Physics Simulation       Lecture 12B Cloning File Read by Applet RandomIO,Append DecimalFormat DecimalFormat-IBM Precision Class-KI Format - Core Java Output to String Console Demo Exercises Lectures 1A: Introduction 1B: Java Intro 2A: BuildingBlocks 2B: Objects 3A: More Objects 3B: Exceptions        & Threads 4A: Waves 4B: Nuclear &        Particle 5A: AWT 5B: More AWT       & Graphics 6A:Detectors &       Simulation 6B: LHC/Atlas &      RandomSims     7A: Swing 7B: Java2D 8A: Java Apps 8B: Dialogs &     MoreClasses 9A: Java I/O 9B: Utilities,         Unicode 10A: More     Threading 10B: File     Handling 11A: Array,Print,     Images 11B: SimplePhysics     Simulation 12A: Tips &     Techniques 12B: More Tips &     Techniques 13A: Satellite     Simulations 13B: Intro to Java     Networking 14A: Java Servers 14B: HTTP Server 15A: ServerClient 15B: ServerClient    Expt.Simulation 16A: Course           Review 16B: ExerciseTest         Discussion     Contacts     Description     Exercises     Index     Outline     Q&A     Resources     StudentInfoForm     Student Pages     What's New

Home : Lectures : Lecture 12B : Reading a File from an Applet Reading a File from an Applet Often one of the first applets that new Java programmers want to write in their own work involves reading a file of some sort. This could be simple database info, e.g. a list or table of values and descriptions, in text format. We have learned to read image files and audio files from an applet but have not yet read a text file. This is fairly easy to do. However, keep in mind that the SecurityManager restricts access to only those files accessible from the location of the html and java files. Below we show the code to read a text file from an applet. Note that we use the URL class that is convenient for accessing web resources. This class provides various methods and fields, e.g. separate fields for the domain, path and file, that can be useful. In this case, it also provides a method to obtain file access through an InputStream. Then we can wrap this stream with an InputStreamReader to provide proper character handling. Finally, a BufferedReader is wrapped around the stream to provide buffering to smooth out the stream flow and also to get the readLine() method for grabbing a whole line at once and returning it in a string. ReadFile.java import java.applet.*; import java.awt.*; import java.io.*; import java.net.*; public class ReadFile extends Applet {   StringBuffer buf;   String FileToRead="message.txt";   TextArea ta; //--------------------------------------------------------   public void init() {     ta = new TextArea(40, 40);     ta.setEditable(false);     setLayout(new BorderLayout());     add(ta, "Center");     // Get setup parameters from applet html     String param = getParameter("FileToRead");     if ( param != null){       FileToRead = new String(param);     }     // Now read the file.     readFile();   } //--------------------------------------------------------   public void readFile(){     String line;     URL url=null;     try {      url = new URL (getCodeBase(), FileToRead );     }     catch (MalformedURLException  e ) {        System.out.println("Malformed URL ");        stop();     }       try {       InputStream in=url.openStream();       BufferedReader dis =           new BufferedReader(new InputStreamReader(in));       buf = new StringBuffer () ;       while ((line = dis.readLine()) != null){         buf.append(line + "\n");       }       in.close();     }     catch (IOException e ) {}     // Load the file into the TextArea.     ta.append(buf.toString ());   } }

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