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How to make an asynchronous POST request with HttpClient in Java

To use the HttpClient of Java11 to send an asynchronous POST request, you need to follow the following steps: 1. Create an HttpClient instance, such as HttpClientclient=HttpClient.newHttpClient(); 2. Build an HttpRequest containing URI, header information and request body, such as using POST (HttpRequest.BodyPublishers.ofString(json)) and set Content-Type; 3. Call client.sendAsync(request,HttpResponse.BodyHandle

Aug 08, 2025 am 11:58 AM

How to calculate a factorial in Java?

TocalculateafactorialinJava,usetheiterativeapproachforbetterperformancebyinitializingresultto1andmultiplyingitbyeachintegerfrom1toninaloop.2.Usetherecursiveapproachforclarity,wherethefunctioncallsitselfwithn*factorialRecursive(n-1)andbasecasesreturn1

Aug 08, 2025 am 10:46 AM

How to create and start a thread in Java

TocreateandstartathreadinJava,youcanextendtheThreadclassandoverrideitsrun()method,thencallstart()tobeginexecution;2.Alternatively,implementtheRunnableinterface,passaninstancetoaThreadconstructor,andcallstart();3.PreferimplementingRunnableorusinglambd

Aug 08, 2025 am 10:37 AM

Implementing CQRS and Event Sourcing in a Java Application

CQRS and event traceability can significantly improve the scalability, maintainability and auditing capabilities of Java applications by separating read and write models and storing state changes in event-driven mode; 1. Understand that CQRS separates commands from queries, and event traceability rebuilds state through event streams; 2. Use SpringBoot to integrate AxonFramework 4.6.0 and add H2 and JPA dependencies; 3. Define the aggregate root containing the commands, events and @Aggregate annotation of @TargetAggregateIdentifier; 4. Update the JPA read model in the projection component through @EventHandler; 5. Expose the REST endpoints of commands and queries respectively, and use Comma

Aug 08, 2025 am 10:18 AM

cqrs

Java: How to call non-static methods of an existing class without creating a new object? (Especially for GUI event handling)

This article explains in detail how to call a non-static method of an existing class in Java without creating a new object instance. Especially for graphical user interface (GUI) development, a common problem encountered when an event listener needs to interact with an existing JFrame instance. The article will use instance code to demonstrate how to obtain and operate target objects safely and effectively through constructor injection or using the Inner Class mechanism, avoid creating unnecessary duplicate instances, and ensure the correctness of program logic and effective utilization of resources.

Aug 08, 2025 am 10:12 AM

A Guide to Java Native Image (JNI) and Interoperability

JNIisusedforJavatointeractwithnativeC/C code,enablingintegrationwithexistinglibrariesorsystemAPIs;1.WriteJavaclasswithnativemethodsandloadlibrary;2.Generateheaderwithjavac-h;3.ImplementCfunctionusingJNIconventions;4.Compiletosharedlibrary;5.RunonJVM

Aug 08, 2025 am 10:11 AM

The strategy and implementation of generating gapless serial numbers for multiple application instances

This article discusses the challenges and solutions for generating gapless serial numbers in a multi-application instance environment. By introducing an independent counter table and combining the pessimistic write-lock mechanism, it is ensured that in concurrent operations and transaction rollback scenarios, the serial number can be strictly incremented without any jumps or repetitions. The article provides Java/JPA-based implementation examples and explains in detail how it works and key considerations.

Aug 08, 2025 am 10:06 AM

How to execute an external command in Java?

Use Runtime.exec() to execute external commands, but it is necessary to note that spaces and special characters should be passed into a string array; 2. It is recommended to use ProcessBuilder because it is more flexible and is convenient for setting working directories, environment variables and complex parameters; 3. The input stream and error stream must be read to avoid deadlocks; 4. Process.waitFor() should be called to wait for the process to end; 5. The command has platform dependencies, such as Windows uses dir and Unix uses ls; 6. The error output can be captured through getErrorStream(), or the error stream can be merged into the output stream with redirectErrorStream(true); in summary, in addition to maintaining old code, priority should be given

Aug 08, 2025 am 10:04 AM

java external command

Java type conversion: Deeply understand the special rules of constant expressions and assignment conversion

This article discusses the assignment conversion rules of basic data types in Java in detail, especially the special treatment for constant expressions. When a constant expression of type int is assigned to byte, short, or char, the compiler allows implicit narrowing conversion if the value is within the target type range. However, for long-type values, even constants, there is no special rule, and the assignment to int still requires explicit conversion. The article will also analyze the impact of operator priority and numerical enhancement on expression types and explain the design intention of this rule.

Aug 08, 2025 am 10:03 AM

Strategies and practices for calling non-static methods of existing objects in Java

This article aims to solve how to call a non-static method of another existing class instance from one class in Java instead of creating a new object. The article will explore in-depth strategies for implementing cross-class communication by passing object references and utilizing internal classes and other mechanisms, and provide specific code examples to help developers avoid common problems such as accidentally creating new UI components, and ensure that operations act on the correct and existing object instances.

Aug 08, 2025 am 09:57 AM

The solution to the jdk.dio package cannot be found when using OpenJDK 18

This article describes why the jdk.dio.mmio package cannot be found when using OpenJDK 18, which belongs to the Java ME environment rather than Java SE. The article explains the difference between Java ME and Java SE, and points out that there is no package in Java SE that is directly equivalent to jdk.dio.mmio. At the same time, the article also provides information about the DIO code base on java.net and reminds that the code base may not correspond to the Java ME version of javadocs.

Aug 08, 2025 am 09:54 AM

How to find the most expensive and cheapest objects in Java arrays

This article details the correct way to traverse an array of objects in Java and find the most expensive and cheapest instances of a specific type, such as UAV. By distinguishing and independently tracking the actual price of an object and its index in the array, and properly initializing the comparison variables, common logical errors can be avoided, ensuring that the maximum and minimum values of objects that meet the conditions are accurately identified.

Aug 08, 2025 am 09:45 AM

The solution to the jdk.dio package cannot be found when using Java SE

This article aims to solve the problem of "package not found" when trying to import jdk.dio.mmio packages using Java SE (OpenJDK). Help developers understand the problem and find the right solution by explaining the origin and nature of the jdk.dio.mmio package and providing directions to explore alternatives.

Aug 08, 2025 am 09:42 AM

Solve the issue of permission invalidation after Android PDFView restart

This article provides a detailed solution to the problem that SecurityException permission error occurs after the device restarts when using the PDFView library to open a PDF file in Android applications. The main reason is that URI permissions are lost after restarting. The persistent URI permissions are obtained through takePersistableUriPermissions() method to ensure that the application can still access PDF files after restarting, thereby avoiding permission issues.

Aug 08, 2025 am 09:39 AM