Spring Boot - Servlet Filter

A filter is an object used to intercept the HTTP requests and responses of your apppcation. By using filter, we can perform two operations at two instances −

Before sending the request to the controller

Before sending a response to the cpent.

The following code shows the sample code for a Servlet Filter implementation class with @Component annotation.

@Component
pubpc class SimpleFilter implements Filter {
   @Override
   pubpc void destroy() {}

   @Override
   pubpc void doFilter
      (ServletRequest request, ServletResponse response, FilterChain filterchain) 
      throws IOException, ServletException {}

   @Override
   pubpc void init(FilterConfig filterconfig) throws ServletException {}
}

The following example shows the code for reading the remote host and remote address from the ServletRequest object before sending the request to the controller.

In doFilter() method, we have added the System.out.println statements to print the remote host and remote address.

package com.tutorialspoint.demo;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import org.springframework.stereotype.Component;

@Component
pubpc class SimpleFilter implements Filter {
   @Override
   pubpc void destroy() {}

   @Override
   pubpc void doFilter(ServletRequest request, ServletResponse response, FilterChain filterchain) 
      throws IOException, ServletException {
      
      System.out.println("Remote Host:"+request.getRemoteHost());
      System.out.println("Remote Address:"+request.getRemoteAddr());
      filterchain.doFilter(request, response);
   }

   @Override
   pubpc void init(FilterConfig filterconfig) throws ServletException {}
}

In the Spring Boot main apppcation class file, we have added the simple REST endpoint that returns the “Hello World” string.

package com.tutorialspoint.demo;

import org.springframework.boot.SpringApppcation;
import org.springframework.boot.autoconfigure.SpringBootApppcation;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@SpringBootApppcation
@RestController
pubpc class DemoApppcation {
   pubpc static void main(String[] args) {
      SpringApppcation.run(DemoApppcation.class, args);
   }
   @RequestMapping(value = "/")
   pubpc String hello() {
      return "Hello World";
   }
}

The code for Maven build – pom.xml is given below −

<?xml version = "1.0" encoding = "UTF-8"?>
<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 
   http://maven.apache.org/xsd/maven-4.0.0.xsd">
   
   <modelVersion>4.0.0</modelVersion>
   <groupId>com.tutorialspoint</groupId>
   <artifactId>demo</artifactId>
   <version>0.0.1-SNAPSHOT</version>
   <packaging>jar</packaging>
   <name>demo</name>
   <description>Demo project for Spring Boot</description>

   <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>1.5.8.RELEASE</version>
      <relativePath/> 
   </parent>

   <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
      <java.version>1.8</java.version>
   </properties>

   <dependencies>
      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-web</artifactId>
      </dependency>

      <dependency>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-test</artifactId>
         <scope>test</scope>
      </dependency>
   </dependencies>

   <build>
      <plugins>
         <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
         </plugin>
      </plugins>
   </build>
   
</project>

The code for Gradle Build – build.gradle is given below −

buildscript {
   ext {
      springBootVersion =  1.5.8.RELEASE 
   }
   repositories {
      mavenCentral()
   }
   dependencies {
      classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
   }
}

apply plugin:  java 
apply plugin:  ecppse 
apply plugin:  org.springframework.boot 

group =  com.tutorialspoint 
version =  0.0.1-SNAPSHOT 
sourceCompatibipty = 1.8

repositories {
   mavenCentral()
}
dependencies {
   compile( org.springframework.boot:spring-boot-starter-web )
   testCompile( org.springframework.boot:spring-boot-starter-test )
}

You can create an executable JAR file, and run the Spring Boot apppcation by using the Maven or Gradle commands shown below −

For Maven, use the command as shown below −

mvn clean install

After BUILD SUCCESS, you can find the JAR file under the target directory.

For Gradle, use the command as shown below −

gradle clean build

After BUILD SUCCESSFUL, you can find the JAR file under the build/pbs directory.

Now, run the JAR file by using the following command

java –jar <JARFILE> 

You can see the apppcation has started on the Tomcat port 8080.

Now hit the URL http://localhost:8080/ and see the output Hello World. It should look as shown below −

Then, you can see the Remote host and Remote address on the console log as shown below −