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Java Important.md

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Java helpful

How to use .md, click here.

1. Remember:

In maven project all the stuff in build path has to be under classpath.

2. Could not initialize class org.apache.maven.plugin.war.util.WebappStructureSerializer

Reason: It arises because, new eclipse need the "maven-war-plugin" to know which version it is and what class it want.

Solution: Add in pom.xml(full tag with data) org.apache.maven.plugins maven-war-plugin 3.3.1 ProjectName

3. The superclass "jakarta.servlet.http.HttpServlet" was not found on the Java Build Path

Reason: - It is not able to get the server to hold the jsp and servlets

Solution: Add dependency for the "jakarta.servlet.http.HttpServlet jakarta.servlet jakarta.servlet-api 6.0.0 provided 

<!-- lower then java 17  -->
<dependency>
	<groupId>javax.servlet</groupId>
	<artifactId>javax.servlet-api</artifactId>
	<version>4.0.1</version>
	<scope>provided</scope>
</dependency>
<dependency>
	<groupId>javax.servlet.jsp</groupId>
	<artifactId>javax.servlet.jsp-api</artifactId>
	<version>2.3.3</version>
	<scope>provided</scope>
</dependency>

4. JAR WAR

https://www.baeldung.com/java-jar-war-packaging

5. Versioning

<properties>
	<java.version>17</java.version>
	<maven.compiler.source>17</maven.compiler.source>
	<maven.compiler.target>17</maven.compiler.target>
</properties>

6. View page thymeLeaf

Install plugin from here first in Eclipse/STS
https://www.thymeleaf.org/eclipse-plugin-update-site/

7. Use Lombok

Install Lombok pc with: https://projectlombok.org/download Install plugin: https://projectlombok.org/p2

8. Note;

install software in eclipse to use lombok -> https://projectlombok.org/p2 thymeLeaf -> https://raw.githubusercontent.com/thymeleaf/thymeleaf-extras-eclipse-plugin/update-site/3.1.0/

9. Referenced file contains errors (http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd). For more information, right click on the message in the Problems View and select

Reason: No need to connect this line after hibernate version 5 Solution:

10. Keep the response structure:

{
	"code": 0,	// The cod must be custom to the project
	"msg": "Success",
	"data": {
		"key": value
	},
	"success": true
}

Topic 2

Similar search

commons text library in java for work to find similar string on base of score

Stream

  1. Find the distinct numbers:

     List<Integer> noOfTimes = arr.stream().filter(e -> Collections.frequency(arr, e) > 1).distinct().collect(Collectors.toList());

  2. Find the no of Times occurrence.

     Map<Object, Long> noOfTimes = arr.stream().collect(Collectors.groupingBy(p -> p, Collectors.counting()));

Folder File use

Folders

  1. META-INF: (manifest file) (to configure)

    The META-INF directory, if it exists, is used to store package and extension configuration data, including security, versioning, extension and services.

  2. WEB-INF: (Deployment Descriptor)

    The WEB-INF directory contains the deployment descriptors for the Web application ( web.xml and weblogic.xml ) and two subdirectories for storing compiled Java classes and library JAR files. These subdirectories are respectively named classes and lib.

Files

  1. web.xml

    web.xml file is the deployment descriptor of the web application and contains a mapping for servlets (prior to 3.0), welcome pages, security configurations, session timeout settings, etc.

Project now working

  1. Must check a). Project facelets (java version, Dynamic web module, Runtimes, and their versions) b). Added all the jars c). Deployment Assembly > Java Build Path Entries.

  2. Getting error of class Not found even after adding jar make sure you add the jar in "/ProjectNamE/src/main/webapp/WEB-INF/lib" and all is added in 'modulepath'

  3. Comparison between Modulepath and Classpath in Eclipse's Java Build Path settings:

Aspect Modulepath Classpath
Purpose Manages Java modules. Manages traditional Java projects.
Introduced In Java 9 and later. Pre-Java 9.
Use in Modular Projects Required for modular projects. Not applicable in modular projects.
Configuration in Eclipse Eclipse projects with module-info.java. Traditional Eclipse projects without module-info.java.
Contents Modules, module dependencies, and module-related settings. JAR files, directories, and other classpath entries.
Visibility Control Modules provide encapsulation, restricting access based on module declarations. No built-in visibility control; all classes are accessible.
Support for Java Modules Explicitly supports Java modules using module-info.java. Does not provide direct support for Java modules.
Use of Automatic Modules Automatic modules are supported (JARs without module-info.java). N/A. Automatic modules are not applicable.
Java Version Dependency Requires Java 9 and later. Compatible with earlier Java versions.
Project Structure Requires module-info.java file defining module structure. Typically does not include module-info.java.

Note: The usage of Modulepath and Classpath depends on the nature of your project. If you are working with modular projects introduced in Java 9 and later, you will use Modulepath. For traditional projects without modules, you will use Classpath. If you are working in a modular project, Eclipse will automatically configure the Java Build Path accordingly.