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In this article Xiaobian introduces in detail "Java singleton mode how to use HashMap to cache data", the content is detailed, the steps are clear, and the details are handled properly. I hope this "Java singleton mode how to cache data using HashMap" article can help you solve your doubts.

1. What is the singleton model?

Singleton pattern is an object creation pattern, which is used to produce a concrete instance of an object, which ensures that only one instance is produced by a class in the system. The singleton implemented in Java is the scope of a virtual machine, because the function of loading a class is a virtual machine, so a virtual machine creates an instance of the class when it implements the singleton class through its own ClassLoad loading. In the Java language, such behavior brings two major benefits:

1. For frequently used objects, the time it takes to create objects can be omitted, which is a considerable overhead for those heavyweight objects.

two。 Due to the reduction in the number of new operations, the frequency of use of system memory will also be reduced, which will reduce GC pressure and shorten GC pause time.

Therefore, for the key components and frequently used objects of the system, the use of singleton pattern can effectively improve the performance of the system. The core of the singleton pattern is to return a unique object instance through an interface. The first problem is to take back the permission to create an instance, let the class itself be responsible for creating an instance of its own class, and then let this class provide an external method that can access the instance of the class.

Second, the singleton mode combined with HashMap to achieve cache

1. Test result

two。 The code is as follows

JavaBean

Public class People {private String name; private int age; public String getName () {return name;} public void setName (String name) {this.name = name;} public int getAge () {return age;} public void setAge (int age) {this.age = age } @ Override public String toString () {return "People {" + "name='" + name +'\'+ ", age=" + age +'}';}}

Caching utility class

Import java.util.HashMap;import java.util.Map;public class CacheSingletonUtil {private static volatile CacheSingletonUtil cacheSingletonUtil; private static Map cacheSingletonMap; public static final String PEOPLE_LIST_KEY = "peopleList"; private CacheSingletonUtil () {cacheSingletonMap = new HashMap () } / * * there are two types of singleton mode * lazy type: create the singleton class object only when you really need to use it * hungry Han style: the singleton object has been created when the class is loaded Wait for the program to use * / / lazy singleton mode public static CacheSingletonUtil getInstance () {if (cacheSingletonUtil = = null) {/ / Thread An and Thread B to see cacheSingletonUtil = null at the same time, if not null Then directly return cacheSingletonUtil synchronized (CacheSingletonUtil.class) {/ / thread An or thread B to obtain the lock to initialize if (cacheSingletonUtil = = null) {/ / one of the threads enters the branch, while the other thread does not enter the branch cacheSingletonUtil = new CacheSingletonUtil () } return cacheSingletonUtil;} / * add to memory * / public void addCacheData (String key,Object obj) {cacheSingletonMap.put (key,obj);} / * remove * / public Object getCacheData (String key) {return cacheSingletonMap.get (key) from memory } / * clear * / public void removeCacheData (String key) {cacheSingletonMap.remove (key);}} from memory

Test class

Import org.apache.commons.collections.CollectionUtils;import java.util.ArrayList;import java.util.List;public class CacheSingletonTest {public static void main (String [] args) {/ / Test query testQuery ();} private static void testQuery () {System.out.println ("first query starts"); query (); System.out.println ("first query ends") System.out.println ("="); System.out.println ("second query starts"); query (); System.out.println ("second query ends");} / * * query data * / private static List query () {List peopleList = null; List cacheData = (List) CacheSingletonUtil.getInstance () .getCacheData (CacheSingletonUtil.PEOPLE_LIST_KEY) If (CollectionUtils.isNotEmpty (cacheData)) {System.out.println ("read from memory"); peopleList = cacheData;} else {System.out.println ("read from database"); peopleList = getData (); / / add to memory CacheSingletonUtil.getInstance () .addCacheData (CacheSingletonUtil.PEOPLE_LIST_KEY, peopleList) } for (People people: peopleList) {System.out.println ("name:" + people.getName () + "age:" + people.getAge ());} return peopleList;} / * * Delete data * / private void deleteCache () {CacheSingletonUtil.getInstance () .removeCacheData (CacheSingletonUtil.PEOPLE_LIST_KEY) } private static List getData () {People p1 = new People (); p1.setName ("Jack"); p1.setAge (25); People p2 = new People (); p2.setName ("Brown"); p2.setAge (28); List peopleList = new ArrayList (); peopleList.add (p1); peopleList.add (p2); return peopleList }} after reading this, the article "how to cache data with HashMap in Java singleton mode" has been introduced. If you want to master the knowledge points of this article, you still need to practice and use it yourself. If you want to know more about related articles, please follow the industry information channel.

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