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Java tutorial

Detailed analysis of log4j configuration file

1. Advantages of Log4j Log4j is an open source project of Apache. By using Log4j, we can control the delivery location of log information; we can also control the output format of each log; by defining the level of each log information, we can be more Car

2024-11-20
How to use NetworkInterface to obtain the server MAC address

Many times, we need to obtain server hardware information (such as MAC address). There are several commonly used methods: using a command line program to obtain hard disk information, then obtaining the output stream through Runtime.getRuntime().exec, and

2024-11-20
A brief analysis of the problem that Java Mail cannot parse the recipient list with semicolon

Today, a colleague encountered a problem. When using JAVA MAIL to receive emails, if the recipient is a list and the recipient list is separated by semicolons, an exception will occur in JAVA MAIL and cannot be parsed normally. I took a moment to take a l

2024-11-20
Quickly solve the bug that the commons-fileupload component cannot handle custom head information

Jakarta commons fileupload component can handle HTTP requests and responses. It is often used to handle file uploads. However, it was recently discovered that when we customize file uploads, assemble mime information ourselves, and add custom head nodes w

2024-11-20
How to simulate SSH operations using Ganymed SSH-2

Official address: http://www.cleondris.ch/en/opensource-ssh2.php Introduction: Ganymed SSH-2 for Java is a library which implements the SSH-2 pro

2024-11-20
Solution to the problem 501 Command "HELO" requires an argument

Scenario description: When saving the mailbox configuration, it automatically detects whether the mailbox configuration parameters are correct. It is found that when detecting SMTP, the system reports the following exception: Copy the code. The code is as

2024-11-20
Detailed explanation of the initialization sequence of elements in java classes

Copy the code. The code is as follows: public class Test4 {@Testpublic void test(){child child = new child();}}class parent{public static String paren

2024-11-20
Share what you should pay attention to when using Preferences to read and write the registry in JAVA

There is only one thing to pay attention to, that is, the key name or item name should not contain capital letters, otherwise the data cannot be read. The code is like this: Copy the code The code is as follows: Preferences preferences = Preferences.syste

2024-11-20
Reasons and solutions for why sudo command cannot be used when starting Java under Linux system

Operating system: centos 5.2 Scenario description: We have a WEB project. The customer requires that it be run as a normal user (such as chb). Then there is a button on the page. After clicking, you can shut down the computer. Implementation method: 1. JA

2024-11-20
In-depth analysis of java string class methods

Copy the code as follows: import java.nio.charset.Charset;import java.nio.charset.UnsupportedCharsetException;import java.util.Locale;imp

2024-11-20
In-depth analysis of locale in java

In projects, we often need to parse strings into Locales, but there is no easy-to-use class. Java itself provides 3 constructors, but in actual use, you need to parse them yourself, which is relatively cumbersome. Locale(langugae)locale(language,country)

2024-11-20
Velocity basic syntax introduction

1. Basic syntax 1. "#" is used to identify Velocity script statements, including #set, #if, #else, #end, #foreach, #end, #iinclude, #parse, #macro, etc.; such as: #if ($info.imgs)

2024-11-20
Comprehensive analysis of hashtable in java

Hashtables provide a useful way to optimize application performance. Hashtables are not a new concept in the computer field. They were designed to speed up computer processing, which is very slow by today's standards, while they allow you to query man

2024-11-20
Java custom error class sample code

In the program, an exception needs to be thrown, and then the error message is output in the user interface. One situation is to catch exceptions one by one when the last UI is displayed in the program, and then display the corresponding ErrorMessage. Som

2024-11-20
A brief analysis of the difference between ArrayList and Vector and the difference between HashMap and Hashtable in java

ArrayList and Vector mainly come from two aspects. 1. Synchronicity: Vector is thread-safe, which means it is synchronous, while ArrayList is thread-safe and not synchronous. 2. Data growth: when growth is needed ,Vector grows by one level by default, but

2024-11-20

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