├── ConsistentHashRouter.java
├── PhysicalNode.java
├── README.md
└── VirtualNode.java


/ConsistentHashRouter.java:
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 1 | package com.moe.oa.util.hash;
 2 | 
 3 | import java.security.MessageDigest;
 4 | import java.security.NoSuchAlgorithmException;
 5 | import java.util.Collection;
 6 | import java.util.Iterator;
 7 | import java.util.SortedMap;
 8 | import java.util.TreeMap;
 9 | 
10 | import com.moe.oa.model.VirtualNode;
11 | import com.moe.oa.model.PhysicalNode;
12 | /**
13 |  * 
14 |  * @author songwenjun
15 |  *
16 |  */
17 | public class ConsistentHashRouter{
18 | 	private SortedMap<Long,VirtualNode> ring = new TreeMap<Long,VirtualNode>();	
19 | 	private MD5Hash hashfunction = new MD5Hash();	
20 | 
21 | 	public ConsistentHashRouter(Collection<PhysicalNode> pNodes, int vnodeCount) {
22 | 		for (PhysicalNode pNode : pNodes) {
23 | 			addNode(pNode,vnodeCount);
24 | 		}
25 | 	}
26 | 	
27 | 	public void addNode(PhysicalNode pNode, int vnodeCount){
28 | 		int existingReplicas = getReplicas(pNode.toString());
29 | 		for(int i=0;i<vnodeCount;i++){
30 | 			VirtualNode vNode= new VirtualNode(pNode,i+existingReplicas);
31 | 			ring.put(hashfunction.hash(vNode.toString()), vNode);
32 | 		}
33 | 	}
34 | 	
35 |     public void removeNode(PhysicalNode pNode) {
36 |         Iterator<Long> it = ring.keySet().iterator();
37 |         while (it.hasNext()) {
38 |             Long key = it.next();
39 |             VirtualNode virtualNode = ring.get(key);
40 |             if (virtualNode.matches(pNode.toString())) {
41 |                 it.remove();
42 |             }
43 |         }
44 |     }
45 |     
46 |     public PhysicalNode getNode(String key){
47 |         if (ring.isEmpty()) {
48 |             return null;
49 |         }
50 |     	Long hashKey=hashfunction.hash(key);
51 |     	SortedMap<Long,VirtualNode> tailMap= ring.tailMap(hashKey);
52 | 		hashKey = tailMap!=null&&!tailMap.isEmpty() ?tailMap.firstKey():ring.firstKey();
53 | 		return ring.get(hashKey).getParent();	
54 |     }
55 | 	
56 |     public int getReplicas(String nodeName) {
57 |         int replicas = 0;
58 |         for (VirtualNode node : ring.values()) {
59 |             if (node.matches(nodeName)) {
60 |                 replicas++;
61 |             }
62 |         }
63 |         return replicas;
64 |     }
65 |     
66 | 	private static class MD5Hash {
67 | 		MessageDigest instance;
68 | 
69 | 		public MD5Hash() {
70 | 			try {
71 | 				instance = MessageDigest.getInstance("MD5");
72 | 			} catch (NoSuchAlgorithmException e) {
73 | 			}
74 | 		}
75 | 		
76 | 		long hash(String key) {
77 | 			instance.reset();
78 | 			instance.update(key.getBytes());
79 | 			byte[] digest = instance.digest();
80 | 
81 | 			long h = 0;
82 | 			for (int i = 0; i < 4; i++) {
83 | 				h <<= 8;
84 | 				h |= ((int) digest[i]) & 0xFF;
85 | 			}
86 | 			return h;
87 | 		}
88 | 	};
89 | }
90 | 


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/PhysicalNode.java:
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 1 | package com.moe.oa.model;
 2 | /**
 3 |  * 
 4 |  * @author songwenjun
 5 |  *
 6 |  */
 7 | public class PhysicalNode {
 8 | 	private String domain;
 9 | 	private String ip;
10 | 	private int port;	
11 | 	 
12 | 	public PhysicalNode(String domain,String ip,int port){
13 | 		this.domain=domain;
14 | 		this.ip=ip;
15 | 		this.port=port;
16 | 	}
17 | 	
18 | 	@Override
19 | 	public String toString() {
20 | 		return domain+":"+ ip+":"+ port ;
21 | 	}
22 | 
23 | 	public String getDomain() {
24 | 		return domain;
25 | 	}
26 | 	public void setDomain(String domain) {
27 | 		this.domain = domain;
28 | 	}
29 | 	public String getIp() {
30 | 		return ip;
31 | 	}
32 | 	public void setIp(String ip) {
33 | 		this.ip = ip;
34 | 	}
35 | 	public int getPort() {
36 | 		return port;
37 | 	}
38 | 	public void setPort(int port) {
39 | 		this.port = port;
40 | 	}
41 | }
42 | 


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/README.md:
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1 | ConsistentHash
2 | ==============
3 | 
4 | Implementing Consistent Hashing in Java
5 | 
6 | Reference
7 | http://www.codeproject.com/Articles/56138/Consistent-hashing
8 | 


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/VirtualNode.java:
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 1 | package com.moe.oa.model;
 2 | /**
 3 |  * 
 4 |  * @author songwenjun
 5 |  *
 6 |  */
 7 | public class VirtualNode {   
 8 |     private int replicaNumber;  
 9 |     private PhysicalNode parent;
10 | 
11 | 	public VirtualNode(PhysicalNode parent, int replicaNumber) {    	
12 |         this.replicaNumber = replicaNumber; 
13 |         this.parent = parent;
14 |     }
15 | 
16 |     public boolean matches(String host) {
17 |         return parent.toString().equalsIgnoreCase(host);
18 |     }	
19 | 
20 | 	@Override
21 |     public String toString() {
22 |         return parent.toString().toLowerCase() + ":" + replicaNumber;
23 |     }
24 | 
25 | 	public int getReplicaNumber() {
26 | 		return replicaNumber;
27 | 	}
28 | 
29 | 	public void setReplicaNumber(int replicaNumber) {
30 | 		this.replicaNumber = replicaNumber;
31 | 	}	
32 | 
33 |     public PhysicalNode getParent() {
34 | 		return parent;
35 | 	}
36 | }
37 | 


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