FileReader

FileReader is a name used for two common programming interfaces that read file contents into a program: one in Java and one in the Web API available to JavaScript running in browsers. Both provide a way to obtain the textual or binary data stored in files, but they operate in different environments and have different usage patterns.

In Java, FileReader is a convenience class in the java.io package that reads character data from plain text files. It is a subclass of InputStreamReader and can be constructed with a file path or a File object, with an optional charset to specify the encoding. Because character encoding matters for correct interpretation of the file contents, FileReader is often wrapped in a BufferedReader to improve efficiency and to enable reading lines. When finished, the stream should be closed, typically using a try-with-resources statement to ensure proper resource management. While FileReader remains widely used for simple text input, newer code often prefers Files.newBufferedReader(Path, Charset) for more explicit control over encoding and resource handling.

In the browser, FileReader is a JavaScript API that reads File or Blob objects asynchronously. It offers methods such as readAsText, readAsArrayBuffer, and readAsDataURL, and communicates results through events like onload and onerror. Files or Blobs are usually obtained from an input element or a drag-and-drop operation. A notable point is that readAsBinaryString is deprecated, and for large files, developers may opt for streaming approaches or chunked reads to avoid blocking the main thread.

Overall, FileReader in both environments provides a straightforward means to access file data, with environment-specific considerations regarding encoding, performance, and error handling. See also the related input handling and stream-based APIs in the respective languages.