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public class Single {

    private static volatile Single INSTANCE;

    private Single(){}

    public static Single getInstance(){
        //first check object
        if(INSTANCE == null){
            //locks in the class dimension
            synchronized (Single.class){
                //second check object
                if(INSTANCE == null){
                    INSTANCE = new Single();
                }
            }
        }
        return INSTANCE;
    }
}

public class CacheAside<T, K> implements CacheUpdate<T, K>{
    private Map<K, T> map;

    @Override
    public T getData(K key) {
        //if cache has data, return
        return map.get(key);
    }

    @Override
    public boolean updateData(K key, T data) {
        map.remove(key, data);
        return true;
    }

    @Override
    public boolean addData(K key, T data) {
        return Objects.nonNull(map.put(key, data));
    }

    @Override
    public boolean removeData(K key) {
        map.remove(key);
        return true;
    }

    public CacheAside() {
        map = new HashMap<>();
    }
}

public class CacheAsideClient<T, K> implements CacheUpdateClient<T, K>{

    public CacheUpdateFactory<T, K> factory = CacheUpdateFactory.getInstance();

    private CacheUpdate<T, K> cacheUpdate;

    private DatabaseOperation<T, K> databaseOperation;

    @Override
    public T getData(K key){
        //get data from cache
        T dataFromCache = cacheUpdate.getData(key);
        //if cache haven't, get from database and put to cache
        if(Objects.nonNull(dataFromCache)){
            return dataFromCache;
        }
        T dataFromDatabase = databaseOperation.getData(key);
        cacheUpdate.addData(key, dataFromDatabase);
        return dataFromDatabase;
    }

    @Override
    public boolean updateData(K key, T data){
        //update data to database
        boolean updateToDatabaseRes = databaseOperation.updateData(key, data);
        if(updateToDatabaseRes){
            //invalid cache data
            return cacheUpdate.removeData(key);
        }
        return false;
    }

    @Override
    public boolean addData(K key, T data){
        //add data to database
        return databaseOperation.addData(key, data);
    }

    @Override
    public boolean removeData(K key){
        //remove from database
        boolean removeFromDatabaseRes = databaseOperation.removeData(key);
        if(removeFromDatabaseRes){
            //invalid cache data
            return cacheUpdate.removeData(key);
        }
        return false;
    }

    public CacheAsideClient() {
        cacheUpdate = factory.getObject(CacheUpdateEnum.CACHE_ASIDE);
        databaseOperation = (DatabaseOperation<T, K>) new MockDatabaseOperation<T>();
    }
}

public class ReadOrWriteThough<T, K> implements CacheUpdate<T, K>{

    private DatabaseOperation<T, K> databaseOperation;

    private Map<K, T> map;

    @Override
    public T getData(K key) {
        //if cache has data, return
        if(map.containsKey(key)){
            return map.get(key);
        }
        //get data from database and write to cache
        T data = databaseOperation.getData(key);
        map.put(key, data);
        return data;
    }

    @Override
    public boolean updateData(K key, T data) {
        map.put(key, data);
        return databaseOperation.updateData(key, data);
    }

    @Override
    public boolean addData(K key, T data) {
        map.put(key, data);
        return databaseOperation.addData(key, data);
    }

    @Override
    public boolean removeData(K key) {
        map.remove(key);
        return databaseOperation.removeData(key);
    }

    public ReadOrWriteThough() {
        databaseOperation = (DatabaseOperation<T, K>) new MockDatabaseOperation<>();
        map = new HashMap<>();
    }
}

public class ReadOrWriteThoughClient<T, K> implements CacheUpdateClient<T, K>{

    private CacheUpdateFactory<T, K> factory = CacheUpdateFactory.getInstance();

    private CacheUpdate<T, K> cacheUpdate;

    @Override
    public T getData(K key) {
        return cacheUpdate.getData(key);
    }

    @Override
    public boolean updateData(K key, T data) {
        return cacheUpdate.updateData(key, data);
    }

    @Override
    public boolean addData(K key, T data) {
        return cacheUpdate.addData(key, data);
    }

    @Override
    public boolean removeData(K key) {
        return cacheUpdate.removeData(key);
    }

    public ReadOrWriteThoughClient() {
        cacheUpdate = factory.getObject(CacheUpdateEnum.READ_WRITE_THOUGH);
    }
}

public class WriteBehind<T, K> implements CacheUpdate<T, K> {

    private Map<K, T> map;

    private DatabaseOperation<T, K> databaseOperation;

    private ThreadPoolExecutor threadPoolExecutor;

    @Override
    public T getData(K key) {
        if(map.containsKey(key)){
            return map.get(key);
        }
        T data = databaseOperation.getData(key);
        map.put(key, data);
        return data;
    }

    @Override
    public boolean updateData(K key, T data) {
        map.put(key, data);
        threadPoolExecutor.execute(() -> databaseOperation.updateData(key, data));
        return true;
    }

    @Override
    public boolean addData(K key, T data) {
        map.put(key, data);
        threadPoolExecutor.execute(() -> databaseOperation.addData(key, data));
        return true;
    }

    @Override
    public boolean removeData(K key) {
        map.remove(key);
        threadPoolExecutor.execute(() -> databaseOperation.removeData(key));
        return true;
    }

    public WriteBehind() {
        map = new HashMap<>();
        databaseOperation = (DatabaseOperation<T, K>) new MockDatabaseOperation<>();
        threadPoolExecutor = new ThreadPoolExecutor(5, 10, 1000, TimeUnit.SECONDS, new ArrayBlockingQueue<>(1000), new ThreadPoolExecutor.CallerRunsPolicy());
    }

}

public class WriteBehindClient<T, K> implements CacheUpdateClient<T, K>{

    private CacheUpdateFactory<T, K> cacheUpdateFactory = CacheUpdateFactory.getInstance();

    private CacheUpdate<T, K> cacheUpdate;

    @Override
    public T getData(K key) {
        return cacheUpdate.getData(key);
    }

    @Override
    public boolean updateData(K key, T data) {
        return cacheUpdate.updateData(key, data);
    }

    @Override
    public boolean addData(K key, T data) {
        return cacheUpdate.addData(key, data);
    }

    @Override
    public boolean removeData(K key) {
        return cacheUpdate.removeData(key);
    }

    public WriteBehindClient() {
        cacheUpdate = cacheUpdateFactory.getObject(CacheUpdateEnum.WRITE_BEHIND);
    }
}

package org.CommonAlgorithms.ConsistentHash;

import org.CommonAlgorithms.HashAlgorithm.HashService;
import java.util.List;

/**
 * consistentHashing interface
 * @author cartoon
 * @since  10/01/2021
 * @version 1.1
 */
public interface ConsistentHashing {

    /**
     * put data to hash loop
     * @param data data list
     * @return put result
     */
    boolean putData(List<String> data);

    /**
     * put data to hash loop
     * @param data data
     * @return put result
     */
    boolean putData(String data);

    /**
     * remove node from hash loop
     * @param node removing node
     * @return remove result
     */
    boolean removeNode(String node);

    /**
     * add node to hash loop
     * @param node adding node
     * @return add result
     */
    boolean addNode(String node);

    /**
     * inject hash method to hash loop
     * @param hashService hash method
     * @throws UnsupportedOperationException if loop already has node
     */
    void setHashMethod(HashService hashService);

    /**
     * print all data in loop according ascending hash value with nodes
     */
    void printAllData();

}

package org.CommonAlgorithms.ConsistentHash;

import org.CommonAlgorithms.HashAlgorithm.HashService;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.*;

/**
 * consistent hash achieve
 * @author cartoon
 * @since  2021/01/17
 */
public class ConsistentHashingImpl implements ConsistentHashing {

    private static final Logger log = LoggerFactory.getLogger(ConsistentHashingImpl.class);

    /**
     * virtual node name template
     */
    private static final String virtualNodeFormat = "%s&&%d";

    /**
     * real node and its virtual node mapping
     */
    private SortedMap<String, List<String>> realNodeToVirtualNode;

    /**
     * hash and its node mapping
     */
    private SortedMap<Integer, String> hashToNodes;

    /**
     * node and its data mapping
     */
    private Map<String, List<String>> nodeToData;

    /**
     * determine virtual node's number of each node
     */
    private int virtualNodeNum;

    /**
     * inject hash method, if null, use loop default hash method
     */
    private HashService hashService;


    public ConsistentHashingImpl() {
        this(0, new String[0]);
    }

    public ConsistentHashingImpl(String... nodes) {
        this(0, nodes);
    }

    public ConsistentHashingImpl(int virtualNodeNum) {
        this(virtualNodeNum, new String[0]);
    }

    public ConsistentHashingImpl(int virtualNodeNum, String... nodes) {
        //1. intercept virtual num smaller than 0
        if(virtualNodeNum < 0){
            log.error("virtual num is not allow smaller than 0");
            throw new IllegalArgumentException();
        }
        //2. initialize loop member attributes
        this.virtualNodeNum = virtualNodeNum;
        realNodeToVirtualNode = new TreeMap<>();
        hashToNodes = new TreeMap<>();
        nodeToData = new HashMap<>();
        for(String server : nodes){
            hashToNodes.put(getHash(server), server);
            nodeToData.put(server, new LinkedList<>());
        }
        //3. if virtual node number bigger than 0, add virtual node
        if(virtualNodeNum > 0){
            for(String server : nodes){
                addVirtualNode(server);
            }
        }
    }

    @Override
    public boolean putData(List<String> data) {
        //1. circulate call put data method to add data to loop
        for(String incomingData : data){
            if(!putData(incomingData)){
                return false;
            }
        }
        return true;
    }

    @Override
    public boolean putData(String data) {
        if(hashToNodes.isEmpty()){
            log.error("put data, usable server is empty");
            return false;
        }
        //1. calculate data's hash value
        int currentHash = getHash(data);
        //2. get usual node(node's hash value is bigger than data's hash value), if usual node list is empty, get first node in loop
        SortedMap<Integer, String> usableNodes = hashToNodes.tailMap(currentHash);
        String node = usableNodes.isEmpty() ? hashToNodes.get(hashToNodes.firstKey()) : usableNodes.get(usableNodes.firstKey());
        //3. add data to node
        List<String> dataList = nodeToData.get(node);
        dataList.add(data);
        log.info("put data, data {} is placed to server {}, hash: {}", data, node, currentHash);
        return true;
    }

    @Override
    public boolean removeNode(String node) {
        //1. calculate hash value of removing node
        int removeServerHash = getHash(node);
        if(!hashToNodes.containsKey(removeServerHash)){
            log.error("remove server, current server is not in server list, please check server ip");
            return false;
        }
        //2. get data from removing node
        List<String> removeServerData = nodeToData.get(node);
        //3. get removing node's virtual node data, remove all virtual node with removing node
        if(virtualNodeNum != 0){
            for(String virtualNode : realNodeToVirtualNode.get(node)){
                removeServerData.addAll(nodeToData.get(virtualNode));
                hashToNodes.remove(getHash(virtualNode));
                nodeToData.remove(virtualNode);
            }
        }
        //4. remove node from hash loop
        hashToNodes.remove(removeServerHash);
        nodeToData.remove(node);
        if(hashToNodes.size() == 0){
            log.info("remove server, after remove, server list is empty");
            return true;
        }
        //5. put data to loop by call put data method
        putData(removeServerData);
        log.info("remove server, remove server {} success", node);
        return true;
    }

    @Override
    public boolean addNode(String node) {
        //1, calculate adding node's hash value
        int addServerHash = getHash(node);
        //2. add node and migrate data
        if(hashToNodes.isEmpty()){
            //2.1 add node and its virtual node to loop directly when current loop is empty
            hashToNodes.put(addServerHash, node);
            nodeToData.put(node, new LinkedList<>());
            if(virtualNodeNum > 0){
                addVirtualNode(node);
            }
        } else{
            //2.2.1 get data to be migrated from loop
            SortedMap<Integer, String> greatServers = hashToNodes.tailMap(addServerHash);
            String greatServer = greatServers.isEmpty() ? hashToNodes.get(hashToNodes.firstKey()) : greatServers.get(greatServers.firstKey());
            List<String> firstGreatServerData = new LinkedList<>(nodeToData.get(greatServer));
            //2.2.2 add node and its virtual node to loop
            hashToNodes.put(addServerHash, node);
            nodeToData.put(greatServer, new LinkedList<>());
            nodeToData.put(node, new LinkedList<>());
            if(virtualNodeNum != 0){
                addVirtualNode(node);
            }
            //2.2.3 migrate 2.2.1 data to loop by call put data method
            putData(firstGreatServerData);
        }
        log.info("add server, server {} has been added", node);
        return true;
    }

    @Override
    public void printAllData() {
        nodeToData.forEach((server, data) -> log.info("server {} contains data {}", server, data));
    }

    @Override
    public void setHashMethod(HashService hashService) {
        if(!hashToNodes.isEmpty()){
            throw new UnsupportedOperationException();
        }
        this.hashService = hashService;
    }

    private void addVirtualNode(String realNode){
        if(virtualNodeNum > 0){
            List<String> virtualNodeList = new LinkedList<>();
            for(int cnt = 0; cnt < this.virtualNodeNum; cnt++){
                //1. generate virtual node name by default format
                String virtualNodeName = String.format(virtualNodeFormat, realNode, cnt);
                //2. calculate each virtual node's hash value
                int virtualNodeHash = getHash(virtualNodeName);
                //3. current node already exist in loop, continue
                if(hashToNodes.containsKey(virtualNodeHash)){
                    continue;
                }
                //4. add node to loop
                virtualNodeList.add(virtualNodeName);
                hashToNodes.put(virtualNodeHash, virtualNodeName);
                nodeToData.put(virtualNodeName, new LinkedList<>());
            }
            //5. map virtual node to real node
            realNodeToVirtualNode.put(realNode, virtualNodeList);
        }
    }


    private int getHash(String data){
        return hashService == null ? defaultGetHash(data) : hashService.getHash(data);
    }

    private int defaultGetHash(String data){
        int res = 0;
        for(char tempChar : data.toCharArray()){
            if(tempChar >= '0' && tempChar <= '9'){
                res += tempChar;
            }
        }
        return res;
    }
}

package ConsistentHash;

import org.CommonAlgorithms.ConsistentHash.ConsistentHashing;
import org.CommonAlgorithms.ConsistentHash.ConsistentHashingImpl;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author cartoon
 * @date 2020/12/27
 */
public class ConsistentHashingWithoutVirtualNodeTest {

    private static final Logger log = LoggerFactory.getLogger(ConsistentHashingWithoutVirtualNodeTest.class);

    private ConsistentHashing consistentHashing;

    private String[] servers;

    private String[] data;

    @Before
    public void before(){
        servers = new String[]{"000", "111", "222", "333", "555"};
        consistentHashing = new ConsistentHashingImpl(servers);
        data = new String[]{"000", "111", "222", "333", "555"};
    }

    @Test
    public void testConsistentHashing(){
        for(String str : data){
            Assert.assertTrue(consistentHashing.putData(str));
        }
        consistentHashing.removeNode("333");
        consistentHashing.addNode("444");
        consistentHashing.putData("444");
        consistentHashing.printAllData();
    }
}

package ConsistentHash;

import org.CommonAlgorithms.ConsistentHash.ConsistentHashing;
import org.CommonAlgorithms.ConsistentHash.ConsistentHashingImpl;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author cartoon
 * @date 2021/01/17
 */
public class ConsistentHashingWithVirtualNodeTest {

    private static final Logger log = LoggerFactory.getLogger(ConsistentHashingWithVirtualNodeTest.class);

    private ConsistentHashing consistentHashing;

    private String[] servers;

    private String[] data;

    @Before
    public void before(){
        servers = new String[]{"000", "111", "222", "333", "555"};
        consistentHashing = new ConsistentHashingImpl(3, servers);
        data = new String[]{"000", "111", "222", "333", "555"};
    }

    @Test
    public void testConsistentHashing(){
        for(String str : data){
            Assert.assertTrue(consistentHashing.putData(str));
        }
        consistentHashing.removeNode("333");
        consistentHashing.addNode("444");
        consistentHashing.putData("444");
        consistentHashing.putData("555&&0");
        consistentHashing.printAllData();
    }
}

@DisplayName("multipart get config")
@SpringBootTest
public class MultipartGetConfigTest {

    private static final Logger log = LoggerFactory.getLogger(MultipartGetConfigTest.class);

    @Autowired
    private ConfigByValueAnnotation configByValueAnnotation;

    @Test
    public void getByValueAnnotation(){
        log.info("get by @Value, value: {}", configByValueAnnotation.getServerPort());
    }
}

@Component
public class ConfigByEnvironment implements EnvironmentAware {

       private static final Logger log = LoggerFactory.getLogger(ConfigByEnvironment.class);
    
       private Environment environment;
    
       public Optional<String> get(String configKey){
           String config = environment.getProperty(configKey);
           return Objects.isNull(config) ? Optional.empty() : Optional.of(config);
       }
    
       public void get(String configKey, Consumer<String> consumer){
           Optional<String> config = get(configKey);
           if(!config.isPresent()){
               log.warn("application config, get config by key fail, key: {}", configKey);
           }
           config.ifPresent(consumer);
       }
    
       @Override
       public void setEnvironment(@NonNull Environment environment) {
           this.environment = environment;
       }
}

public enum ConfigByEnvironmentKey {

       SERVER_PORT("server.port", "server port");
    
       private String key;
    
       private String description;
    
       ConfigByEnvironmentKey(String key, String description) {
           this.key = key;
           this.description = description;
       }
    
       public String getKey() {
           return key;
       }
    
       public String getDescription() {
           return description;
       }
}