Standard File Writing

• 1). The FileOutputStream class in the java.io package is the standard way to write data out to a file in the operating system. The constructor FileOutputStream(String name) will create a new FileOutputStream pointing to the filename specified by the string.
  
  Example:
  
  FileOutputStream fos = new FileOutputStream("/var/log/mylog.txt");
  
  
• 2). The standard PrintWriter class in the java.io package provides the easiest-to-use method of writing lines of data to an OutputStream. The constructor PrintWriter(OutputStream out) will create a new PrintWriter using the provided OutputStream. Combine this with the FileOutputStream as in the following example:
  
  FileOutputStream fos = new FileOutputStream("/var/log/mylog.txt");
  PrintWriter pw = new PrintWriter(fos);
  
  
• 3). To write a line data to the output stream, use the PrintWriter's method println(String x). This will write a line terminated string of data to the OutputStream.
  
  Example:
  
  FileOutputStream fos = new FileOutputStream("/var/log/mylog.txt");
  PrintWriter pw = new PrintWriter(fos);
  pw.println("This is a line of data");
  
  
• 4). When finished writing to the file, be sure to close both the PrintWriter and the FileOutputStream objects so that they release the resources associated with writing to the file.
  
  Example:
  
  FileOutputStream fos = new FileOutputStream("/var/log/mylog.txt");
  PrintWriter pw = new PrintWriter(fos);
  pw.println("This is a line of data");
  pw.close();
  fos.close();
  
  

JSP-Specific Techniques

• 1). To get a path that is relative to the current web application in your JSP container, use the ServletContext.getRealPath(String path) method.
  
  Example:
  
  String real_filename = context.getRealPath("/mylog.txt");
  
  
• 2). To embed the logic to write to a file into a JSP page, wrap the Java code in <% and %> and include the page directive to import the java.io.* classes.
  
  Example:
  
  <%@ page import="java.io.*" %>
  <%
  try {
  String real_filename = context.getRealPath("/mylog.txt");
  FileOutputStream fos = new FileOutputStream(real_filename);
  PrintWriter pw = new PrintWriter(fos);
  pw.println("This is a line of data");
  pw.close();
  fos.close();
  }
  catch (Exception e) {
  // Handle exceptions
  }
  %>
  
  Note the try...catch block that catches exceptions from the I/O operations. This is required because the FileOutputStream and PrintWriter classes' methods may throw an exception.
  
  
• 3). To write a parameter passed to the JSP page with the request.getParameter(String name) method into the text file, use the following example:
  
  <%@ page import="java.io.*" %>
  <%
  try {
  String real_filename = context.getRealPath("/mylog.txt");
  FileOutputStream fos = new FileOutputStream(real_filename);
  PrintWriter pw = new PrintWriter(fos);
  pw.println("This is a line of data");
  pw.println(request.getParameter("test"));
  pw.close();
  fos.close();
  }
  catch (Exception e) {
  // Handle exceptions
  }
  %>