File Handling in Java: Reading and Writing Data to the File

File handling is one of the key concepts in programming especially when dealing with data that is required to be stored, retrieved or processed outside the execution timeline of the application. In Java, the majority of the file handling is achieved by using input/output (I/O) streams and classes of the Java standard library. The functionality of file read and write operations is one of the basic features for any package that needs to save information in a file, regardless of whether a textual or binary form is implemented.

In this article, we shall delve into the basic principles of file management in Java using an example of reading from and writing to files. These types of operations are often required by the developers who want to build the applications which need to interact with external data. After reading this article, you should visibly be able to appreciate the scope of file handling in Java and how to conduct file input or output operations in your applications.

1. File Handling in Java: An Overview

It is to be noted that file handling in Java language falls into the scope of `java.io` package. This is because it has classes and methods for reading data from a file or writing data in a file. Generally interaction with files comprise of the following tasks:

1. Opening a file: We have to connect with the file before reading or writing any information.

2. Reading from a file: Program can get the content of the file for its further use.

3. Writing to a file: This can also be done by changing the required file by adding additions to its content

All of these activities are done through streams which is a feature in java to move data from one place to another. This includes transferring of files in java using its input and output.

2. Streams in Java

A stream is a concept that seems abstract but in reality it does represent the flow of data. Data transfer in files is done through streams where data in the form of bytes or characters can be read from or written to the files. In Java, there are two types of streams:


- Byte streams are ideal for reading image, audio or binary files or any other non text files. It works on the raw data files with byte streams.

- Character streams are the most convenient for reading and writing text files as they work on character data which is more suitable for text files.

Every stream class in Java has built in functions to read or write data, and if additional features, serializations or data buffering are needed the stream can be wrapped together with other stream classes.

3. Reading Files in Java

To extract data from a file it has to be accessed which involves opening the file and then reading it line by line. The most common technique is to use a stream that is most suitable for the file type and allows to view its content. Some common examples of the classes in Java which assist in reading files include but are not limited to `FileReader`, `BufferedReader`, and `FileInputStream`.

The `FileReader` class is a rather basic class used for reading files which are based on characters. It is suitable for text files, and it may benefit from being combined with a `BufferedReader` in order to speed up file operations, especially when reading large files. This technique is more efficient because, instead of reading character by character, the program reads blocks of data.

When reading from a file, it is important to be prepared for common errors, such as the case where the file does not exist or the file cannot be accessed. To catch and convey these types of errors, exceptions are utilized, and Java provides this feature.

Java has almost the same functionality since it provides a `BufferedReader` with its `readLine()` method so you can read files line by line. This method transfers line by line each string of the document which can then be worked with, as required, in a program. This method is effective and efficient while working with larger text files as it does not require the entire text to be read and stored in the memory all at once.

4. Writing Files in Java

The process is very similar when writing a file in Java, however, instead of fetching information from the given source, the application now inserts data into the source. This can be achieved with the use of classes like `FileWriter`, `BufferedWriter` and `FileOutputStream`.

The `FileWriter` class allows a user to apply a simple mechanism to write characters in the file. It can be applicable to write text files for example, and if it is used together with a `BufferedWriter` then text files become faster by buffering the records before they are written into the file. This makes the number of disk accesses fewer, which is critical especially when dealing with large volumes of data.

The purpose of the `BufferedWriter` in this case is performance since it is usually used together with `FileWriter` which has a buffered output stream thus data is written larger than one character at a time. The buffering provided by `BufferedWriter` is very helpful when writing a large amount of text data.

Where you wish to add data to a file that exists already, but do not want to overwrite it, you need to change the settings of the `FileWriter` constructor by adding a boolean parameter that sets it to append mode. This will guarantee that new data will be placed in the end of the file instead of overwriting it.

The other class that Java provides is the `PrintWriter` which is a relatively easier way of writing formatted data like numbers or strings to a file. This class contains a method such as `println()` which will write data onto the file with writing to the file and moving to the next line each time after the data is written onto the file.

5. Managing File Paths

File paths are used while working with files in Java. A path is considered a string of characters that show the position of the file in the system. One can be an absolute path while the other could be a relative path.

- Absolute path : As the name suggests, an absolute path is a partial path of the document starting from the root of the file system. For example, one can take "C:/Users/Username/Documents/file.txt" as an example of an absolute path.

- Relative path : Similarly a relative path identifies a file with respect to the present location of the working directory of the program. For example, if the program is running under a definite directory where the current file location is combined as data, one could use a relative path of data/file.txt.

Hence it is important to stress that you give the correct path to a file otherwise it would not be able to be located and extracted. Please note Java has an additional option of comprehending Paths which is encapsulated in the `java.nio.file` package. This will enable one to work with file locations with ease and regardless of the operating system.