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How to format a double to two decimal places in Java?

ToformatadoubletotwodecimalplacesinJava,youcanuseSystem.out.printfforquickconsoleoutput,String.formattostoretheresultasastring,orDecimalFormatformoreadvancedandcustomizableformatting.①System.out.printfisidealforsimpleprinting,usingtheformatstring&quo

Jul 20, 2025 am 02:00 AM

Applying Clean Architecture Principles in Java

CleanarchitectureinJavaenhancesmaintainability,testability,andscalabilitybyseparatingconcernsthroughlayereddesign.Thestructureincludesentities(domainlayer),usecases(applicationlogic),interfacesandadapters(input/outputhandling),andframeworks/tools(out

Jul 20, 2025 am 01:50 AM

java Architecture

How to find the longest common subsequence of two strings in Java?

Finding the longest common subsequence (LCS) of two strings is usually implemented in Java using dynamic programming. 1. Create a two-dimensional array dp of (m 1)x(n 1), where dpi represents the longest common subsequence length of text1[0..i-1] and text2[0..j-1]; 2. State transition: If text1[i-1]==text2[j-1], then dpi=dpi-1 1, otherwise dpi=max(dpi-1,dpi); 3. After filling the entire array, dpm is the result; 4. Optional optimization is to use one-dimensional array to compress space, suitable for processing large strings. Code time complexity O(mn) and space complexity O(mn), suitable for most scenarios.

Jul 20, 2025 am 01:33 AM

how to read user input from console in java using scanner

The most common way to read Java console user input is to use the Scanner class. 1. You need to import the java.util.Scanner package first and create an object through Scannerscanner=newScanner(System.in); 2. Use next(), nextLine(), nextInt(), nextDouble() and other methods to read different types of data. Note that nextLine() needs to be added after nextInt() to avoid line breaks, and next() cannot read content with spaces; 3. After using it, it is recommended to call scanner.close() to close the resource, but it is necessary to note that it cannot be re-returned after closing.

Jul 20, 2025 am 01:20 AM

Java Asynchronous Programming with CompletableFuture

Asynchronous programming of Java can be implemented through CompletableFuture, and its core lies in encapsulating asynchronous tasks, combining operations and exception handling. 1. Create asynchronous tasks by using supplyAsync or runAsync, or you can manually call complete() to complete the task in advance; 2. Methods of combining multiple tasks include thenApply (convert result), thenAccept (consumption result), thenRun (execute task), thenCompose (consolidation Future) and thenCombine (merge result); 3. Exception handling mechanisms include exceptionally (providing default value), handle (unified processing

Jul 20, 2025 am 01:16 AM

Java Security for File Upload Vulnerabilities

Preventing file upload vulnerabilities requires four aspects. 1. Strictly limit file types, use the whitelist mechanism and verify the real MIME type, and even read the file header judgment; 2. The upload path is separated from the access path, stored in a non-Web directory and controlled access through the intermediate layer, and generated a unique file name using UUID; 3. Prevent path traversal attacks, standardize the paths, and use Java's Paths.get() to combine the whitelist directory to build a secure path; 4. Limit file size and concurrency number, set the maximum size (such as 10MB) on the front and back ends, configure framework parameters and control the number of files uploaded in a single time.

Jul 20, 2025 am 01:15 AM

Java Security Auditing and Compliance

To avoid security vulnerabilities, it is recommended to regularly check and adopt LTS version; 2. Scan and manage known vulnerabilities in third-party dependency libraries, integrate automated detection tools; 3. Properly enable SecurityManager according to the deployment environment and customize permission policies to avoid hard coding of sensitive information; 4. Strengthen logging and access control, implement RBAC and MFA, and ensure log security and compliance retention. These audit points help improve the security and compliance of Java applications.

Jul 20, 2025 am 01:08 AM

How to convert a Date to a String in Java?

There are two core methods for converting Date to String in Java: 1. Use SimpleDateFormat (suitable for Java7 and below), formatting by defining format strings such as "yyyy-MM-ddHH:mm:ss", but be careful when it is thread-safe. Multi-threaded environments should be used with caution, and time zones can be specified through setTimeZone; 2. Use DateTimeFormatter introduced by Java8, which is recommended for new projects, thread-safe and supports more powerful time APIs, such as LocalDateTime and ZonedDateTime, and can be combined with localized format ISO_DA

Jul 20, 2025 am 01:03 AM

Advanced Java Debugging Techniques and Tools

Advanced Java debugging techniques include remote debugging, JFR performance analysis, MAT memory leak detection, and Arthas online diagnosis. Remote debugging requires attention to port opening and performance impact, and dynamic connections can be used in additional modes; enable JFR and cooperate with JMC to analyze threads, GC and method hotspot paths, which are suitable for low-overhead monitoring in production environments; load heap dump files through MAT to view DominatorTree, Histogram and LeakSuspectsReport to locate memory leaks; use Arthas' trace, watch, thread and jad commands to achieve intrusive runtime diagnosis, and improve problem-solving efficiency.

Jul 20, 2025 am 01:00 AM

Building High-Throughput Java Batch Processing Jobs

To build high-throughput Java batch jobs, the key is to read data paging, set batch size reasonably, use thread pools to process in parallel, write data in batches, control transaction granularity, and design a complete exception handling mechanism. Specifically include: 1. Use paging or cursor to read data to avoid OOM; 2. Adjust the appropriate batch size through test to balance I/O and memory pressure; 3. Use ExecutorService for parallel processing and reasonably configure multiple thread pools; 4. Use addBatch() and executeBatch() to achieve efficient batch writing; 5. Submit transactions once per batch to improve performance; 6. Process each batch independently and support failed retry and logging to ensure stability and ability

Jul 20, 2025 am 12:35 AM

Understanding Java Volatile Keyword Semantics

The volatile keyword solves variable visibility and directive reordering problems in Java multithreading. 1. It ensures that all threads can be seen immediately after the variable is modified, and avoids threads from using cached old values; 2. It prevents the compiler and processor from reordering the operations involving volatile variables to ensure the order of operations; 3. It is suitable for scenarios where there is no atomicity, such as status flags, one-time safe release, independent variable assignment, etc.; 4. Unlike synchronized, the volatile lock-free mechanism does not guarantee the atomicity of composite operations, but is lighter and more efficient.

Jul 19, 2025 am 04:34 AM

Securing Java Microservices with OAuth2 and JWT

OAuth2 is responsible for authorization, and JWT is used to transmit information securely. The four roles of OAuth2 include resource owner, client, authentication server and resource server. The common process is the authorization code mode. After the user logs in, the client uses the code to exchange it for the token, and then uses the token to access the resources. JWT includes three parts: header, load and signature. The microservice confirms identity and resolves permission information by verifying the signature. SpringBoot integration uses the OAuth2ResourceServer module to configure issuer-uri and jwk-set-uri, and can customize the permission parser to extract the authorities. Notes include reasonable setting of token expiration time and security

Jul 19, 2025 am 03:59 AM

what is the 'final' keyword in java

In Java, the final keyword is used to restrict the modification of variables, methods, and classes to enhance code security and predictability. ① Variables declared as final cannot be changed once assigned, and are often used to define constants; ② Methods marked as final cannot be rewritten by subclasses to ensure that the logic is not changed; ③ Final class cannot be inherited to ensure that the implementation is not modified; ④ Uninitialized final variables (blank finals) can be assigned once in the constructor to improve flexibility and maintain invariance.

Jul 19, 2025 am 03:58 AM

Java Persistence API (JPA) Advanced Mappings

This article introduces four advanced mapping methods of JPA. 1. Bidirectional association specifies the relationship maintainer through mappedBy to achieve mutual access between User and Address; 2. Many-to-many association uses @ManyToMany and @JoinTable to manage intermediate tables, or manually create entity classes to expand intermediate table functions; 3. Embed objects use @Embeddable and @Embedded to embed Address into the Order table, supporting compound primary key design; 4. The inheritance structure uses SINGLE_TABLE, JOINED, and TABLE_PER_CLASS policies to map Employee subclasses, and select appropriate solutions according to query needs.

Jul 19, 2025 am 03:55 AM

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