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How to create JSON from Java objects using Jackson

To convert Java objects to JSON using Jackson, you must use the ObjectMapper class. 1. Add Jackson dependency: Add Jackson-databind dependency in Maven, or add corresponding libraries in Gradle. 2. Create a Java class: Define a POJO that contains fields, constructors, getters and setters, such as the User class. 3. Create an ObjectMapper instance: Initialize the ObjectMapper object in the code. 4. Convert to JSON: Call writeValueAsString() method to serialize Java objects into JSON strings. 5. Optional formatting input

Sep 07, 2025 am 01:47 AM

How to use a for-each loop in Java

Thefor-eachloopinJavaisanenhancedforloopthatsimplifiesiterationoverarraysorcollections.1.Itusesthesyntax"for(typevariable:arrayOrCollection)"toaccesseachelementdirectly.2.Iteliminatesmanualindexmanagement,reducingerrorslikeout-of-boundsexce

Sep 07, 2025 am 01:35 AM

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What is the difference between a JAR and a WAR file in Java?

AJARfileisusedforgeneral-purposeJavapackagingsuchaslibrariesorstandaloneapplications,whileaWARfileisspecificallydesignedforwebapplicationsdeployedonaservletcontainer;JARfileshaveaflexiblestructureandcanbeexecuteddirectlyiftheycontainamainclass,wherea

Sep 07, 2025 am 01:20 AM

java JAR WAR

How to find an element in an ArrayList in Java

To find elements in ArrayList, choose different methods according to your needs: 1. Use contains() to check whether the element exists, return true or false; 2. Use indexOf() to get the index of the first occurrence of the element, return -1, or use lastIndexOf() to get the index of the last occurrence of the element; 3. For conditional searches, you can use the for-each loop or Java8's StreamAPI, such as filter().findFirst() to find the first match, or collect() to collect all elements that meet the conditions; 4. For custom objects such as Person class, equals() and hashCo need to be rewrite

Sep 07, 2025 am 12:42 AM

Understanding the Java Memory Model for Concurrent Programming

TheJavaMemoryModel(JMM)definesrulesformemoryvisibilityandorderinginmultithreadedprograms.2.Thehappens-beforerelationshipensuresthatactionsinonethreadarevisibletoanother,establishedthroughprogramorder,lockacquisition/release,volatilevariables,threadst

Sep 07, 2025 am 12:20 AM

Android Tutorial: Handling the Passing of Toast and Context in Universal Tool Class

This article aims to solve the Context delivery problem encountered when calling Toast messages in non-Activity classes (such as project management classes) in Android development. By elaborating on the importance of Context in UI operations in detail and providing a solution to receive Context parameters using static methods, we ensure that developers can efficiently and safely reuse Toast functions in any activity and avoid duplicate code.

Sep 06, 2025 am 11:42 AM

Elasticsearch exists Query Field Name Case Sensitivity Processing Guide

When checking whether a field exists, the field name is strictly case sensitive. At present, there is no built-in mechanism that can directly implement ignoring case query of field names. This means that "color" and "COLOR" will be treated as two different fields. The core of solving this problem lies in the standardization of field naming during the data model design phase, or preprocessing of field names at the application layer.

Sep 06, 2025 am 11:36 AM

Solve the problem of EJB and Web Service deployment and WSDL access in WildFly

This article aims to resolve common class loading failures (NoClassDefFoundError) and Web service WSDL access errors when deploying EJB and Web services in WildFly application servers. The tutorial will analyze the Maven dependency configuration and WildFly class loading mechanism in detail, and provide a solution to explicitly declare module dependencies through jboss-deployment-structure.xml, and at the same time correct the URL configuration of the Web service endpoint to ensure successful deployment and correct access of the application.

Sep 06, 2025 am 11:30 AM

Solve StackOverflowError caused by fast sorting of large data volumes

This article aims to solve the StackOverflowError that may occur when using a quick sort algorithm to process large arrays of data. By analyzing the reasons for the excessive depth of recursive call, and providing an optimized quick sort implementation, this implementation optimizes the spatial complexity to O(log n) by controlling the recursive depth, thereby avoiding stack overflow problems while maintaining the efficiency of quick sorting. This article also provides code examples for readers to understand and apply.

Sep 06, 2025 am 11:12 AM

Using Spring Boot to build arithmetic operation POST API tutorial on JSON format

This tutorial will guide you how to use the Spring Boot framework to create a POST API endpoint that receives requests from JSON format. The API can perform arithmetic operations on two integers based on the operation type (add, subtract, and multiply) in the request, and returns a JSON response containing the operation result and the specified username. The article will provide detailed descriptions on how to define data transfer objects (DTOs), enumeration types, implement business logic services, and build REST controllers, and provide complete sample code and test methods.

Sep 06, 2025 am 11:09 AM

Kotlin implements an ordered linked list to find intersections and delete elements

This article describes how to implement a function in Kotlin that receives two bidirectional loops list1 and list2, as well as a comparator cmp. The function is to find the intersection of two linked lists and delete the intersection element from the original linked list. Finally, a new linked list is returned, which contains the intersection elements of the two input linked lists, without duplicate elements, and retains the original order of the elements.

Sep 06, 2025 am 10:54 AM

Output format requirements: Best practices for using this keyword in Java

This article explores how to effectively pass this keyword to Supplier in a Java 8 environment, especially in asynchronous programming scenarios such as CompletableFuture. The article analyzes the different ways of using Lambda expressions and method references and discusses their potential performance impacts, aiming to help developers choose the best solution for their needs, avoid unnecessary resource consumption, and write more efficient and concise code.

Sep 06, 2025 am 10:27 AM

Solution to empty @Autowired field in Spring Boot integration test

This article aims to solve the problem of null pointer exceptions in Spring Boot integration tests when using @Autowired annotation for Repository fields. Typically, this indicates that the test is not running in the Spring context, resulting in dependency injection failure. This article provides detailed troubleshooting and solutions to ensure that integration tests run correctly in the Spring context and successfully inject the required dependencies.

Sep 06, 2025 am 10:24 AM

Activity life cycle management when optimizing screen direction switching in Android applications

This article aims to solve the problem of screen orientation changes in Android applications causing Activity reset, especially when using components such as Azure Maps that need to remain state. By modifying the tags in the AndroidManifest.xml file and adding the android:configChanges="orientation|keyboardHidden|screenSize" attribute, developers can block the default reconstruction behavior of the Activity and instead trigger the onConfigurationChanged() method. This strategy effectively avoids UI state loss and data overloading, thus

Sep 06, 2025 am 10:21 AM