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Building a Real-Time Chat Application with Java and WebSockets

The key steps in building a live chat application using Java and WebSockets include: 1) Defining WebSocket endpoints through @ServerEndpoint; 2) Using @OnOpen, @OnMessage and other annotations to handle lifecycle events; 3) Maintaining session collections and broadcasting messages in the ChatEndpoint class; 4) The front-end connects ws://localhost:8080/your-app/chat through JavaScript and sends and receives messages; 5) Using Maven to manage dependencies and deploy the application to Tomcat; 6) After starting Tomcat, test real-time communication in multiple browser windows. Complete implementation includes backend session tube

Jul 24, 2025 am 12:52 AM

how to check java version in cmd

To check the Java version, you can use the java-version command in CMD to view the JRE version used by the current system. If you need to view the JDK compiler version, use javac-version; if the command cannot be recognized, it may be that Java is not installed or environment variables are not configured, you need to go to the official website to download and install and add the Java bin directory to the system PATH; if multiple Java versions are installed, you can view the path order through the wherejava command, and switch the default version by modifying PATH or using the version management tool.

Jul 24, 2025 am 12:39 AM

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Optimizing Java JDBC Database Interactions

Use connection pooling, PreparedStatement and batching, shutting down resources, adjusting transaction boundaries and isolation levels to optimize JDBC performance. 1. Use connection pools (such as HikariCP) to reduce the overhead of frequently creating connections; 2. Use PreparedStatement to prevent SQL injection and improve execution efficiency, and combine batch processing to improve batch operation throughput; 3. Use try-with-resources to ensure that resources are automatically closed to avoid memory leaks; 4. Adjust transaction boundaries, close auto-commit and commit uniformly, and select appropriate transaction isolation levels based on the business to reduce lock competition.

Jul 24, 2025 am 12:21 AM

How to get the current date and time in Java 8?

In Java 8, you recommend using the classes in the java.time package; 1. Get the full date and time to use LocalDateTime.now(); 2. Get the date only with LocalDate.now(); 3. Get the time only with LocalTime.now(); 4. Format output needs to be matched with DateTimeFormatter; 5. Specify the time zone and pass the ZoneId parameters, such as ZoneId.of("Asia/Shanghai"); these are more intuitive, thread-safe and easier to use than the old Date and Calendar.

Jul 23, 2025 am 04:06 AM

How to read Java bytecode?

To understand Javabytecode, you can use the JDK-provided Javap tool to disassemble the bytecode to view the bytecode; 1. Use javac to compile the class file and view the method instruction list through the javap-c command; 2. Understand the stack-based bytecode structure and the operating mechanisms of common instructions such as iconst, store, iload, iadd, etc.; 3. You can use graphical tools such as BytecodeViewer or IDE plug-in to assist in analyzing the class structure and field information; 4. Pay attention to the actual conversion form of Java syntax sugar in bytecode, such as switch string support, try-with-resources and lambda expressions. Mastering these key points is helpful

Jul 23, 2025 am 04:05 AM

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how to sort an array in java

A common way to sort arrays in Java is to use Arrays.sort(). For basic data type arrays, such as int[] or double[], call Arrays.sort() directly to achieve ascending sort; if you need to sort in descending order, you need to use a wrapper class (such as Integer) and pass it into the Collections.reverseOrder() comparator. String arrays are sorted in dictionary order by default, and case-insensitive sorting can be achieved through String.CASE_INSENSITIVE_ORDER. When sorting custom object arrays, you need to make the class implement a Comparable interface or provide a Comparator, for example, according to Pe

Jul 23, 2025 am 04:03 AM

Java Blockchain Development: Smart Contracts and DLT

To develop blockchain in Java, the focus is on smart contract interaction and distributed ledger technology (DLT) applications. 1. Although Java does not directly write smart contracts, HyperledgerFabric's Chaincode can be called through SDK (such as fabric-gateway-java); 2. Java is suitable for building intermediate-layer services based on HyperledgerFabric and Corda, supporting business logic encapsulation, permission control, etc.; 3. During development, you need to pay attention to key details such as SDK version matching, identity authentication configuration, log debugging and performance optimization. By mastering these key points, Java developers can effectively carry out their work in enterprise-level blockchain projects.

Jul 23, 2025 am 04:00 AM

Implementing Event-Driven Architecture with Java and Apache Kafka

Understand core components: Producers publish events to Topics, Consumers subscribe and process events, KafkaBroker manages message storage and delivery; 2. Locally build Kafka: Use Docker to quickly start ZooKeeper and Kafka services, expose port 9092; 3. Java integration Kafka: introduce kafka-clients dependencies, or use SpringKafka to improve development efficiency; 4. Write Producer: configure KafkaProducer to send JSON format order events to orders topic; 5. Write Consumer: Subscribe to o through KafkaConsumer

Jul 23, 2025 am 03:51 AM

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Surviving the Java Coding Interview: Data Structures and Algorithms

Master the core data structure and its applicable scenarios, such as the selection of HashMap and TreeMap, and the expansion mechanism of ArrayList; 2. Practice algorithms from the Java perspective, proficient in double pointer, sliding window, DFS/BFS and other modes and can be clearly implemented; 3. Write clean and robust Java code, pay attention to naming, boundary processing and language features (such as generics and final); 4. Prepare the practical question of "why use Java" and understand the impact of StringBuilder, GC, etc. on performance; maintain practice and clear expression to stand out.

Jul 23, 2025 am 03:46 AM

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Implementing Event-Driven Architecture with Java Kafka

The core points of using Java and Kafka to implement event-driven architecture include: 1. Design a clear event model, use Avro SchemaRegistry to manage structure changes, unify naming specifications and include necessary information; 2. Set reliability parameters, asynchronous sending and log callbacks when building producers, and consumers use Group to achieve expansion, control offset submission and idempotence processing; 3. Use KafkaStreams to implement real-time processing logic, such as window aggregation statistics; 4. Design an error retry mechanism, catch exceptions and retry failure messages, use DLQ to handle multiple failure events, and improve system robustness.

Jul 23, 2025 am 03:43 AM

Mastering the Builder Design Pattern in Java

The Builder mode solves the problem of too many construct parameters and mutability by building complex objects in step by step; 2. When implementing, set the class to final and initialize the fields through Builder in a private construct; 3. Create a static internal Builder class, and each setting method returns this to support chain calls; 4. Verify the required fields in build() to ensure object consistency; 5. Applicable to multiple parameters, especially objects with optional parameters, to improve readability and maintenance, and avoid telescoping constructors or destroying immutability setters.

Jul 23, 2025 am 03:42 AM

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Static Code Analysis for Improving Java Code Quality with SonarQube

SonarQube detects pre-run vulnerabilities such as null pointers and resource leaks, and integrates CI/CD to automatically analyze PR; 2. Prevent security risks such as hard-coded passwords and unsafe random numbers through OWASP rules, and use SecurityHotspots to enhance team security awareness; 3. Detect code odor, duplicate code, irregular naming problems, reduce cognitive burden, and improve maintainability; 4. Track technical debt and test coverage, monitor coverage >80%, repeat rate

Jul 23, 2025 am 03:37 AM

What is the 'static' keyword in Java used for?

In Java, the static keyword is used to create class-level variables and methods, allowing direct access without instantiation of objects. 1. The static variable is shared by all instances, and modifying it in one place will affect all instances; 2. The static method can be called directly without creating objects, and is suitable for tool classes or constant operations; 3. The static block is used for initialization operations during class loading, such as configuration reading; 4. Be cautious when using it to avoid excessive use and difficult to maintain memory problems and code.

Jul 23, 2025 am 03:36 AM

how to compile and run a java program from command line

TocompileandrunaJavaprogramfromthecommandline,firstensuretheJDKisinstalledandconfigured.1.Checkinstallationbyrunningjavac-versionandjava-version.2.Ifnotinstalled,downloadandinstalltheJDKandsetthePATHenvironmentvariable.3.CompiletheJavafileusingjavacH

Jul 23, 2025 am 03:35 AM