With this example we are going to demonstrate how to use the Non-blocking I/O API, or NIO.2 API (NIO API) for short, to read the contents of a file. The examples in this article are compiled and run in a Mac OS unix environment.
Please note that Java SE 8 is required to run the code in this article.
1. Introduction to the NIO API
The NIO.2 API was introduced in Java 7 as a replacement for the java.io.File class. It provides a flexible, and intuitive API for use with files.
2. Creating a NIO Path
In order to read a file from the file system we must first create a Path to the file. A Path object is a hierarchical representation of the path on a system to the file or directory. The java.nio.file.Path interface is the primary entry point for working with the NIO 2 API.
The easiest way to create a Path Object is to use the java.nio.files.Paths factory class. The class has a static get() method which can be used to obtain a reference to a file or directory. The method accepts either a string, or a sequence of strings(which it will join to form a path) as parameters. A java.nio.file.Path , like a File, may refer to either an absolute or relative path within the file system. This is displayed in the following examples:
Path p1 = Paths.get("cats/fluffy.jpg");
Path p2 = Paths.get("/home/project");
Path p3 = Paths.get("/animals", "dogs", "labradors");
In the above:
- p1 creates a relative reference to a file in the current working directory.
- p2 creates a reference to an absolute directory in a Unix based system.
- p3 creates a reference to the absolute directory /animals/dogs/labradors
3. Reading files with the NIO API
Once we have a Path Object we are able to execute most of the operations that were previously possible with java.io.File.
3.1 Using NIO API with newBufferedReader()
The NIO.2 API has methods for reading files using java.io streams. The Files.newBufferedReader(Path,Charset) reads the file found at the Path location, using the specified Charset for character encoding. Here’s an example:
Path path = Paths.get("src/main/resources/shakespeare.txt");
try(BufferedReader reader = Files.newBufferedReader(path, Charset.forName("UTF-8"))){
String currentLine = null;
while((currentLine = reader.readLine()) != null){//while there is content on the current line
System.out.println(currentLine); // print the current line
}
}catch(IOException ex){
ex.printStackTrace(); //handle an exception here
}
3.2 Using NIO API with readAllLines()
Another option is to use the Files.readAll() method, which will read the contents of a file and return them as an ordered list of strings. Here’s an example of this method:
Path path = Paths.get("src/main/resources/shakespeare.txt");
try{
List contents = Files.readAllLines(path);
//Read from the stream
for(String content:contents){//for each line of content in contents
System.out.println(content);// print the line
}
}catch(IOException ex){
ex.printStackTrace();//handle exception here
}
NOTE: The readAllLines() method first commits the contents of the file to memory, as a result you may encounter an Download NOW!
