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;
<p>import java.util.HashSet;<br />
import java.util.LinkedList;<br />
import java.util.TreeSet;</p>
<p>@SuppressWarnings("unchecked")<br />
public class RedisDB {</p>
<pre><code>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();}
</code></pre>
<p>}<br />
package com.cdai.studio.redis;</p>
<p>import java.io.ByteArrayInputStream;<br />
import java.io.ByteArrayOutputStream;<br />
import java.io.IOException;<br />
import java.io.ObjectInputStream;<br />
import java.io.ObjectOutputStream;<br />
import java.io.Serializable;<br />
import java.util.Arrays;</p>
<p>class Serializer {</p>
<pre><code>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();
}
</code></pre>
<p>}</p>
<p>class BytesWrapper {</p>
<pre><code>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;
}
</code></pre>
<p>}package com.cdai.studio.redis;</p>
<p>import java.util.HashMap;</p>
<p>class Persistence {</p>
<pre><code>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);
}
</code></pre>
<p>}
3. 简单的客户端
package com.cdai.studio.redis;
<p>import java.io.IOException;<br />
import java.io.ObjectInputStream;<br />
import java.io.ObjectOutputStream;<br />
import java.net.ServerSocket;<br />
import java.net.Socket;<br />
import java.util.List;</p>
<p>public class RedisServer {</p>
<pre><code>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) {}}
}
}
</code></pre>
<p>}package com.cdai.studio.redis;</p>
<p>import java.io.ObjectInputStream;<br />
import java.io.ObjectOutputStream;<br />
import java.io.Serializable;<br />
import java.net.Socket;<br />
import java.util.Arrays;<br />
import java.util.List;</p>
<p>public class RedisClient {</p>
<pre><code>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;
}
</code></pre>
<p>}
4. 实现简单的 Twitter
package com.cdai.studio.redis;
<p>import java.util.Arrays;</p>
<p>public class RedisTest {</p>
<pre><code>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)));
}
</code></pre>
<p>}
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。