DZone Snippets: java code

avoid web caching

remvee (Remco van 't Veer) — Mon, 25 Sep 2006 00:28:46 GMT



// Set to expire far in the past.

response.setHeader("Expires", "Sat, 6 May 1995 12:00:00 GMT");

// Set standard HTTP/1.1 no-cache headers.

response.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");

// Set IE extended HTTP/1.1 no-cache headers (use addHeader).

response.addHeader("Cache-Control", "post-check=0, pre-check=0");

// Set standard HTTP/1.0 no-cache header.

response.setHeader("Pragma", "no-cache");

time based cache

remvee (Remco van 't Veer) — Thu, 03 Aug 2006 18:27:52 GMT

A simple time based cache build around a map store.



import java.util.Map;

import java.util.WeakHashMap;



/**

 * Simple time-based cache.

 */

public class SimpleCache {

	private long maxAge;

	private Map store;



	/**

	 * Instanciate a cache with max age of 1 hour and a WeakHashMap as store.

	 * @see java.util.WeakHashMap

	 */

	public SimpleCache() {

		this.maxAge = 1000 * 60 * 60;

		this.store = new WeakHashMap();

	}

	

	/**

	 * @param maxAge maximum age of an entry in milliseconds

	 * @param store map to hold entries

	 */

	public SimpleCache(long maxAge, Map store) {

		this.maxAge = maxAge;

		this.store = store;

	}

	

	/**

	 * Cache an object.

	 * @param key unique identifier to retrieve object

	 * @param value object to cache

	 */

	public void put(Object key, Object value) {

		store.put(key, new Item(value));

	}

	

	/**

	 * Fetch an object.

	 * @param key unique identifier to retrieve object

	 * @return an object or null in case it isn't stored or it expired

	 */

	public Object get(Object key) {

		Item item = getItem(key);

		return item == null ? null : item.payload;

	}

	

	/**

	 * Fetch an object or store and return output of callback.

	 * @param key unique identifier to retrieve object

	 * @param block code executed when object not in cache

	 * @return an object

	 */

	public synchronized Object get(Object key, Callback block) {

		Item item = getItem(key);

		if (item == null) {

			Object value = block.execute();

			item = new Item(value);

			store.put(key, item);

		}

		return item.payload;

	}

	

	/**

	 * Remove an object from cache.

	 * @param key unique identifier to retrieve object

	 */

	public void remove(Object key) {

		store.remove(key);

	}

	

	/**

	 * Get an item, if it expired remove it from cache and return null.

	 * @param key unique identifier to retrieve object

	 * @return an item or null

	 */

	private Item getItem(Object key) {

		Item item = (Item) store.get(key);

		if (item == null) {

			return null;

		}

		if (System.currentTimeMillis() - item.birth > maxAge) {

			store.remove(key);

			return null;

		}

		return item;		

	}



	/**

	 * Value container.

	 */

	private static class Item {

		long birth;

		Object payload;

		Item(Object payload) {

			this.birth = System.currentTimeMillis();

			this.payload = payload;

		}

	}

	

	/**

	 * A visitor interface.

	 */

	public static interface Callback {

		Object execute();

	}

}

And a couple of junit tests:



import java.util.HashMap;



import junit.framework.TestCase;



public class SimpleCacheTest extends TestCase {

	public void testPutGet () {

		SimpleCache c = new SimpleCache(Long.MAX_VALUE, new HashMap());

		c.put("key1", "value1");

		assertEquals("value1", c.get("key1"));

		c.put("key1", "value1.0");

		assertEquals("value1.0", c.get("key1"));

		c.put("key2", "value2");

		assertEquals("value2", c.get("key2"));

		assertEquals("value1.0", c.get("key1"));

	}

	

	public void testMaxAge () throws InterruptedException {

		SimpleCache c = new SimpleCache(1000, new HashMap());

		c.put("key1", "value1");

		assertEquals("value1", c.get("key1"));

		Thread.sleep(1500);

		assertNull(c.get("key1"));

		

		c.put("key2", "value2");

		Thread.sleep(750);

		c.put("key3", "value3");

		Thread.sleep(750);

		assertNull(c.get("key2"));

		assertNotNull(c.get("key3"));

		Thread.sleep(750);

		assertNull(c.get("key3"));

	}

	

	public void testRemove () {

		SimpleCache c = new SimpleCache(Long.MAX_VALUE, new HashMap());

		c.remove("key");

		assertNull(c.get("key"));

		c.put("key", "value");

		assertNotNull(c.get("key"));

		c.remove("key");

		assertNull(c.get("key"));

	}

	

	public void testCallBack () {

		SimpleCache c = new SimpleCache(Long.MAX_VALUE, new HashMap());

		assertEquals("value1", c.get("key1", new SimpleCache.Callback() {

			public Object execute() {

				return "value1";

			}

		}));

		assertEquals("value1", c.get("key1"));

		

		// again with a new callback (value)

		c.get("key1", new SimpleCache.Callback() {

			public Object execute() {

				return "value2";

			}

		});

		assertEquals("value1", c.get("key1"));

	}

}

Slurp InputStream to String

remvee (Remco van 't Veer) — Fri, 05 Aug 2005 17:52:14 GMT



public static String slurp (InputStream in) throws IOException {

    StringBuffer out = new StringBuffer();

    byte[] b = new byte[4096];

    for (int n; (n = in.read(b)) != -1;) {

        out.append(new String(b, 0, n));

    }

    return out.toString();

}

find files in zip, jar, war, ear and nested archives

remvee (Remco van 't Veer) — Tue, 31 May 2005 22:47:40 GMT

The following java class takes two arguments; a directory name and a regular expression. The directory is searched for files matching the regexp. Zip files (and zip-alikes) are also searched including nested zips.



import java.io.*;

import java.util.*;

import java.util.zip.*;



public class Finder {

	public static void main(String[] args) throws Exception {

		String path = args[0];

		final String expr = args[1];



		List l = new ArrayList();

		findFile(new File(path), new P() {

			public boolean accept(String t) {

				return t.matches(expr) || isZip(t);

			}

		}, l);



		List r = new ArrayList();

		for (Iterator it = l.iterator(); it.hasNext();) {

			File f = (File) it.next();

			String fn = f + "";

			if (fn.matches(expr)) r.add(fn);

			if (isZip(f.getName())) {

				findZip(fn, new FileInputStream(f), new P() {

					public boolean accept(String t) {

						return t.matches(expr);

					}

				}, r);

			}

		}



		for (Iterator it = r.iterator(); it.hasNext();) {

			System.out.println(it.next());

		}

	}



	static void findFile(File f, P p, List r) {

		if (f.isDirectory()) {

			File[] files = f.listFiles();

			for (int i = 0; i < files.length; i++) findFile(files[i], p, r);

		} else if (p.accept(f + "")) {

			r.add(f);

		}

	}



	static void findZip(String f, InputStream in, P p, List r) throws IOException {

		ZipInputStream zin = new ZipInputStream(in);



		ZipEntry en;

		while ((en = zin.getNextEntry()) != null) {

			if (p.accept(en.getName())) r.add(f + "!" + en);

			if (isZip(en.getName())) findZip(f + "!" + en, zin, p, r);

		}

	}



	static String[] ZIP_EXTENSIONS = { ".zip", ".jar", ".war", ".ear" };



	static boolean isZip(String t) {

		for (int i = 0; i < ZIP_EXTENSIONS.length; i++) {

			if (t.endsWith(ZIP_EXTENSIONS[i])) {

				return true;

			}

		}

		return false;

	}



	static interface P {

		public boolean accept(String t);

	}

}

Files are not properly closed! Don't use this class in a long running application or properly close all streams.