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Technical Articles

Java

javaTutorial

How to write unit tests in Java?

To write Java unit tests, you must first introduce JUnit5 in the project, add junit-jupiter dependency in pom.xml, add testImplementation'org.junit.jupiter:junit-jupiter:5.9.3' for Gradle project, and place the test class in the src/test/java directory; then create a test class, use @Test annotation to mark the test method, and verify behavior through assertions such as assertEquals and assertThrows, such as testing the add and divide methods of the Calculator class; use @Before

Aug 14, 2025 pm 07:28 PM

java unit test

How do you check if a number is prime in Java?

To determine whether a number is a prime number, the answer is: 1. If the number is less than or equal to 1, it is not a prime number; 2. If it is 2, it is a prime number; 3. If it is an even number and greater than 2, it is not a prime number; 4. Check whether the odd number from 3 to its square root can be divided. If it exists, it is not a prime number, otherwise it is a prime number. This method uses integer operation to avoid floating point errors by handling boundary conditions, excluding even numbers and only checking odd numbers, and using integer operations to avoid floating point errors, thus efficiently judging prime numbers. It is suitable for general scenarios and is fully implemented as shown in the above Java code.

Aug 14, 2025 pm 07:12 PM

Robustness in Java parallel tasks: Independent exception handling and result collection strategies

This article discusses how to ensure that exceptions of a single task do not interrupt the entire processing flow when executing parallel method calls in Java. We will introduce a robust strategy to use CompletableFuture to perform each task independently and to catch and record exceptions inside the task rather than propagate immediately. In this way, even if some tasks fail, all parallel tasks can continue to be completed and ultimately aggregate the results and error information of all tasks, thereby improving the resilience and usability of the system.

Aug 14, 2025 pm 07:06 PM

How to use Optional to avoid NullPointerException in Java

Optional is used to avoid NullPointerException in Java. The correct usage methods include: 1. Use Optional.of, Optional.ofNullable or Optional.empty to return a value that may be empty; 2. Use isPresent to combine get or more recommended ifPresent to handle the existence of the value; 3. Use orElse or delayed calculations to provide the default value; 4. Use map and flatMap to safely convert the value to avoid nested Optional; 5. Use orElseThrow to throw exceptions when the value is missing; 6. Avoid using Optional for

Aug 14, 2025 pm 06:33 PM

Efficiently manage and execute a large number of Linux commands in Java

This article discusses the strategies and challenges of large-scale execution of Linux commands (such as socat) in Java applications. We will analyze in detail the key links such as concurrent execution, I/O stream processing, resource management, etc., and provide practical methods based on ProcessBuilder and thread pools, aiming to help developers achieve high-performance and highly concurrent command execution, and effectively avoid common performance bottlenecks, such as high load and system lag.

Aug 14, 2025 pm 06:33 PM

How to use JSPs in Java

JSP(JavaServerPages)isaserver-sidetechnologythatembedsJavacodeintoHTMLusingspecialtagslikeandtogeneratedynamiccontent.2.TouseJSPs,setupaJavawebprojectwiththeproperstructure,includingawebappdirectoryandWEB-INFfolder,anddeployitonaservletcontainerlikeA

Aug 14, 2025 pm 06:32 PM

Manage Google Calendar Events with Service Accounts: Solving 403 Permission Issues and Best Practices

This article explores in-depth how to use Google Service Account and its Domain-Wide Delegation (DWD) to manage Google Calendar events, especially to resolve common 403 permission errors. We will explain in detail the difference between service accounts and user authorization, provide Java code examples, and clarify DWD configuration steps, common pitfalls, and how to ensure that service accounts safely and effectively represent the user's operating calendar without directly accessing user credentials.

Aug 14, 2025 pm 06:30 PM

Efficient comparison of collection elements in Java: Tutorial for finding missing items using Set

This tutorial is designed to solve the problem of comparing two collections (such as shopping lists vs inventory lists) in Java to determine if there are missing items. The article will analyze the limitations of traditional linear search methods and focus on how to optimize this process by leveraging the efficient search characteristics of Set data structures (average O(1) time complexity). With specific code examples, readers will learn how to correctly compare collection elements and effectively identify and report all missing items, thereby improving program performance and readability.

Aug 14, 2025 pm 06:24 PM

Guide to Solving SLF4J Provider-free Warnings in Spring Boot Integration Tests

This article aims to solve the problem that the "No providers were found" warning in the Gradle integrated test environment of Spring Boot applications, causing the log to be unable to output. By analyzing the binding mechanism and version compatibility of SLF4J, we found that this is usually caused by the mismatch or conflict between the SLF4J API and the log implementation binding version in the classpath. The article provides a specific Gradle dependency solution and discusses relevant considerations to ensure that the logging system works properly during different testing stages.

Aug 14, 2025 pm 06:21 PM

Spark: Remove columns from beans before partition writing

This document describes how to dynamically remove unwanted columns based on different partitioning policies when writing Bean objects to partitions using Spark. By using the select method before writing, you can flexibly select the columns that need to be written, avoiding problems caused by mismatch in data formats and simplifying code maintenance.

Aug 14, 2025 pm 06:18 PM

How to sort an array in Java?

Use Arrays.sort() to sort the array, 1. Sort(arr) in ascending order for the basic types; 2. Sort(arr,comparator) for objects or custom sorting, use Arrays.sort(arr,comparator), such as Comparator.reverseOrder() or Comparator.comparing(); 3. You can specify the sorting range Arrays.sort(arr, fromIndex, toIndex); 4. The basic types do not support Comparator, and you need to use a wrapper class to implement custom sorting such as descending order. The final result is to modify the ascending order of the original array or specify the order.

Aug 14, 2025 pm 06:14 PM

DynamoDB's massive data efficient query strategy

Efficiently obtaining massive amounts of data from DynamoDB in the Spring Boot REST API is a challenge, especially to avoid loading all data into memory. DynamoDB returns up to 1MB of data in a single request, so a paging mechanism is required to process large amounts of data. Scan operations on large data sets should be avoided because it is not scalable and expensive, and it is recommended to revisit business requirements or consider database solutions that are more suitable for analytical queries.

Aug 14, 2025 pm 06:06 PM

What are terminal operations in Java Streams?

TerminaloperationsinJavaStreamstriggertheprocessingofthestreamandproducearesultorsideeffect,afterwhichthestreamisconsumedandcannotbereused;commontypesincludereductionoperationslikecollect,reduce,andcount,matchingoperationssuchasanyMatch,allMatch,andn

Aug 14, 2025 pm 05:59 PM

What is the difference between checked and unchecked exceptions in Java?

Checkedexceptionsmustbehandledordeclaredandareusedforrecoverableconditions,whileuncheckedexceptionsarenotenforcedbythecompilerandtypicallyindicateprogrammingerrors;specifically,checkedexceptionsextendException(butnotRuntimeException),areverifiedatcom

Aug 14, 2025 pm 05:44 PM