JAVA EE: How to filter components in auto scanning? | Spring Filter components in auto scanning

Friday, 31 August 2018

How to filter components in auto scanning? | Spring Filter components in auto scanning

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Overview: Filtering Components in Auto Scanning

In the Spring Framework, component scanning enables automatic detection and registration of beans marked with stereotypes such as @Component, @Repository, @Service, and @Controller. However, in larger enterprise applications, you often need fine-grained control over which classes get detected or excluded. Spring provides powerful filtering mechanisms using include-filter and exclude-filter options.

In this tutorial, you will learn how to customize component scanning by applying filters to include or exclude specific classes, annotations, or regex patterns in Spring.

Understanding Include and Exclude Filters

Spring's component scanning allows multiple filter types to customize bean registration:

Include Filters (include-filter): Extends component scanning to detect classes that may not even have standard stereotype annotations.
Exclude Filters (exclude-filter): Disallows specific classes or packages from being registered as beans, even if they have @Component annotations.
Filter Types Supported:
- annotation: Filter based on presence of a specific annotation.
- assignable: Filter based on whether a class extends or implements a class/interface.
- regex: Filter using regular expressions matching full class names.
- aspectj: Filter matching AspectJ type patterns.

How to Configure Filters

Specify the Base Package: Define the base package to be scanned inside <context:component-scan> or @ComponentScan.
Add Exclude or Include Filter: Define the filter criteria directly inside the scanning configuration:
<context:component-scan base-package="com.example"> <context:exclude-filter type="regex" expression=".*Test.*"/> </context:component-scan>
Bootstrap Application Context: When Spring starts up, it applies your custom filters, registering only the beans that pass your criteria.

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How to filter components in auto scanning? | Spring Filter components in auto scanning

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.2.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

    </dependencies>

</project>

EmployeeDAO.java

package com.ram.dao;

public class EmployeeDAO

{

    public void addEmployee()

    {

        System.out.println("inside EmployeeDAO addEmployee()");

    }

}

EmployeeService.java

package com.ram.service;

import org.springframework.beans.factory.annotation.Autowired;

import com.ram.dao.EmployeeDAO;

public class EmployeeService

{

    @Autowired

    EmployeeDAO employeeDAO;

    public void addEmployee()

    {

        System.out.println("inside EmployeeService addEmployee()");

        employeeDAO.addEmployee();

    }

    @Override

    public String toString()

    {

        return "EmployeeService [employeeDAO=" + employeeDAO + "]";

    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 

    xmlns:context="http://www.springframework.org/schema/context"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

    http://www.springframework.org/schema/beans/spring-beans-4.3.xsd

    http://www.springframework.org/schema/context

    http://www.springframework.org/schema/context/spring-context-4.3.xsd">

    <context:component-scan base-package="com.ram">

        <context:include-filter type="regex"

            expression="com.ram.dao.*DAO.*" />

        <context:include-filter type="regex"

            expression="com.ram.service.*Service.*" />

    </context:component-scan>

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.service.EmployeeService;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        System.out.println("---------------------------------------");

        EmployeeService employeeService = context.getBean("employeeService",

                EmployeeService.class);

        System.out.println(

                "Got employeeService object from the ApplicationContext(Spring Container)");

        System.out.println(employeeService);

        employeeService.addEmployee();

    }

}

Output

Aug 16, 2018 9:31:41 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Thu Aug 16 09:31:41 IST 2018]; root of context hierarchy

Aug 16, 2018 9:31:41 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

---------------------------------------

Got employeeService object from the ApplicationContext(Spring Container)

EmployeeService [employeeDAO=com.ram.dao.EmployeeDAO@782663d3]

inside EmployeeService addEmployee()

inside EmployeeDAO addEmployee()