How Can the Strategy Pattern Optimize File Encryption Based on File Size?

Practical application of strategy mode in file encryption

Strategy pattern allows developers to build applications that adapt to changing needs without modifying core functionality. To illustrate this concept, let’s explore a practical example that goes beyond an order validation scenario.

A real application scenario is file encryption. When encrypting files, the choice of encryption strategy should depend on the file size. For small files, an in-memory approach is possible, where the entire file is loaded into memory for processing. However, for large files, this approach may not be practical due to memory limitations.

To solve this problem, a policy mode can be implemented that provides two encryption strategies: one for small files operated in memory, and another for large files that utilize part of the memory and temporary file storage. Client code does not need to know these implementation details and only needs to interact with the common cryptographic interface.

Consider the following simplified code example:

<code class="language-java">File file = getFile();
Cipher c = CipherFactory.getCipher(file.size());
c.encrypt();

interface Cipher {
    void encrypt();
}

class InMemoryCipher implements Cipher {
    @Override
    public void encrypt() {
        // 将文件加载到内存并加密
    }
}

class DiskCipher implements Cipher {
    @Override
    public void encrypt() {
        // 分块加密文件，并将结果存储在临时文件中
    }
}</code>

In this example, CipherFactory determines the appropriate strategy based on the file size and returns the corresponding implementation. Client code does not need to worry about the underlying implementation when performing cryptographic operations. This logical separation promotes flexibility, allowing the system to adapt seamlessly to future changes or new encryption algorithms.

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