Mocking is an essential part of unit testing, and the Mockito library makes it easy to write clean and intuitive unit tests for your Java code.
Get started with mocking and improve your application tests using our Mockito guide:
Handling concurrency in an application can be a tricky process with many potential pitfalls. A solid grasp of the fundamentals will go a long way to help minimize these issues.
Get started with understanding multi-threaded applications with our Java Concurrency guide:
Spring 5 added support for reactive programming with the Spring WebFlux module, which has been improved upon ever since. Get started with the Reactor project basics and reactive programming in Spring Boot:
Since its introduction in Java 8, the Stream API has become a staple of Java development. The basic operations like iterating, filtering, mapping sequences of elements are deceptively simple to use.
But these can also be overused and fall into some common pitfalls.
To get a better understanding on how Streams work and how to combine them with other language features, check out our guide to Java Streams:
Explore Spring Boot 3 and Spring 6 in-depth through building a full REST API with the framework:
Yes, Spring Security can be complex, from the more advanced functionality within the Core to the deep OAuth support in the framework.
I built the security material as two full courses - Core and OAuth, to get practical with these more complex scenarios. We explore when and how to use each feature and code through it on the backing project.
You can explore the course here:
Spring Data JPA is a great way to handle the complexity of JPA with the powerful simplicity of Spring Boot.
Get started with Spring Data JPA through the guided reference course:
Refactor Java code safely — and automatically — with OpenRewrite.
Refactoring big codebases by hand is slow, risky, and easy to put off. That’s where OpenRewrite comes in. The open-source framework for large-scale, automated code transformations helps teams modernize safely and consistently.
Each month, the creators and maintainers of OpenRewrite at Moderne run live, hands-on training sessions — one for newcomers and one for experienced users. You’ll see how recipes work, how to apply them across projects, and how to modernize code with confidence.
Join the next session, bring your questions, and learn how to automate the kind of work that usually eats your sprint time.
Distributed systems often come with complex challenges such as service-to-service communication, state management, asynchronous messaging, security, and more.
Dapr (Distributed Application Runtime) provides a set of APIs and building blocks to address these challenges, abstracting away infrastructure so we can focus on business logic.
In this tutorial, we'll focus on Dapr's pub/sub API for message brokering. Using its Spring Boot integration, we'll simplify the creation of a loosely coupled, portable, and easily testable pub/sub messaging system:
1. Introduction
In this tutorial, we’ll see how we use Java to delete the contents of a file without deleting the file itself. Since there are many simple ways to do it, let’s explore each one by one.
2. Using PrintWriter
Java’s PrintWriter class extends the Writer class. It prints the formatted representation of objects to the text-output stream.
We’ll perform a simple test. Let’s create a PrintWriter instance pointing to an existing file, deleting existing content of the file by just closing it, and then make sure the file length is empty:
new PrintWriter(FILE_PATH).close();
assertEquals(0, StreamUtils.getStringFromInputStream(new FileInputStream(FILE_PATH)).length());Also, note that if we don’t need the PrintWriter object for further processing, this is the best option. However, if we need the PrintWriter object for further file operations, we can do this differently:
PrintWriter writer = new PrintWriter(FILE_PATH);
writer.print("");
// other operations
writer.close();3. Using FileWriter
Java’s FileWriter is a standard Java IO API class that provides methods to write character-oriented data to a file.
Let’s now see how we can do the same operation using FileWriter:
new FileWriter(FILE_PATH, false).close();Similarly, if we need the FileWriter object for further processing, we can assign it to a variable and update with an empty string.
4. Using FileOutputStream
Java’s FileOutputStream is an output stream used for writing byte data to a file.
Now, let’s delete the content of the file using FileOutputStream:
new FileOutputStream(FILE_PATH).close();
5. Using Apache Commons IO FileUtils
Apache Commons IO is a library that contains utility classes to help out with common IO problems. We can delete the content of the file using one of its utility classes – FileUtils.
To see how this works, let’s add the Apache Commons IO dependency to our pom.xml:
<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.15.1</version>
</dependency>
After that, let’s take a quick example demonstrating deletion of file content:
FileUtils.write(new File(FILE_PATH), "", Charset.defaultCharset());6. Using Java NIO Files
We can also delete the file contents using java.nio.file.Files:
BufferedWriter writer = Files.newBufferedWriter(Paths.get(FILE_PATH));
writer.write("");
writer.flush();7. Using Java NIO FileChannel
Java NIO FileChannel is NIO’s implementation to connect a file. It also complements the standard Java IO package.
We can also delete the file contents using java.nio.channels.FileChannel:
FileChannel.open(Paths.get(FILE_PATH), StandardOpenOption.WRITE).truncate(0).close();8. Using Guava
Guava is an open source Java-based library that provides utility methods to do I/O operations. Let’s see how to use the Guava API for deleting the file contents.
First, we need to add the Guava dependency in our pom.xml:
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>31.0.1-jre</version>
</dependency>
After that, let’s see a quick example to delete file contents using Guava:
File file = new File(FILE_PATH);
byte[] empty = new byte[0];
com.google.common.io.Files.write(empty, file);9. Conclusion
To summarize, we’ve seen multiple ways to delete the content of a file without deleting the file itself.
