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Technical Articles

Java

javaTutorial

Check if Row Schema contains specified fields in Apache Spark

This article details how to efficiently check whether the StructType schema of a Row object contains a specific field name in Apache Spark. We will explore two main public methods: using the exists method to combine predicate functions for flexible matching, and using the getFieldIndex method to determine whether a field exists and obtain its index, and provide corresponding code examples to help developers accurately verify the data structure.

Aug 25, 2025 pm 12:57 PM

Minimize the time required to complete tasks: a scan line-based solution

This article describes a problem of using a scan line algorithm to solve the problem of minimizing the time it takes to complete a given task. Tasks are defined by the start time, the end time, and the required time length. The core idea of ??the algorithm is to sort the start and end time points of the task, then simulate the time elapse, and maintain an active task stack, thereby calculating the minimum time required to complete all tasks.

Aug 25, 2025 pm 12:45 PM

How to create a custom exception in Java

Decidewhethertheexceptionshouldbechecked(extendException)orunchecked(extendRuntimeException)basedonrecoverability;2.Createaclasswithstandardconstructors(default,message,cause,andmessagewithcause)toensureproperexceptionhandling;3.Usethecustomexception

Aug 25, 2025 pm 12:34 PM

Optimize AWS Java SDK EC2 API calls: Use an asynchronous client to avoid connection resets

When calling EC2 services (such as describeImages) using the AWS Java SDK, you sometimes encounter the "Unable to execute HTTP request: Connection reset" error, while S3 and other services are called normally. This article will explore the root cause of this problem in depth and provide a solution: By replacing the synchronous client AmazonEC2ClientBuilder with the asynchronous client AmazonEC2AsyncClientBuilder, it can effectively solve the problem of request failure due to network or connection stability, ensuring the smooth execution of AWS service calls.

Aug 25, 2025 pm 12:27 PM

what is reflection in java

ReflectioninJavaenablesprogramstoexamineandmanipulateclasses,fields,methods,andconstructorsatruntime,providedbythejava.lang.reflectpackageandtheClassclass;itworksbyaccessingmetadatastoredinClassobjectswhenaclassisloaded,allowingdynamicinstantiation,m

Aug 25, 2025 pm 12:16 PM

Java Tutorial: Aggregate the values ??of duplicate elements in List using Map

This article describes how to efficiently aggregate the values ??of elements with duplicate keys in List using Map data structures and Stream APIs in Java. By converting List to Map and using the compute method or toMap collector, it is easy to accumulate attributes such as Amount and Quantity of the repeating elements to finally obtain the aggregated result.

Aug 25, 2025 pm 12:09 PM

Aggregate the values ??of duplicate elements in List using Java Map

This article describes how to use Java Map structure to effectively aggregate numeric values ??of elements of the same type in a List, such as Amount and Quantity. By converting List to Map and leveraging the compute method or the toMap operation of the Stream API, manual loops and comparisons can be avoided, simplifying code and increasing efficiency. This tutorial provides detailed code examples showing how to create, update, and merge data in a map to finally get aggregated results.

Aug 25, 2025 am 11:57 AM

How to rearrange words in strings based on embedded numbers

This tutorial will explore how to reorder words based on numbers embedded in strings. We will take "my1kiran4name2is3" as an example, and the target output is "my name is kiran". The article will detail a solution based on Java regular expressions (Lookarounds) and Stream API, parse how it works, discuss the tradeoff between simplicity and readability of the approach, and provide an optimization that ensures correct sorting.

Aug 25, 2025 am 11:54 AM

Calculate the difference between days, hours, minutes and seconds between two dates and times in Java

This article aims to guide Java developers on how to calculate the difference in days, hours, minutes and seconds between a given date and time (for example: "Wednesday 02-October-2022 11:51:1 PM") and the current time. The article will provide detailed descriptions on how to parse date and time strings using DateTimeFormatter, how to process time zone information, and how to calculate time difference using Duration class, and provide corresponding sample code.

Aug 25, 2025 am 11:51 AM

Use JMockit to auto-assemble dependencies and inject Mock objects

This article describes how to use the JMockit framework to automatically assemble dependencies in test classes and inject Mock objects into the class to be tested. The combination of @Tested and @Injectable annotations allows you to easily create instances with Mock dependencies, simplifying the writing process of unit tests and ensuring the validity and reliability of tests. The article provides detailed code examples and precautions to help readers quickly master the skills of using JMockit.

Aug 25, 2025 am 11:45 AM

Practice of different data types conversion and mapping between Java service layer and controller

This article discusses how to effectively convert and map when the data type returned by the service layer is inconsistent with the type expected by the controller in Java applications. This highlights the implementation method of custom object mappers and considerations when designing the type level. Through instance code, the strategy of converting irrelevant objects (such as Excel data model) into target response objects (such as Resresource) is explained, and the importance of unified return types at the service layer, avoiding the use of Objects, and clear API contracts is emphasized, aiming to improve the maintainability and robustness of the code.

Aug 25, 2025 am 11:36 AM

Spring Boot Application Configuration Center Client Integration Guide

This article aims to guide developers to configure Spring Boot applications as a configuration center client to enable them to dynamically obtain configuration from a remote configuration server. The article will introduce in detail how to add necessary dependencies, configure client attributes, and solve common problems of configuration failure, helping readers quickly build a reliable configuration management solution.

Aug 25, 2025 am 11:30 AM

Inject static configuration values ??into GWT client code using the Gin module

This article describes how to inject static configuration values ??into GWT client code to avoid problems caused by using Guice directly on the client. By using the Gin module, we can effectively bind configuration values ??into client code, enabling clearer, maintainable GWT applications. This article will provide detailed descriptions on how to use the Gin module and provide sample code to help you understand and apply this approach.

Aug 25, 2025 am 11:24 AM

How to cache introspective requests in Spring Security

This document aims to guide developers how to cache OAuth2 introspective requests in Spring Security to improve the stability and performance of resource servers and reduce dependence on authenticated servers. By customizing the OpaqueTokenIntrospector and utilizing the caching mechanism, it can effectively reduce 401 errors and improve user experience. This article will provide detailed code examples and step instructions to help you easily achieve caching of introspective requests.

Aug 25, 2025 am 11:21 AM