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Redis是一个基于Key-value结构的Nosql数据库，它支持各种常见的数据结构以及非常方便的操作，
与其说它是一个数据库，不如说它是一个保存各种数据结构的服务器。今天闲来没事，用
Java集合类
实现了Redis的一些基本功能，算是温习下Java了。
1.Redis入门
Redis的Key键值为字符串，但是Value值支持许多种类型，如String字符串，List链表，Set无序集合，
SortedSet有序集合，甚至是Hash表。
各种数据结构通过不同的存取方法来区分。如Set/Get直接将值存为String，LPush/LPop/LRange将
值存到一个链表中，SAdd/ZAdd则区分了无序和有序集合。
下面我们来看下在Java中使用基本的集合类如何实现这些简单而方便的操作。
2.Java版的Redis
代码的组织结构如下图：
(); else list = serializer.unmarshal(list); LinkedList listRef = (LinkedList) list; for (Object value : values) listRef.addFirst(value); persistence.put(key, serializer.marshal(list)); } public void RPush(String key, Object... values) { Object list = persistence.get(key); if (list == null) list = new LinkedList(); else list = serializer.unmarshal(list); LinkedList listRef = (LinkedList) list; for (Object value : values) listRef.addLast(value); persistence.put(key, serializer.marshal(list)); } public Object[] LRange(String key, int start, int end) { Object list = persistence.get(key); if (list == null) return NULL; LinkedList listRef = (LinkedList) serializer.unmarshal(list); if (end > listRef.size()) end = listRef.size(); return listRef.subList(start, end).toArray(); } // ================================================= // Unsorted Set value // ================================================= public void SAdd(String key, Object... values) { Object set = persistence.get(key); if (set == null) set = new HashSet(); else set = serializer.unmarshal(set); HashSet setRef = (HashSet) set; for (Object value : values) setRef.add(value); persistence.put(key, serializer.marshal(set)); } public Object[] SMembers(String key) { Object set = persistence.get(key); if (set == null) return NULL; set = serializer.unmarshal(set); return ((HashSet) set).toArray(); } public Object[] SInter(String key1, String key2) { Object set1 = persistence.get(key1); Object set2 = persistence.get(key2); if (set1 == null || set2 == null) return NULL; HashSet set1Ref = (HashSet) serializer.unmarshal(set1); HashSet set2Ref = (HashSet) serializer.unmarshal(set2); set1Ref.retainAll(set2Ref); return set1Ref.toArray(); } public Object[] SDiff(String key1, String key2) { Object set1 = persistence.get(key1); Object set2 = persistence.get(key2); if (set1 == null || set2 == null) return NULL; HashSet set1Ref = (HashSet) serializer.unmarshal(set1); HashSet set2Ref = (HashSet) serializer.unmarshal(set2); set1Ref.removeAll(set2Ref); return set1Ref.toArray(); } // ================================================= // Sorted Set value // ================================================= public void ZAdd(String key, Object... values) { Object set = persistence.get(key); if (set == null) set = new TreeSet(); else set = serializer.unmarshal(set); TreeSet setRef = (TreeSet) set; for (Object value : values) setRef.add(value); persistence.put(key, serializer.marshal(set)); } public Object[] SRange(String key, Object from) { Object set = persistence.get(key); if (set == null) return NULL; set = serializer.unmarshal(set); return ((TreeSet) set).tailSet(from).toArray(); } } package com.cdai.studio.redis; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; import java.util.Arrays; class Serializer { Object marshal(Object object) { if (object == null) return null; return new BytesWrapper((Serializable) object); } Object unmarshal(Object object) { if (object == null) return null; return ((BytesWrapper) object).readObject(); } } class BytesWrapper { private byte[] bytes; BytesWrapper(T object) { writeBytes(object); } void writeBytes(T object) { try { ByteArrayOutputStream buffer = new ByteArrayOutputStream(); ObjectOutputStream output = new ObjectOutputStream(buffer); output.writeObject(object); output.flush(); bytes = buffer.toByteArray(); output.close(); } catch (IOException e) { e.printStackTrace(); throw new IllegalStateException(e); } } Object readObject() { try { ObjectInputStream input = new ObjectInputStream(new ByteArrayInputStream(bytes)); Object object = input.readObject(); input.close(); return object; } catch (Exception e) { e.printStackTrace(); throw new IllegalStateException(e); } } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + Arrays.hashCode(bytes); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; BytesWrapper other = (BytesWrapper) obj; if (!Arrays.equals(bytes, other.bytes)) return false; return true; } } package com.cdai.studio.redis; import java.util.HashMap; class Persistence { private HashMap storage = new HashMap(); void put(String key, Object value) { storage.put(key, value); } Object get(String key) { return storage.get(key); } }
3.简单的客户端
request = (List) input.readObject(); Object response = null; if ("Set".equals(request.get(0))) { redis.Set((String) request.get(1), request.get(2)); } else if ("Get".equals(request.get(0))) { response = redis.Get((String) request.get(1)); } ObjectOutputStream output = new ObjectOutputStream(socket.getOutputStream()); output.writeObject(response); input.close(); output.close(); socket.close(); } } catch (Exception e) { e.printStackTrace(); } finally { if (serverSocket != null) { try { serverSocket.close(); } catch (IOException e) { } } } } } package com.cdai.studio.redis; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; import java.net.Socket; import java.util.Arrays; import java.util.List; public class RedisClient { public void Set(String key, Object value) { sendRequest(Arrays.asList("Set", key, value)); } public Object Get(String key) { return sendRequest(Arrays.asList("Get", key)); } private Object sendRequest(List payload) { Socket socket = null; try { socket = new Socket("localhost", 1234); ObjectOutputStream output = new ObjectOutputStream(socket.getOutputStream()); output.writeObject(payload); output.flush(); ObjectInputStream input = new ObjectInputStream(socket.getInputStream()); Object response = input.readObject(); output.close(); input.close(); return response; } catch (Exception e) { e.printStackTrace(); } finally { if (socket != null) { try { socket.close(); } catch (Exception e) { } } } return null; } }
4.实现简单的Twitter
5.需要注意的问题
byte数组的equals和hashcode默认实现比较对象地址的，要借助于Arrays的equals和hashcode方法。
String字符串序列化和反序列化时要注意编码格式的问题，编码解码时应该使用相同的编码。
HashSet上的操作，removeAll补集，retainAll交集，addAll并集。
6.更加强大的Redis
Redis自己实现了各种数据结构，可以非常方便地增删改查，并且效率很高。这里我们只是用
Java来简单的学习了下Redis基本功能，其实Redis还支持很多其他的高级功能，
如消息订阅、
数据过期设置、事务、数据持久化。想要进一步学习的话可以试着用Java实现它们。
