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How to connect to and use Redis with Java (e.g., using Jedis or Lettuce)?

To connect and use Redis in Java, you can choose Jedis or Lettuce client. 1.Jedis is simple and lightweight, suitable for small projects. You need to add dependencies and connect and operate Redis using synchronous methods; 2. Lettuce is more modern and supports asynchronous operations. You need to add dependencies and create connections through RedisClient and use synchronous or asynchronous APIs; 3. General recommendations include using connection pools, handling exceptions, serializing complex objects, and monitoring memory usage. The two solutions have their own advantages, and the choice depends on the specific needs.

Jul 11, 2025 am 02:19 AM

java redis

How to parse JSON in Java?

There are three common ways to parse JSON in Java: use Jackson, Gson, or org.json. 1. Jackson is suitable for most projects, with good performance and comprehensive functions, and supports conversion and annotation mapping between objects and JSON strings; 2. Gson is more suitable for Android projects or lightweight needs, and is simple to use but slightly inferior in handling complex structures and high-performance scenarios; 3.org.json is suitable for simple tasks or small scripts, and is not recommended for large projects because of its lack of flexibility and type safety. The choice should be decided based on actual needs.

Jul 11, 2025 am 02:18 AM

java json

What is the Java Memory Model?

Java Memory Model (JMM) is a set of rules to ensure the consistency of concurrent execution of Java programs on different platforms. 1. It improves performance through the division of main memory and working memory, but may lead to variable visibility problems; 2. JMM defines 8 operations to control memory interactions, such as read, load, use, assign, store, write, lock, unlock, and requires pairs to appear to ensure synchronization; 3. The volatile keyword guarantees visibility and orderliness, but does not guarantee atomicity, and is suitable for use in combination with state flags and CAS; 4. The happens-before principle provides a basis for judging memory visibility, including program order, lock, and volatile variables

Jul 11, 2025 am 02:17 AM

What is the difference between map and flatMap in Java Streams?

In Java streams, maps are suitable for one-to-one conversions, while flatMap is used for one-to-many conversions or flattened nested structures. For example, use map to convert a string list to uppercase, and each element generates a result; and flatMap can expand nested lists, such as converting List to single-class, or dealing with Optional values. The key difference is that map converts each element into a new element, while flatMap converts each element into a stream and then merges it into a stream. Common misunderstandings include misuse of maps to cause nested streams or obfuscating return types. At this time, the compiler should use flatMap instead.

Jul 11, 2025 am 02:13 AM

What is the diamond problem in Java?

Thediamondproblemoccurswhenaclassinheritsfromtwoparentclassesthatbothinheritfromthesamegrandparentclass,causingambiguityinmethodresolution.1.Javaavoidsthisbynotallowingmultipleinheritanceofclasses.2.However,Javaallowsimplementingmultipleinterfaceswit

Jul 11, 2025 am 01:51 AM

What is a JWT and how to use it in a Java application?

The use of JWT in Java applications involves generation, parsing and verification of tokens, and its core is implemented through dependency libraries such as auth0/java-jwt. 1. Add Maven dependencies to introduce the java-jwt library; 2. Use the HMAC256 algorithm and key to generate a token containing the topic and declaration; 3. Build a validator to parse and verify the token signature; 4. Extract the declaration from the payload for permission judgment. In actual applications, it is necessary to safely store keys, enable HTTPS transmission, set the token expiration time, and integrate it with SpringSecurity to ensure the security and flexibility of authentication and authorization.

Jul 11, 2025 am 01:45 AM

java jwt

How to produce and consume messages from Apache Kafka with Java?

The key to producing and consuming ApacheKafka messages using Java is to properly configure the Producer and Consumer APIs and understand their basic processes. 1. First add Kafka client dependencies to ensure that the version is compatible with the cluster; 2. When writing producers, configure bootstrap.servers, key.serializer and value.serializer, and create a KafkaProducer instance to send messages, pay attention to closing resources and optional callback processing; 3. When writing consumers, configure group.id, deserializer, etc., use KafkaConsumer to subscribe to topics and loop to pull messages, pay attention to submitting offset

Jul 11, 2025 am 01:43 AM

java kafka

Java multithreading tutorial

The key to Java multi-threading programming is to understand thread creation, synchronization mechanism and resource management. 1. Threads are the basic unit of program execution. They can be created by implementing the Runnable interface or inheriting the Thread class; 2. Synchronized, wait/notify or ReentrantLock are required to control the execution order; 3. Avoid deadlocks, unified resource application order, set timeouts and reduce nested locks; 4. Using thread pools can improve performance. It is recommended that ExecutorService manage fixed, single-thread or cache pools. Mastering these core points can effectively deal with concurrent scenarios.

Jul 11, 2025 am 01:39 AM

Testing Java Code Effectively with JUnit Framework

JUnit is the preferred framework for Java unit testing because of its simplicity, stability and extensive integration. Using JUnit can improve code quality, especially when modifying or extending features. To start writing the first test, you need to: 1. Add dependencies; 2. Create a test class and end with Test; 3. Use the @Test annotation method and write assertions. Practical testing should: cover core logic, maintain independence, use Setup/Teardown, and test exception behavior. Test coverage cannot be ignored, but it is necessary to analyze effective paths in combination with tools such as JaCoCo and connect to CI to ensure continuous integration.

Jul 11, 2025 am 01:25 AM

Exploring New Features Introduced in Java 8

The core new features of Java8 include Lambda expressions, StreamAPI, and default methods. 1. Lambda expressions simplify the implementation of functional interfaces, making the code more concise, but it should be noted that it is only applicable to functional interfaces and should not be too complicated; 2. StreamAPI provides declarative data processing methods to improve collection operation efficiency, but should avoid using them on small amounts of data and reduce side effects; 3. The default method allows interfaces to define methods to implement, enhance backward compatibility, but cannot access class state and need to solve method conflict problems. The rational use of these features can improve code quality and development efficiency.

Jul 11, 2025 am 01:24 AM

java java 8

Handling Null Pointer Exceptions Safely in Java

The key to dealing with null pointer exceptions lies in prevention and reasonable response. 1. Understand the root cause of NullPointerException, such as accessing properties or methods of null objects, obtaining null array length, etc.; 2. Use the Optional class to elegantly process values ??that may be null, such as ofNullable, ifPresent, orElse, etc.; 3. Make good use of conditional judgments and tool classes for defensive programming, such as manually null, using Objects.requireNonNull(), StringUtils.isNotBlank(), etc.; 4. Follow practical suggestions in daily development, such as not assuming that variables have values, clarifying that interface null is legal

Jul 11, 2025 am 01:22 AM

java Null pointer exception

What is Project Reactor and reactive programming in Java?

ReactiveprogramminginJavaisaparadigmforhandlingasynchronousdatastreamsefficiently.Itusesnon-blockingoperationsandbackpressuretomanagehighconcurrencyandreal-timeinteractions.ProjectReactorprovideskeytoolslikeFlux(formultipleitems)andMono(forzerooronei

Jul 11, 2025 am 12:38 AM

reactive programming

Java lambda expressions tutorial

LambdaexpressionsinJavaareinlinefunctionsusedwithfunctionalinterfacestomakecodecleaner.IntroducedinJava8,theyallowtreatingfunctionalityasamethodargument.Theysimplifytaskslikesorting,filtering,andeventhandling.Tousethem,matchthelambdatoafunctionalinte

Jul 11, 2025 am 12:36 AM

java

How to check if a number is prime in Java?

TocheckifanumberisprimeinJava,thecoremethodinvolvestestingdivisibilityuptothesquarerootofthenumber.1.First,handleedgecases:numberslessthanorequalto1arenotprime,2isprime,andevennumbersgreaterthan2arenotprime.2.Usealoopstartingfrom3uptothesquarerootoft

Jul 11, 2025 am 12:32 AM

java prime numbers