Class Cache

java.lang.Object

Cache

public class Cache
extends java.lang.Object

Cache represents a web page cache. A Cache object responds to requests for a web page (given the URL). See requestPage() for details. The cache maintains a count of the number of URL requests received. The cache maintains a count of the total number of pages fetched from the Internet.

Version:

2012.11.8

Author:

John Dalbey

Field Summary

Fields

Modifier and Type	Field and Description
static int	kDefaultCapacity Default cache capacity

Constructor Summary

Constructors

Constructor and Description
Cache() Construct a Cache with the default capacity.
Cache(int capacity) Construct a Cache with the specified capacity.

Method Summary

Methods

Modifier and Type	Method and Description
java.util.ArrayList<WebPage>	getPageList() Return an ordered list of all WebPages in the cache (using the default ordering).
int	getRequestCount() Return the number of URL requests received.
int	getUrlFetchCount() Return the total number of pages fetched from the Internet.
void	processUrls(java.io.Reader instream) Call requestPage() for every url in the input stream available at the provided Reader.
java.lang.String	requestPage(java.lang.String url) Respond to a request for a web page (given the URL).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

kDefaultCapacity

public static final int kDefaultCapacity

Default cache capacity

See Also:

Constant Field Values

Constructor Detail

Cache

public Cache()

Construct a Cache with the default capacity.

Cache

public Cache(int capacity)

Construct a Cache with the specified capacity.

Parameters:

capacity - the max number of entries in the cache

Precondition:

capacity > 0

Method Detail

processUrls

public void processUrls(java.io.Reader instream)

Call requestPage() for every url in the input stream available at the provided Reader. Each url is on a separate line and may include leading or trailing blanks. Ignore the value returned by requestPage().

Parameters:

instream - a Reader for the stream of url requests,

Postcondition:

the urls have been counted, the number of page fetches from web have been counted.

requestPage

public java.lang.String requestPage(java.lang.String url)

Respond to a request for a web page (given the URL). If the specified URL is not in the cache, the page is fetched and the content saved in the cache, along with a counter (initially, 1). On subsequent requests for the same URL, the cached page will be returned without needing to retrieve the page from the URL (and its counter incremented). The cache has a finite size, and when the cache fills up any subsequent requests cause the lowest frequency cached item to be removed, and the new request added. (If multiple entries have the same low frequency, an arbitrary one will be removed.)

Parameters:

url - the URL of the page to be returned

Returns:

String contents of the page at the given URL, or an empty string if the URL is malformed.

See Also:

MalformedURLException

Postcondition:

If the URL is well-formed, requestCount for this cache has been incremented.

getPageList

public java.util.ArrayList<WebPage> getPageList()

Return an ordered list of all WebPages in the cache (using the default ordering).

Returns:

ArrayList of ordered WebPages.

getRequestCount

public int getRequestCount()

Return the number of URL requests received.

Returns:

int number of URL requests received.

getUrlFetchCount

public int getUrlFetchCount()

Return the total number of pages fetched from the Internet.

Returns:

int total number of pages fetched from the Internet.