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Different return type conversion strategies in Java: Building flexible service layer data mapping

In response to the inconsistent return types of controller and service layer in Java Spring Boot applications, this article explores in-depth how to effectively convert between unrelated object types (such as Resresource and Excel). The article will focus on how to implement custom data mappers, including manual mapping and strategies to leverage existing mapping libraries, aiming to ensure that the service layer always returns the specific types expected by the controller, thereby improving code robustness and maintainability.

Aug 21, 2025 am 02:54 AM

What is the difference between public, private, protected, and default access modifiers in Java?

ThefouraccessmodifiersinJavaarepublic,private,protected,anddefault,eachdefiningdifferentlevelsofvisibility:publicallowsaccessfromanyclass;privaterestrictsaccesstowithinthesameclass;protectedpermitsaccesswithinthesamepackageandbysubclassesinotherpacka

Aug 21, 2025 am 02:29 AM

How to convert a string to an int in Java

To convert a string to int, you should use the Integer.parseInt() method; 1. Use Integer.parseInt(str) to directly return the primitiveint type, such as Stringstr="123"; intnum=Integer.parseInt(str); output 123; 2. Use Integer.valueOf(str) to return the Integer object, but it can be assigned to the int variable through automatic boxing, such as Stringstr="456"; intnum=Integer.valueOf(st

Aug 21, 2025 am 01:12 AM

What is a ByteBuffer in Java?

AByteBufferinJavaisafixed-sizebufferforhandlingbinarydataefficiently,primarilyusedinNIOoperations;itsupportsdirectbytemanipulation,primitivetypeI/O,andofferspositionandlimitcontrolsforreadingandwriting,withtwotypes—heap-basedanddirect—enablinghigh-pe

Aug 21, 2025 am 12:55 AM

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How do you safely convert a String to an integer in Java?

UseInteger.parseInt()withtry-catchtohandleinvalidinputlikenull,emptystrings,ornon-numericcharacters,whichthrowsaNumberFormatException;2.UseInteger.valueOf()toreturnanIntegerobjectinsteadofaprimitive,usefulfornullability;3.Pre-validatewithahelpermetho

Aug 21, 2025 am 12:40 AM

How do you define and throw a custom exception in Java?

DefineacustomexceptionclassbyextendingExceptionforcheckedexceptionsorRuntimeExceptionforuncheckedexceptions,providingconstructorsthatacceptamessageandoptionallyacause.2.Throwtheexceptionusingthethrowkeywordinyourcode,declaringitwiththrowsforcheckedex

Aug 21, 2025 am 12:15 AM

How to understand Java memory model (JMM)?

TheJavaMemoryModel(JMM)defineshowthreadsinteractwithmemory,ensuringvisibility,ordering,andconsistencyofshareddataacrossthreads.2.Withoutsynchronization,visibilityissuesarisebecausethreadsmaycachedataandcompilersorCPUsmayreorderinstructions,leadingtou

Aug 20, 2025 pm 01:36 PM

How to use the Stream API for grouping and partitioning in Java?

UseCollectors.groupingBytocategorizeelementsintoaMapbasedonaclassificationfunction,suchasgroupingPersonobjectsbyage,resultinginamapwherekeysareagesandvaluesarelistsofpersons.2.Refinegroupingresultswithdownstreamcollectors,forexample,extractingonlynam

Aug 20, 2025 pm 01:35 PM

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How to create a sealed class in Java

Java17 and above support sealed classes, and the allowed subclasses are defined through the sealed keyword and permits clause, and each direct subclass must be declared as final, sealed or non-sealed. 1. Use sealed to modify the class, 2. List allowed subclasses through permits, 3. Ensure that each subclass clearly marks its sealed state, and all relevant classes must be in the same module or package. This mechanism provides compile-time inheritance control, improving pattern matching security and domain modeling accuracy. Summary: Java17 can achieve controlled inheritance through the sealed permits subclass modifier.

Aug 20, 2025 pm 01:32 PM

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Debugging 'Teen Talk' program: Solve infinite loop problem

This article aims to help readers debug a Java program called "Teen Talk" that is designed to simulate how teenagers talk, adding "like" after each space. The article analyzes the causes of infinite loops in the program and provides modified code examples to ensure that the program runs correctly and outputs the expected results.

Aug 20, 2025 pm 01:12 PM

Java multithreaded task scheduling: Efficiently handle shared list tasks with ExecutorService

This article explores in-depth how to efficiently and safely assign and execute tasks from shared tasks lists in a Java multithreaded environment. In view of the complexity of manually managing task distribution, the article focuses on recommending and elaborating on ExecutorService as a core solution. It automates task scheduling through internal mechanisms to ensure that thread resources are fully utilized. The article provides detailed Java code examples and discusses BlockingQueue as the underlying implementation principle, while highlighting key considerations when using concurrency tools, aiming to help developers build robust concurrent applications.

Aug 20, 2025 pm 01:06 PM

What is the lifecycle of a thread in Java?

The life cycle of a Java thread includes six states: New, Runnable, Blocked, Waiting, TimedWaiting and Terminated; when creating a thread through Thread or Runnable, it is in the New state, and after calling start(), it becomes Runnable, waiting for CPU scheduling to execute. If you try to obtain a synchronization lock, it enters the Blocked state. Calling wait() or join() and other methods will enter the Waiting or TimedWaiting state, waiting for a specific event or timeout to resume, the run() method will be executed or terminated abnormally and cannot

Aug 20, 2025 pm 01:05 PM

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What is the purpose of the static keyword in Java?

ThestatickeywordinJavaisusedtocreateclass-levelmembersthatbelongtotheclassratherthananyinstance,allowingthemtobeaccessedwithoutcreatinganobject;staticvariablesaresharedamongallinstancesandinitializedwhentheclassisloaded,staticmethodscanonlyaccessstat

Aug 20, 2025 pm 12:58 PM

Practice of service layer return type conversion and data model mapping in Java

This article discusses the type conversion problem caused by mismatch between the service layer and the controller layer in Java applications. In the scenario where the service layer returns an Object type and needs to be converted to a specific business object (such as Resresource) at the controller layer, the article details how to implement smooth conversion between different data structures (such as Excel and Resresource) through a custom data mapper (Mapper), thereby ensuring type safety and code maintainability.

Aug 20, 2025 pm 12:57 PM