android異步加載圖片

自己寫的，發上來大家看看，基礎不是太好。

package com.android.lalala.net;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.WeakHashMap;

import org.apache.http.HttpStatus;

import com.android.lalala.util.lalalaApplication;

import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.widget.ImageView;

/**
 * 圖片下載與緩存 思路是，先查看內存，後檢查SDcard，沒有的話聯網進行下載。
 */
public class ImageLoader {
	private ImageView imageView = null;
	private String urlPath = "";
	private WeakHashMap<String, Bitmap> picsHashMap = null;
	private String urlHashCode = "";
	private String filePath = "";
	private Handler handler = null;
	private Bitmap handlerBitmap = null;

	/**
	 * 構造器
	 * 
	 * @param imageView
	 *            imageview對象
	 * @param urlPath
	 *            下載的url地址
	 * @param filePath
	 *            緩存文件夾名稱
	 */

	public ImageLoader(ImageView imageView, String urlPath, String filePath) {
		super();
		this.imageView = imageView;
		this.urlPath = urlPath;
		this.filePath = filePath;
		urlHashCode = String.valueOf(urlPath.hashCode());
		// 從application中獲取picHashMap對象
		picsHashMap = lalalaApplication.getInstance().getPicHashMap();
		handler = new Handler();
		new imageLoaderThread().start();
	}
	
	/**
	 * 圖片下載線程
	 */
	private class imageLoaderThread extends Thread {
		@Override
		public void run() {
			super.run();
			if (readFromRAM()) {
				return;
			}
			if (readFromSDcard()) {
				return;
			}
			httpDownload();
		}
	}

	/**
	 * 開始下載
	 */
	private void httpDownload() {
		try {
			URL url = new URL(urlPath);
			HttpURLConnection connection = (HttpURLConnection) url
					.openConnection();
			connection.setConnectTimeout(10 * 1000);
			if (connection.getResponseCode() == HttpStatus.SC_OK) {
				InputStream is = connection.getInputStream();
				Bitmap bitmap = BitmapFactory.decodeStream(is);
				setBitmap(bitmap);
				lalalaApplication.getInstance().getPicHashMap()
						.put(urlHashCode, bitmap);
				saveToSDcard(bitmap);
			}

		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/**
	 * 將bitmap保存至SD卡上
	 * 
	 * @param bitmap
	 *            bitmap
	 */
	private void saveToSDcard(Bitmap bitmap) {
		try {
			String fileName = filePath + "/" + urlHashCode + ".JPG";
		File file = new File(filePath);
		if (!file.exists()) {
			file.mkdir();
		}
			BufferedOutputStream outputStream = new BufferedOutputStream(
					new FileOutputStream(new File(fileName)));
			bitmap.compress(CompressFormat.JPEG, 100, outputStream);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		}

	}

	/**
	 * 從內存中讀取bitmap圖片數據
	 * 
	 * @return true內存中有數據 false 內存中無數據
	 */
	private boolean readFromRAM() {
		if (picsHashMap.containsKey(urlHashCode)) {
			Bitmap bitmap = picsHashMap.get(urlHashCode);
			setBitmap(bitmap);
			return true;
		}
		return false;
	}

	/**
	 * 從SD卡讀取圖片
	 * 
	 * @return trueSDcard中有數據 false SDcard中無數據
	 */
	private boolean readFromSDcard() {
		String fileName = filePath + "/" + urlHashCode + ".JPG";
		File file = new File(fileName);
		if (!file.exists()) {
			return false;
		} else {
			Bitmap bitmap = BitmapFactory.decodeFile(fileName);
			picsHashMap.put(urlHashCode, bitmap);
			setBitmap(bitmap);
			return true;
		}

	}

	/**
	 * 設置圖片
	 * 
	 * @param bitmap
	 *            圖片
	 */
	private void setBitmap(Bitmap bitmap) {
		this.handlerBitmap = bitmap;
		handler.post(new Runnable() {
			@Override
			public void run() {
				imageView.setImageBitmap(handlerBitmap);
			}
		});
	}



}