Java版的Redis

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：

 package com.cdai.studio.redis;

 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.TreeSet;

 @SuppressWarnings("unchecked")
 public class RedisDB {

     private Persistence persistence = new Persistence();

     private Serializer serializer = new Serializer();

     private static final Object[] NULL = new Object[0];


     // =================================================
     //                  String value
     // =================================================

     public void Set(String key, Object value) {
         persistence.put(key, serializer.marshal(value));
     }

     public Object Get(String key) {
         return serializer.unmarshal(persistence.get(key));
     }

     public Object[] MGet(String... keys) {
         Object[] values = new Object[keys.length];
         for (int i = 0; i < keys.length; i++)
             values[i] = Get(keys[i]);
         return values;
     }

     public int Incr(String key) {
         Object value = Get(key);
         Integer valueRef = (value == null) ? 1 : (Integer) value;
         Set(key, valueRef + 1);
         return valueRef;
     }


     // =================================================
     //                  List value
     // =================================================

     public void LPush(String key, Object... values) {
         Object list = persistence.get(key);
         if (list == null)
             list = new LinkedList<Object>();
         else
             list = serializer.unmarshal(list);

         LinkedList<Object> listRef = (LinkedList<Object>) 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<Object>();
         else
             list = serializer.unmarshal(list);

         LinkedList<Object> listRef = (LinkedList<Object>) 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<Object> listRef = (LinkedList<Object>) 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<Object>();
         else
             set = serializer.unmarshal(set);

         HashSet<Object> setRef = (HashSet<Object>) 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<Object>) 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<Object> set1Ref = (HashSet<Object>) serializer.unmarshal(set1);
         HashSet<Object> set2Ref = (HashSet<Object>) 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<Object> set1Ref = (HashSet<Object>) serializer.unmarshal(set1);
         HashSet<Object> set2Ref = (HashSet<Object>) 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<Object>();
         else
             set = serializer.unmarshal(set);

         TreeSet<Object> setRef = (TreeSet<Object>) 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<Object>) 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;

     <T extends Serializable> BytesWrapper(T object) {
         writeBytes(object);
     }

     <T extends Serializable> 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<String, Object> storage =
         new HashMap<String, Object>();


     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

 package com.cdai.studio.redis;

 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.io.ObjectOutputStream;
 import java.net.ServerSocket;
 import java.net.Socket;
 import java.util.List;

 public class RedisServer {

     private RedisDB redis;

     public RedisServer(RedisDB redis) {
         this.redis = redis;
     }

     @SuppressWarnings("unchecked")
     public void start() {
         ServerSocket serverSocket = null;
         try {
             serverSocket = new ServerSocket(1234);
             while (true) {
                 Socket socket = serverSocket.accept();

                 ObjectInputStream input = new ObjectInputStream(socket.getInputStream());
                 List<Object> request = (List<Object>) 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 <T extends Serializable> void Set(String key, Object value) {
         sendRequest(Arrays.asList("Set", key, value));
     }

     public Object Get(String key) {
         return sendRequest(Arrays.<Object>asList("Get", key));
     }

     private Object sendRequest(List<Object> 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

 package com.cdai.studio.redis;

 import java.util.Arrays;

 public class RedisTest {

     public static void main(String[] args) {

         RedisDB redis = new RedisDB();

         // 1.Create user follow relationship
         redis.SAdd("users", "A", "B", "C");

         // User A follows B, C
         redis.SAdd("users:A:following", "B", "C");
         redis.SAdd("users:B:followers", "A");
         redis.SAdd("users:C:followers", "A");

         // User C follows B
         redis.SAdd("users:C:following", "B");
         redis.SAdd("users:B:followers", "C");


         // 2.1 B send tweet
         int tid = redis.Incr("tweets:next_id");
         redis.Set("tweets:" + tid, "B publish hello");
         redis.LPush("global:timeline", tid);
         redis.LPush("users:B:timeline", tid);
         for (Object follower : redis.SMembers("users:B:followers"))
             redis.LPush("users:" + follower + ":timeline", tid);

         // 2.2 C send tweet
         tid = redis.Incr("tweets:next_id");
         redis.Set("tweets:" + tid, "C publish world");
         redis.LPush("global:timeline", tid);
         redis.LPush("users:C:timeline", tid);
         for (Object follower : redis.SMembers("users:C:followers"))
             redis.LPush("users:" + follower + ":timeline", tid);


         Object[] tids = redis.LRange("global:timeline", 0, 9);
         String[] tweetids = new String[tids.length];
         for (int i = 0; i < tids.length; i++)
             tweetids[i] = "tweets:" + tids[i];
         System.out.println(Arrays.toString(redis.MGet(tweetids)));
     }

 }

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。