implements core logic, the infrastructure layer provides technical support, and the domain events are used to decouple. 3. When combined with SpringBoot, Entity and ValueObject are placed in the domain package as POJO. Repository defines the interface and implements it by infrastructure, DomainService and Applicati

Jul 19, 2025 am 03:55 AM

how to generate a random number in java

There are three main ways to generate random numbers in Java. First, use the Random class to generate integers, doubles or numerical values in a specific range, such as rand.nextInt(100) to generate integers from 0 to 99; second, use Math.random() to generate doubles from 0.0 to 1.0, and can generate integers through multiplication and casting; third, use Java 8 and above versions of ThreadLocalRandom, such as ThreadLocalRandom.current().nextInt(1,101) to generate integers from 1 to 100, which performs better in multithreaded environments. Select a combination according to specific requirements and Java version

Jul 19, 2025 am 03:54 AM

Java Messaging Queues (JMS) Advanced Concepts

Advanced concepts of JMS include message groups, message selectors, transaction and confirmation modes, and dead letter queues. The message group ensures that the same group of messages are processed by the same consumer through JMSXGroupID to ensure sequence; the message selector filters messages based on attributes, such as MessageConsumerconsumer=session.createConsumer(topic,"eventType='login'"); the transaction supports Session.SESSION_TRANSACTED mode, realizing the atomicity of sending and receiving operations; the dead letter queue captures multiple failed messages, facilitates subsequent analysis and retry, and improves the system's fault tolerance capabilities.

Jul 19, 2025 am 03:53 AM

Understanding Java Class Loading Mechanism

The Java class loading mechanism is the core of the runtime, and understanding it helps to troubleshoot class conflicts, class failure, and other problems. Its basic process is divided into three stages: loading, linking (verification, preparation, parsing) and initialization, and is loaded on demand using LazyLoading. Class loaders include BootstrapClassLoader, ExtensionClassLoader, ApplicationClassLoader and custom class loaders, and use the parent delegation model to ensure uniqueness and security. Frequently asked questions include ClassNotFoundException, NoClassDefFoundError, class duplicate loading, resource leakage, etc. Use suggestions include checking

Jul 19, 2025 am 03:52 AM

What is the volatile keyword in Java?

volatile is used in Java to ensure the visibility of variables between multiple threads. Its core role is to prohibit the JVM from local cache of variables and force read and write to directly interact with the main memory. Specifically: 1. volatile prevents CPU cache optimization to ensure that every read is retrieved from the main memory and refreshes to the main memory immediately after each write; 2. It is suitable for state flags, simple state switching and shared variable scenarios with more reads and fewer reads; 3. However, it cannot guarantee atomicity, such as compound operations (count) still require other synchronization mechanisms; 4. Its internal implementation prevents instructions from reordering and establishes memory barriers through happens-before rules; 5. It does not provide mutex function, but needs to be coordinated with synchronize.

Jul 19, 2025 am 03:49 AM

Java Security Hardening for Production Environments

When deploying Java applications to production environments, security reinforcement needs to start from five key points: 1. Restrict runtime permissions, use non-privileged users to start services, avoid abuse of root permissions, configure SecurityManager (depending on the situation), restrict file system permissions during containerized deployment, disable SpringBoot debug mode and sensitive endpoints; 2. Update dependency libraries and disable unsafe protocols, scan for third-party dependency vulnerabilities regularly, disable SSLv3 and TLS1.1 and below versions, force TLS1.2, enable HTTPS and forward confidentiality algorithms; 3. Handle logs and error messages carefully, avoid recording sensitive data, return general error codes uniformly, and disable stack information exposure; 4. Optimize J

Jul 19, 2025 am 03:47 AM

Security hardening java security

Java Message Queues for Asynchronous Communication

Message queue is a cross-process communication mechanism used to implement asynchronous processing, decoupling and traffic peak cutting. Its core functions include: 1. Decoupling the sender and the receiver; 2. Asynchronization improves the response speed; 3. Buffering high concurrent requests. The mainstream message queues in Java include RabbitMQ (suitable for scenarios with high reliability requirements), Kafka (suitable for high throughput scenarios), ActiveMQ (suitable for good compatibility but average performance) and RocketMQ (suitable for large-scale distributed systems). When using it, you need to pay attention to information loss, repeated consumption, performance tuning and operation and maintenance costs.

Jul 19, 2025 am 03:46 AM

What is the Diamond Operator in Java 7?

ThediamondoperatorinJava7simplifiesgenericclassinstantiationbyallowingtheomissionofredundanttypeparameters.BeforeJava7,developershadtospecifythesametypeinformationonbothsidesofanassignment,leadingtoverbosecode.Withthediamondoperator(),onlytheleft-han

Jul 19, 2025 am 03:44 AM

Java 7

Java Module System (Jigsaw) Best Practices

When using Java9 module system, you need to pay attention to naming specifications, packaging control, dependency management, automatic modules use and layered design. It is recommended to adopt a reverse domain name style such as com.example.mymodule to avoid conflicts and enhance recognition; try to be clear in semantics, do not use vague or duplicate names, and do not start with numbers or special characters. Exports and requirements should be clearly defined inside the module, only necessary packages should be exported, dependencies should be explicitly declared, and maintainability should be improved and coupling should be prevented. Be cautious when using automaticmodules, and give priority to modular libraries. If you have to use them, you should confirm the stability of their module name and avoid mapping conflicts. The correct configuration should be made in the build tool --m

Jul 19, 2025 am 03:30 AM

java jigsaw

Java Virtual Threads and Observability

Java virtual threads affect observability and monitoring strategies need to be adjusted to adapt. 1. The thread ID is no longer unique, and traditional tools are difficult to locate problems; 2. The thread name in the log is invalid, and MDC and distributed tracking are required to connect the request link; 3. The existing APM tools are insufficiently supported, so JDK should be upgraded and new tools such as JFR should be used; 4. The framework and community are gradually adapted, and we need to continue to pay attention to progress.

Jul 19, 2025 am 03:23 AM

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