Cache lazy loading in Java caching technology

Cache lazy loading in Java caching technology

In the Java circle, caching technology is a very common technology. The purpose of caching is to improve the performance of data access and avoid repeated calculations and repeated requests. Caching technology has a wide range of application scenarios, especially in applications that require frequent access to data, such as e-commerce websites, news portals, social applications, etc.

However, caching technology also has some disadvantages, such as: cache initialization and update may consume a lot of time and performance resources. Therefore, in order to improve the performance and efficiency of cache, a technology called "cache lazy loading" has emerged, which can effectively solve the problem of cache initialization and update, thereby improving system performance and efficiency.

What is cache lazy loading?

Cache lazy loading means delaying the initialization of cached data and waiting for the first access before loading the data into the cache. The advantage of this technology is that it can avoid unnecessary initialization and update operations, thereby reducing system overhead and resource consumption. Of course, the disadvantage of cache lazy loading is that it may cause some delay during the first access, but in most application scenarios, this delay is acceptable. Therefore, cache lazy loading technology is a very common technology in many applications.

How to implement cache lazy loading

In Java, there are many ways to implement cache lazy loading. Here we introduce several common implementation methods.

Method 1: Use ConcurrentHashMap and Future to implement

ConcurrentHashMap is a thread-safe hash table introduced in JDK 1.5, which can be used to store cached data, while Future can be used to load data asynchronously.

The specific implementation method is as follows:

public class MyCache {
    private final Map<String, Future<String>> cache = new ConcurrentHashMap<>();
    private final Function<String, String> loadDataFunction;

    public MyCache(Function<String, String> loadDataFunction) {
        this.loadDataFunction = loadDataFunction;
    }

    public String getData(String key) throws ExecutionException, InterruptedException {
        Future<String> future = cache.get(key);

        if (future == null) {
            Callable<String> callable = () -> loadDataFunction.apply(key);
            FutureTask<String> futureTask = new FutureTask<>(callable);
            future = cache.putIfAbsent(key, futureTask);  
            if (future == null) {
                future = futureTask;
                futureTask.run();
            }
        }
        return future.get();
    }
}

This implementation method is relatively simple, and the general process is as follows:

1. Try to obtain the Future value of the specified key from the cache;
2. If the Future value is null, it means that the corresponding data has not been cached, load the data through loadDataFunction, encapsulate it into a FutureTask object, and insert it into the cache;
3. If the insertion is successful (that is, before If no other thread has inserted the key), run the FutureTask to load the data asynchronously;
4. Finally, return the Future value corresponding to the specified key in the cache.

Method 2: Use Double-Checked Locking to achieve

Double-Checked Locking is a common multi-threaded programming technique that can avoid repeated lock competition and thus improve system performance. In cache lazy loading, you can use the Double-Checked Locking technique to achieve the effect of delayed initialization.

The specific implementation method is as follows:

public class MyCache {
    private Map<String, String> cache = null;

    public String getData(String key) {
        String data = cache.get(key);
        if (data == null) {
            synchronized (this) {
                data = cache.get(key);

                if (data == null) {
                    data = loadData(key);
                    cache.put(key, data);
                }
            }
        }
        return data;
    }

    private String loadData(String key) {
        // TODO: load data from database or remote API
        return "data";
    }
}

This implementation method is relatively simple, and the general process is as follows:

1. Try to obtain the value of the specified key from the cache;
2. If the value is null, execute the synchronized code block;
3. In the synchronized code block, try to obtain the cached data again. If it is still null, call the loadData method to load the data and store it in In cache;
4. Finally, return the data corresponding to the specified key.

Method 3: Use AtomicReference to implement

AtomicReference is an atomic operation class introduced in JDK 1.5, which can be used to achieve the effect of cached lazy loading.

The specific implementation method is as follows:

public class MyCache {
    private final Map<String, String> cache = new ConcurrentHashMap<>();
    private final AtomicReference<Map<String, String>> reference =
            new AtomicReference<>(null);

    public String getData(String key) {
        Map<String, String> currentCache = reference.get();

        if (currentCache == null) {
            currentCache = cache;
            reference.compareAndSet(null, currentCache);
        }

        return currentCache.computeIfAbsent(key, k -> loadData(k));
    }

    private String loadData(String key) {
        // TODO: load data from database or remote API
        return "data";
    }
}

This implementation method is relatively complicated. The approximate process is as follows:

1. Try to read the cache data pointed to by the reference;
2. If the cached data is null, read the data from ConcurrentHashMap and store it in AtomicReference as original data;
3. Then, use the computeIfAbsent method to obtain the data corresponding to the specified key from the cached data;
4. If the data corresponding to the specified key does not exist, call the loadData method to load the data, store it in the cache data, and return the data.

What are the benefits of using cached lazy loading?

Using cache lazy loading technology can bring the following benefits:

1. Reduce initialization and update overhead and resource consumption;
2. Avoid useless calculations and requests Operation;
3. Improve the response speed and throughput of the system;
4. Reduce the memory usage and overhead of the system;
5. Improve the maintainability and scalability of the system.

Summary

In Java caching technology, cache lazy loading is a very practical technology. By delaying initialization of cached data, unnecessary calculations and request operations can be avoided, improving system performance and efficiency. This article introduces several common cache lazy loading implementation methods, hoping to help everyone understand and master Java caching technology more deeply.

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