android 轻松避免内存溢出

package l.test1.util; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.util.HashMap; import java.util.HashSet; import java.util.LinkedList; import java.util.Map; import java.util.Queue; import java.util.Set; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.BitmapFactory.Options; /** * Bitmap工具类,缓存用过的指定数量的图片,使用此工具类,不再需要手动管理Bitmap内存 原理: * 用一个队列保存使用Bitmap的顺序,每次使用Bitmap将对象移动到队列头 当内存不够,或者达到制定的缓存数量的时候,回收队列尾部图片 * 保证当前使用最多的图片得到最长时间的缓存,提高速度 * * @author liaoxingliao * */ public final class BitMapUtil { private static final Size ZERO_SIZE = new Size(0, 0); private static final Options OPTIONS_GET_SIZE = new Options(); private static final Options OPTIONS_DECODE = new Options(); private static final byte[] LOCKED = new byte[0]; private static final LinkedList<String> CACHE_ENTRIES = new LinkedList<String>(); // 此对象用来保持Bitmap的回收顺序,保证最后使用的图片被回收 private static final Queue<QueueEntry> TASK_QUEUE = new LinkedList<QueueEntry>(); // 线程请求创建图片的队列 private static final Set<String> TASK_QUEUE_INDEX = new HashSet<String>(); // 保存队列中正在处理的图片的key,有效防止重复添加到请求创建队列 private static final Map<String, Bitmap> IMG_CACHE_INDEX = new HashMap<String, Bitmap>(); // 缓存Bitmap // 通过图片路径,图片大小 private static int CACHE_SIZE = 200; // 缓存图片数量 static { OPTIONS_GET_SIZE.inJustDecodeBounds = true; // 初始化创建图片线程,并等待处理 new Thread() { { setDaemon(true); } public void run() { while (true) { synchronized (TASK_QUEUE) { if (TASK_QUEUE.isEmpty()) { try { TASK_QUEUE.wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } QueueEntry entry = TASK_QUEUE.poll(); String key = createKey(entry.path, entry.width, entry.height); TASK_QUEUE_INDEX.remove(key); createBitmap(entry.path, entry.width, entry.height); } } }.start(); } /** * 创建一张图片 如果缓存中已经存在,则返回缓存中的图,否则创建一个新的对象,并加入缓存 * 宽度,高度,为了缩放原图减少内存的,如果输入的宽,高,比原图大,返回原图 * * @param path 图片物理路径 (必须是本地路径,不能是网络路径) * @param width 需要的宽度 * @param height 需要的高度 * @return */ public static Bitmap getBitmap(String path, int width, int height) { Bitmap bitMap = null; try { if (CACHE_ENTRIES.size() >= CACHE_SIZE) { destoryLast(); } bitMap = useBitmap(path, width, height); if (bitMap != null && !bitMap.isRecycled()) { return bitMap; } bitMap = createBitmap(path, width, height); String key = createKey(path, width, height); synchronized (LOCKED) { IMG_CACHE_INDEX.put(key, bitMap); CACHE_ENTRIES.addFirst(key); } } catch (OutOfMemoryError err) { destoryLast(); System.out.println(CACHE_SIZE); return createBitmap(path, width, height); } return bitMap; } /** * 设置缓存图片数量 如果输入负数,会产生异常 * * @param size */ public static void setCacheSize(int size) { if (size <= 0) { throw new RuntimeException("size :" + size); } while (size < CACHE_ENTRIES.size()) { destoryLast(); } CACHE_SIZE = size; } /** * 加入一个图片处理请求到图片创建队列 * * @param path * 图片路径(本地) * @param width * 图片宽度 * @param height * 图片高度 */ public static void addTask(String path, int width, int height) { QueueEntry entry = new QueueEntry(); entry.path = path; entry.width = width; entry.height = height; synchronized (TASK_QUEUE) { String key = createKey(path, width, height); if (!TASK_QUEUE_INDEX.contains(key) && !IMG_CACHE_INDEX.containsKey(key)) { TASK_QUEUE.add(entry); TASK_QUEUE_INDEX.add(key); TASK_QUEUE.notify(); } } } /** * 通过图片路径返回图片实际大小 * @param path 图片物理路径 * @return */ public static Size getBitMapSize(String path) { File file = new File(path); if (file.exists()) { InputStream in = null; try { in = new FileInputStream(file); BitmapFactory.decodeStream(in, null, OPTIONS_GET_SIZE); return new Size(OPTIONS_GET_SIZE.outWidth, OPTIONS_GET_SIZE.outHeight); } catch (FileNotFoundException e) { return ZERO_SIZE; } finally { closeInputStream(in); } } return ZERO_SIZE; } // ------------------------------------------------------------------ private Methods // 将图片加入队列头 private static Bitmap useBitmap(String path, int width, int height) { Bitmap bitMap = null; String key = createKey(path, width, height); synchronized (LOCKED) { bitMap = IMG_CACHE_INDEX.get(key); if (null != bitMap) { if (CACHE_ENTRIES.remove(key)) { CACHE_ENTRIES.addFirst(key); } } } return bitMap; } // 回收最后一张图片 private static void destoryLast() { synchronized (LOCKED) { String key = CACHE_ENTRIES.removeLast(); if (key.length() > 0) { Bitmap bitMap = IMG_CACHE_INDEX.remove(key); if (bitMap != null && !bitMap.isRecycled()) { bitMap.recycle(); bitMap = null; } } } } // 创建键 private static String createKey(String path, int width, int height) { if (null == path || path.length() == 0) { return ""; } return path + "_" + width + "_" + height; } // 通过图片路径,宽度高度创建一个Bitmap对象 private static Bitmap createBitmap(String path, int width, int height) { File file = new File(path); if (file.exists()) { InputStream in = null; try { in = new FileInputStream(file); Size size = getBitMapSize(path); if (size.equals(ZERO_SIZE)) { return null; } int scale = 1; int a = size.getWidth() / width; int b = size.getHeight() / height; scale = Math.max(a, b); synchronized (OPTIONS_DECODE) { OPTIONS_DECODE.inSampleSize = scale; Bitmap bitMap = BitmapFactory.decodeStream(in, null, OPTIONS_DECODE); return bitMap; } } catch (FileNotFoundException e) { e.printStackTrace(); } finally { closeInputStream(in); } } return null; } // 关闭输入流 private static void closeInputStream(InputStream in) { if (null != in) { try { in.close(); } catch (IOException e) { e.printStackTrace(); } } } // 图片大小 static class Size { private int width, height; Size(int width, int height) { this.width = width; this.height = height; } public int getWidth() { return width; } public int getHeight() { return height; } } // 队列缓存参数对象 static class QueueEntry { public String path; public int width; public int height; } }