Java using resource files

Java IO — Reading a File from the resources

In this article, we are going to present several ways to read a file from the resources folder in Java. This article covers plain Java solutions and methods dedicated to Spring applications.

2. Read a file from resources using getResourceAsStream method

The most popular solution to read files from the resources folder is to use getResourceAsStream(. ) method available in the ClassLoader object.

Let’s demonstrate how this solution works using sample Java project with the following structure:

├── pom.xml └── src ├── main │ ├── java │ │ └── com │ │ └── frontbackend │ │ └── java │ │ └── io │ │ └── resources │ │ └── ReadResourcesUsingGetResourceAsStream.java │ └── resources │ └── example.txt └── test └── java 

Our example.txt file, placed in /src/main/resources folder, has the following content:

This is a sample file in resources folder 

Main Java class that reads example.txt file from the resources folder has the following structure:

package com.frontbackend.java.io.resources; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; public class ReadResourcesUsingGetResourceAsStream < public static void main(String[] args) throws IOException < ReadResourcesUsingGetResourceAsStream obj = new ReadResourcesUsingGetResourceAsStream(); StringBuilder out = new StringBuilder(); InputStream inputStream = obj.getClass() .getClassLoader() .getResourceAsStream("example.txt"); try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream))) < String line; while ((line = reader.readLine()) != null) < out.append(line); >> System.out.println(out.toString()); > > 

In this example we used getClassLoader().getResourceAsStream(. ) method available in Class object to load file from resources into byte-based stream.

To print InputStream we used one of the available methods to convert InputStream to String in Java

3. Reading a file from resources folder using getResource method

In the next approach, we used getResource(. ) method that returns the URL object for reading the resource, or null if the resource could not be found.

package com.frontbackend.java.io.resources; import java.io.File; import java.io.IOException; import java.net.URL; import java.nio.file.Files; public class ReadResourcesUsingGetResource < public static void main(String[] args) throws IOException < ReadResourcesUsingGetResource obj = new ReadResourcesUsingGetResource(); URL url = obj.getClass() .getClassLoader() .getResource("example.txt"); File file = new File(url.getFile()); String content = new String(Files.readAllBytes(file.toPath())); System.out.println(content); >> 

In this example we make a use of getClassLoader().getResource(. ) method to get URL of our example.txt file locate in resources folder. Then we used getFile(. ) method to convert URL into File object.

You have many options to read a file in Java. In this example we used Files.readAllBytes(. ) method that simply convert InputStream to String in a one line.

4. Read a file from resources in the Spring project using ResourceUtils

ResourceUtils class comes with utility methods for resolving resource locations to files. We can use it to get a file from the resources folder in Spring applications.

In this example we will use Spring project with the following structure:

├── pom.xml └── src ├── main │ ├── java │ │ └── com │ │ └── frontbackend │ │ └── springboot │ │ └── Application.java │ └── resources │ └── example.txt 

Spring boot main class contains a simple REST controller that will return the content of example.txt file from available in the resources folder:

package com.frontbackend.springboot; import java.io.File; import java.io.IOException; import java.nio.file.Files; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.util.ResourceUtils; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; @SpringBootApplication @RestController public class Application < @GetMapping("/") public String getResourceFile() throws IOException < File file = ResourceUtils.getFile("classpath:example.txt"); return new String(Files.readAllBytes(file.toPath())); >public static void main(String[] args) < SpringApplication.run(Application.class, args); >> 

The application runs on default port 8080. When you enter http://location:8080 address in your browser you will see the content of the example.txt file.

5. Conclusion

In this tutorial, we presented several ways to get a file from the resources folder in Java. In Spring applications we have dedicated utility class that will do all the job for us. In plain Java we need to use getResourceAsStream(. ) or getResource(. ) method. In many situations, we want to read the file and process it so the natural way is to use the getResourceAsStream(. ) approach that returns byte-based stream we can process right away.

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How to Access Resource Files in Java: A Comprehensive Guide

Learn different methods for accessing resource files in Java, including com.google.common.io.Resources.getResource and getClass().getResourceAsStream. Get best practices for accessing resource files and avoid File API. Find out how to access resources from a Java library packed into its own .jar file.

• Use com.google.common.io.Resources.getResource to read the url of a file
• Do not use File API to get resource files
• How to create a Resource folder in Java with IntelliJ and
• Use getClass().getResourceAsStream(«/package/folder/foo.properties») to load a file from resources directory in Java
• Use getResourceAsStream() method to load resources from a .jar file
• Java programs can use two mechanisms to access resources: Applet.getCodeBase() and extending the base URL
• The resources folder belongs to the Maven project structure for configuration and data files
• Use Class.getResourceAsStream() to retrieve an InputStream to a file
• Use Statistika.class.getClassLoader().getResource(filename) to get a file from a resource folder
• Other helpful code examples on accessing resource files in Java
• Conclusion
• How to read resource file from jar in Java?
• How to access files in src main resources in Java?
• How do I get resources in Java?
• How to read file from test resources folder in Java?

Resource files are essential in Java programming for accessing configuration and data files. These files often contain valuable information such as database credentials, application properties, configuration values, and other data essential to the application’s operation. As such, it is imperative to know how to access these files in Java. In this blog post, we will provide a guide on how to access resource files in Java, including how to access resources from a Java library packed into its own .jar file.

Use com.google.common.io.Resources.getResource to read the url of a file

The com.google.common.io.Resources.getResource method allows Java developers to read the URL of a file as a resource. This method is simple and straightforward to use, making it a popular choice amongst Java developers. The method’s signature is as follows:

public static URL getResource(String resourceName) 

The method takes a single argument, which is the name of the resource file. The method returns a URL object that represents the URL of the file. The following code example demonstrates how to use the com.google.common.io.Resources.getResource method:

URL resource = Resources.getResource("myresource.txt"); 

Do not use File API to get resource files

It is essential to note that the File API should not be used to access resource files. This is because resource files are often packaged inside the JAR file and are not accessible as a regular file in the file system. Attempting to access resource files using the File API will result in a FileNotFoundException being thrown. Instead, Java developers should use the methods that are specifically designed to access resource files.

How to create a Resource folder in Java with IntelliJ and

I will be showcasing how to create a resource folder in Intellij, and I will create a method that Duration: 5:02

Use getClass().getResourceAsStream(«/package/folder/foo.properties») to load a file from resources directory in Java

The getClass().getResourceAsStream method is another popular way of accessing resource files in Java. This method allows Java developers to load a resource file as an InputStream. The method’s signature is as follows:

public InputStream getResourceAsStream(String name) 

The method takes a single argument, which is the name of the resource file. The following code example demonstrates how to use the getClass().getResourceAsStream method to load a file from the resources directory in Java:

InputStream input = getClass().getResourceAsStream("/myresource.txt"); 

Use getResourceAsStream() method to load resources from a .jar file

Java developers can also use the getResourceAsStream method to access resource files that are packaged inside a .jar file. The method’s signature is as follows:

public InputStream getResourceAsStream(String name) 

The method takes a single argument, which is the name of the resource file. The following code example demonstrates how to use the getResourceAsStream method to load resources from a .jar file:

InputStream input = getClass().getResourceAsStream("/myresource.txt"); 

Java programs can use two mechanisms to access resources: Applet.getCodeBase() and extending the base URL

Java developers can use two mechanisms to access resources in their programs: Applet.getCodeBase() and extending the base URL. The Applet.getCodeBase() method returns the base URL for the codebase, while extending the base URL allows Java developers to access resource files that are outside the codebase. The following code example demonstrates how to use these mechanisms to access resource files in Java:

URL url = new URL(getCodeBase(), "myresource.txt"); URL url = new URL(new URL("http://example.com"), "myresource.txt"); 

The resources folder belongs to the Maven project structure for configuration and data files

In Maven projects, the resources folder is used to store configuration and data files. The resources folder is located in the src/main directory and is automatically included in the build. The following code example demonstrates how to access resources from the resources folder in a Maven project:

InputStream input = getClass().getResourceAsStream("/myresource.txt"); 

Use Class.getResourceAsStream() to retrieve an InputStream to a file

The Class.getResourceAsStream method is another way of accessing resource files in Java. This method allows Java developers to retrieve an InputStream to a file. The method’s signature is as follows:

public InputStream getResourceAsStream(String name) 

The method takes a single argument, which is the name of the resource file. The following code example demonstrates how to use the Class.getResourceAsStream method to retrieve an InputStream to a file:

InputStream input = getClass().getResourceAsStream("/myresource.txt"); 

Use Statistika.class.getClassLoader().getResource(filename) to get a file from a resource folder

Java developers can also use the Statistika.class.getClassLoader().getResource(filename) method to get a file from a resource folder. The following code example demonstrates how to use this method to get a file from a resource folder:

InputStream input = Statistika.class.getClassLoader().getResourceAsStream("myresource.txt"); 

Other helpful code examples on accessing resource files in Java

In java, java resource file code example

File file = new File( getClass().getClassLoader().getResource("database.properties").getFile() );

In java, java resource file code example

InputStream inputStream = getClass() .getClassLoader().getResourceAsStream("database.properties");

In java, java resource file code example

 ClassLoader classloader = Thread.currentThread().getContextClassLoader(); InputStream is = classloader.getResourceAsStream("test.csv");

Conclusion

Accessing resource files in Java is essential for accessing configuration and data files. Different methods for accessing resource files include com.google.common.io.Resources.getResource, getClass().getResourceAsStream, and getResourceAsStream. Best practices for accessing resource files include proper naming conventions and avoiding the File API. Java programming offers platform independence, security , and scalability, but also has limitations such as slow performance and the need for frequent updates. cheatsheets for java programming can be found online for quick reference, and common issues with accessing resource files include incorrect file paths and naming conventions.

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