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Technical Articles

Java

javaTutorial

Spark: Remove columns from beans before writing to partition

This article describes how to dynamically remove unwanted columns according to different partition requirements when writing Bean objects to partitions using Spark. By using the beanDataset.select() method to select the columns you want before writing, you can flexibly handle various partition combinations, avoiding the creation of multiple bean classes, simplifying code and increasing efficiency. This article will provide specific code examples and discuss related precautions.

Aug 20, 2025 am 11:06 AM

Spring Boot's strategy and practices for handling non-UTF-8 request encoding

When Spring Boot applications need to be compatible with HTTP requests from traditional systems and adopt non-UTF-8 encoding (such as Windows-1252), garbled characters often occur. This article deeply analyzes the root causes of such problems, points out common test misunderstandings, and provides correct client simulation methods, emphasizing the importance of ensuring that the actual encoding of the request body is consistent with the Content-Type header declaration, so as to ensure that Spring Boot can correctly parse requests with different encodings.

Aug 20, 2025 am 11:00 AM

How to memory-map a file in Java?

Memory mapped files are implemented in Java through FileChannel's map() method. The specific steps are: 1. Use RandomAccessFile or FileInputStream to get FileChannel; 2. Call FileChannel's map() method, specify the mapping mode (such as READ_WRITE), the starting offset and size, and return the MappedByteBuffer; 3. Read and write operations through MappedByteBuffer, and the data will be mapped to virtual memory and may be written back to disk. This method is suitable for high-performance random access scenarios, but it is necessary to pay attention to resource release dependent on GC and 32-bit JVM address space

Aug 20, 2025 am 10:48 AM

java 文件映射

How do you reverse a string in Java?

Using StringBuilder.reverse() is the easiest and efficient method, suitable for most cases; 2. Using a loop to invert character by character can provide greater control; 3. Using double pointer swap to reduce memory overhead; 4. Recursive methods are prone to stack overflow, which is only suitable for academic learning; 5. Using Collections.reverse() is longer and has low performance; you should usually choose newStringBuilder(str).reverse().toString() because it is concise, fast and highly readable.

Aug 20, 2025 am 10:31 AM

java String reverse

How to extract a ZIP archive in Java?

Using ZipInputStream is a common method for decompressing ZIP files in Java. 1. First create the target directory; 2. Use ZipInputStream to read the ZIP file and process ZipEntry one by one; 3. Determine whether each entry is a directory. If so, create the corresponding folder. Otherwise, call extractFile to write the file content; 4. Use try-with-resources to ensure that the stream is closed correctly; 5. Pay attention to verifying the entry name to prevent path traversal attacks. This method is compatible and has fine control, and is suitable for most scenarios.

Aug 20, 2025 am 10:20 AM

Remove the first object instance of the specified class from Java ArrayList

This article describes how to remove the first object instance of the specified subclass T in Java's ArrayList. By using the instanceof keyword, the target object can be effectively identified and removed, avoiding inefficient ways to create new objects for comparison. At the same time, this article also discusses the possible problems that may exist when using the remove(Object o) method directly and provides a safer and more reliable solution.

Aug 20, 2025 am 10:06 AM

Mastering Java Streams API for Efficient Data Processing

The key to mastering JavaStreams API is to understand its core concepts and efficient usage methods: 1. Streams are not data structures, do not store elements, and can only be consumed once, and new streams need to be created for each processing; 2. Intermediate operations (such as filters, maps) are lazy, and terminal operations (such as collect, count) trigger actual calculations; 3. Priority is given to using primitive streams such as IntStream to avoid boxing overhead, and use parallelStream with caution, which is only enabled when large data volumes and CPU-intensive tasks; 4. Use Collectors to implement complex result processing such as grouping, partitioning, summary and string connection; 5. Flat-out nested structures using flatMap; 6. Encapsulation

Aug 20, 2025 am 09:58 AM

HC-05 Bluetooth and Android Multi-sensor Data Transmission and Analysis Practical Guide

This tutorial explains in detail how to use the HC-05 Bluetooth module to transmit data from multiple ultrasonic sensors to Android applications and realize independent display of data in different TextViews. The core strategies include the Arduino side using line breaks as packet separation, and the Android side ensuring the reception and parsing of complete messages through an efficient byte stream processing mechanism. The article will provide key code examples for Arduino and Android to guide readers to build a stable and reliable multi-channel sensor data communication system.

Aug 20, 2025 am 09:48 AM

How to convert a String to all lowercase in Java

To convert a string to lowercase, use the toLowerCase() method; 1. Directly call original.toLowerCase() to obtain a lowercase string; 2. To ensure cross-system consistency, locale should be specified, such as toLowerCase(Locale.ENGLISH); 3. When dealing with special languages (such as Turkish), you need to use the corresponding locale, such as toLowerCase(Locale.forLanguageTag("tr")); Since the string is immutable, the result must be assigned to a variable, and not specifying locale may cause unexpected behavior, so choose whether to specify lo according to your needs.

Aug 20, 2025 am 09:44 AM

Positioning runtime annotation processor: Tracking annotation processing logic using conditional breakpoints

This article aims to solve the challenge of the specific processing logic of running-time annotations (@Retention(RetentionPolicy.RUNTIME)) in large projects. When standard IDE tools cannot effectively reveal annotation processors, we will introduce an efficient debugging strategy. By setting breakpoints with specific conditions on the Java core API method Class.isAnnotationPresent(), developers can accurately track the code locations of reflective queries for specific annotations in third-party libraries or frameworks, thus revealing their underlying processing mechanism.

Aug 20, 2025 am 09:42 AM

Java vs Kotlin: Which JVM Language is Right for Your Next Project?

KotlinisthebetterchoiceformostnewJVM-basedprojects,especiallyAndroidapps,duetoitsconcisesyntax,built-innullsafety,coroutinesforasyncprogramming,andmodernlanguagefeaturesthatimprovedeveloperproductivityandcodemaintainability;1.Kotlinreducesboilerplate

Aug 20, 2025 am 09:37 AM

How to use Selenium WebDriver to close web ad pop-ups

This article aims to help developers solve the problem of closing ad pop-ups when using Selenium WebDriver to automate tests or web operations. We'll explore how to target and close ad popups located in iframes and how to switch back to the main document after the action is complete. Through this article, you will master effective ways to deal with such problems and ensure the stability and reliability of automated scripts.

Aug 20, 2025 am 09:36 AM

Solve Spring Boot Gradle project startup failure: Port 8080 has been occupied

This article aims to help developers resolve the error "Web server failed to start. Port 8080 was already in use." encountered when starting a Spring Boot Gradle project. By providing cross-platform (Windows, Unix/Linux/Mac) port occupancy detection methods and guidance on terminating the occupancy process, ensure that Spring Boot applications can be successfully up and running on the specified port.

Aug 20, 2025 am 09:15 AM

How to deal with mapping issues where Bean attributes are inconsistent with database column names in Spring JDBC

In Spring JDBC, when using BeanPropertyRowMapper for result set mapping, the default mapping mechanism may not work correctly if the property name of the Java Bean does not exactly match the column name of the database table, especially when there are non-standard naming conventions (such as prefixes). This article will explore the working principle and limitations of BeanPropertyRowMapper, and provide a robust solution: implement a custom RowMapper interface to accurately control the data mapping process, ensure that query results can be successfully mapped to POJO objects even if the column names vary greatly, and provide detailed code examples and usage guidance.

Aug 20, 2025 am 09:06 AM