Java url download file

One channel will connect to the source and other to the target. Once the channels are set, we can transfer data between them. Next, is an example of using HttpClient to download a file and save it on the disk. First, we simply create an instance of HttpClient using its builder. Finally, we use the input stream from the HttpResponse and use File copy method to write it to a Path on disk.

This section explains how to asynchronously download a file from URL and save it to the disk. To do that, we can use sendAsync method of HttpClient, which will return a Future instance. When we execute an asynchronous method, the program execution will not wait for the method to finish. Instead it will progress further doing other stuff. We can check on the future instance to see if the execution is finished and the response is ready.

Next block of code demonstrates using HttpClient that downloads a file asynchronously and save onto the disk. As it is shown in the example, we are sending an async request, which returns a Future of InputStream.

Finally, we use Files copy method to write the file to disk. In this article, you will learn how to download a file using a URL in Java. Downloading a file through a Java code using a URL allows the Java application to download a file directly into a local system from a remote repository or any other local storage. This process reads a file from the URL and writes it to a local file. Java offers three different ways to download a file using a URL.

If we use Java without using any external library, it takes the file as input and reads those data byte by byte. The function uses two parameters, one URL link and the other file name. The stream of bytes will be read within this method using the while loop. The following catch block will handle any input-output exception and execute the printStackTrace. While using the Java IO library, the streams read the data byte by byte.

But in the Java NIO package, data are read as channels and buffers. Now, within the Main class, we have created the main. Inside the main and within the try block, we have created two String objects by the name fileLink and oppath where we have defined the URL link and the file location.

Then we have created an input stream for the file we want to download. The reason we use the BufferedInputStream class instead of the InputStream is its buffering ability that gives our code a performance boost. Before we dive deeper into the coding aspect let's take an overview of the classes and the individual functions we will be using in the process. The java. URL class in Java is a built-in library that offers multiple methods to access and manipulate data on the internet.

In this case, we will be using the openStream function of the URL class. The method signature for the openStream function is:. The openStream function works on an object of the URL class.

The URL class opens up a connection to the given URL and the openStream method returns an input stream which is used to read data from the connection. These classes are used for reading from a file and writing to it, respectively. The contents are read as bytes and copied to a file in the local directory using the FileOutputStream. To lower the number of lines of code we can use the Files class available from Java 7.

The Files class contains methods that read all the bytes at once and then copies it into another file. Here is how you can use it:. Java NIO is an alternative package to handle networking and input-output operations in Java.

The main advantage that the Java NIO package offers is that it's non-blocking, and has channeling and buffering capabilities. When we use the Java IO library we work with streams that read data byte by byte. However, the Java NIO package uses channels and buffers. The buffering and channeling capabilities allow the system to copy contents from a URL directly into the intended file without needing to save the bytes in application memory, which would be an intermediary step.

The ability to work with channels boosts performance. The downloaded contents will be transferred to a file on the local system via the corresponding file channel. After defining the file channel we will use the transferFrom method to copy the contents read from the readChannel object to the file destination using the writeChannel object. The transferFrom and transferTo methods are much more efficient than working with streams using a buffer.

The transfer methods enable us to directly copy the contents of the file system cache to the file on the system.