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Spring Resource tutorial

Spring Resource tutorial shows how to use Resource to work with various resources in a Spring application.

Spring is a popular Java application framework for creating enterprise applications.

Spring Resource

Resource abstracts from the actual type of an underlying resource, such as a file or class path resource. It can be used to identify local or remote resources.

Spring ApplicationContext contains the getResource() method, which returns a resource handle for the specified resource type. It can be a classpath, file, or URL resource.

Spring Resource example

The application uses Spring's Resource to read a local file and a remote web page.

pom.xml
src
├───main
│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           └───service
│   │                   MyService.java
│   └───resources
│           logback.xml
│           words.txt
└───test
    └───java

This is the project structure.

pom.xml
<?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.zetcode</groupId>
    <artifactId>resourceex</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
        <spring-version>5.1.3.RELEASE</spring-version>

    </properties>

    <dependencies>

        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring-version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring-version}</version>
        </dependency> 
        
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.6.0</version>
                <configuration>
                    <mainClass>com.zetcode.Application</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

In the pom.xml file, we have basic Spring dependencies spring-core, spring-context, and logging logback-classic dependency.

The exec-maven-plugin is used for executing Spring application from the Maven on the command line.

resources/logback.xml
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <logger name="org.springframework" level="ERROR"/>
    <logger name="com.zetcode" level="INFO"/>

    <appender name="consoleAppender" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <Pattern>%d{HH:mm:ss.SSS} %blue(%-5level) %magenta(%logger{36}) - %msg %n
            </Pattern>
        </encoder>
    </appender>

    <root>
        <level value="INFO" />
        <appender-ref ref="consoleAppender" />
    </root>
</configuration>

The logback.xml is a configuration file for the Logback logging library.

resources/words.txt
clean
sky
forest
blue
crystal
cloud
river

The words.txt file contains a couple of words.

com/zetcode/MyService.java
package com.zetcode.service;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.stereotype.Service;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

@Service
public class MyService {

    private static final Logger logger = LoggerFactory.getLogger(MyService.class);

    @Autowired
    private ApplicationContext ctx;

    public void readWebPage() {

        var res = ctx.getResource("http://webcode.me");

        try (var is = new InputStreamReader(res.getInputStream());
                var bis = new BufferedReader(is)) {

            bis.lines().forEach(System.out::println);

        } catch (IOException ex) {
            logger.warn("{}", ex);
        }
    }

    public void readFile() {

        // var res = ctx.getResource("file:C:/Users/Jano/Documents/words.txt");
        var res = ctx.getResource("classpath:words.txt");

        try (var is = new InputStreamReader(res.getInputStream());
                var bis = new BufferedReader(is)) {

            bis.lines().forEach(System.out::println);

        } catch (IOException ex) {
            logger.warn("{}", ex);
        }
    }
}

The MyService has two methods that read a web page and a local text file.

@Autowired
private ApplicationContext ctx;

We inject the ApplicationContext. We use its getResource() method to get resource handlers.

var res = ctx.getResource("http://webcode.me");

We get a Resource from a web page.

// var res = ctx.getResource("file:C:/Users/Jano/Documents/words.txt");
var res = ctx.getResource("classpath:words.txt");

We can get a Resource from an absoute file path or a classpath.

com/zetcode/Application.java
package com.zetcode;

import com.zetcode.service.MyService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;

@ComponentScan(basePackages = "com.zetcode")
public class Application {

    private static final Logger logger = LoggerFactory.getLogger(Application.class);

    @Autowired
    private MyService myService;

    public static void main(String[] args) {

        var ctx = new AnnotationConfigApplicationContext(Application.class);
        var app = ctx.getBean(Application.class);

        app.run();
        ctx.close();
    }

    public void run() {

        myService.readWebPage();
        myService.readFile();
    }
}

This is the main application class.

@Autowired
private MyService myService;

A service bean is injected into the class with @Autowired.

myService.readWebPage();
myService.readFile();

We call the myService methods.

In this tutorial, we have shown how to use Resource to read a local text file and a web page.

You might also be interested in these related tutorials: Spring @Qualifier annotation tutorial, Spring Singleton scope bean, Spring c-namespace tutorial, Spring BeanDefinitionBuilder tutorial, Spring bean reference tutorial, and Java tutorial.