Example - Reading a URL
URLdemo, opens a connection to a web site specified by a URL (Uniform Resource Locator), for the purpose of reading text from a file at that site. It constructs an object of the Java API class,
java.net.URL, which enables convenient handling of URLs. Then, it calls a method on the URL object, to open a connection.
To read and display the lines of text at the site,
URLdemo uses classes from the Java I/O package
java.io. It creates an
InputStreamReader object, and then uses that object to construct a
BufferedReader object. Finally, it calls a method on the
BufferedReader object to read the specified number of lines from the site.
Description of URLdemo
The major tasks performed by
1. Construct a URL Object
The example first calls a constructor on
java.net.URL and assigns the resulting object to variable
URL constructor takes a single argument, the name of the URL to be accessed, as a string. The constructor checks whether the input URL has a valid form.
2. Open a Connection to the URL
The second statement of the example calls the method,
openStream, on the
url, to establish a connection with the web site named by the object. The method returns an
InputStream object to variable,
is, for reading bytes from the site.
3. Set Up a Buffered Stream Reader
The next two lines create a buffered stream reader for characters. The
java.io.InputStreamReader constructor is called with the input stream
is, to return to variable
isr an object that can read characters. Then, the
java.io.BufferedReader constructor is called with
isr, to return a
BufferedReader object to variable
br. A buffered reader provides for efficient reading of characters, arrays, and lines.
4. Read and Display Lines of Text
The final statements read the initial lines of HTML text from the site, displaying only the first 4 lines that contain meaningful text. Within the MATLAB
for statements, the
readLine reads each line of text (terminated by a
return and/or line feed character) from the site.
Running the Example
When you run this example, you see output similar to the following.
url = http://www.mathworks.com/support/tech-notes/1100/1109.shtml is = ice.net.CachedInputStream@7e700c isr = java.io.InputStreamReader@7e6696 br = java.io.BufferedReader@7e5d1b s = <p class="standard">This technical note provides an introduction to vectorization techniques. s = In order to understand some of the tricks available, an introduction to s = MATLAB indexing is provided. Then several vectorization techniques are s = discussed, in order of simplest to most complicated.
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