设计模式

代理模式

• 通过引入一个代理对象来实现对目标对象的功能增强，Spring Aop就是动态代理
• 相关文章：juejin.cn/post/743643…

单例模式

懒加载

public class Singleton {
    private static Singleton singleton;
    
    private Singleton() {}
    
    public static synchronized Singleton getInstance() {
        if (singleton == null) {
            singleton = new Singleton();
        }
        return singleton;
    }
}

立即加载

public class Singleton {  
    private static Singleton instance = new Singleton();
    
    private Singleton (){}  
    
    public static Singleton getInstance() {  
    	return instance;  
    }  
}

责任链模式

• 将处理某个请求的对象通过数组或链表串联在一起，让这些对象依次处理这个请求

• 过滤敏感词案例：

  public class ApplicationDemo {
      public static void main(String[] args) {
          FilterChain chain = new FilterChain();
          chain.addFilter(new SexyFilter());
          chain.addFilter(new AdsFilter());
  
          boolean legal = filterChain.doFilter(new Content());
          if (!legal) {
              // 不发表
          } else {
              // 发表
          }
      }
  }
  

  public class FilterChain {
      private List<SensitiveFilter> filters = new ArrayList<>();
  
      public void addFilter(SensitiveFilter filter) {
          this.filters.add(filter);
      }
  
      // return true if content doesn't contain sensitive words.
      public boolean doFilter(Content content) {
          for (SensitiveFilter filter : filters) {
              if (!filter.doFilter(content)) {
                  return false;
              }
          }
          return true;
      }
  }
  

  public interface SensitiveFilter {
      boolean doFilter(Content content);
  }
  
  public class SexyFilter implements SensitiveFilter {
      @Override
      public boolean doFilter(Content content) {
          boolean legal = true;
          //...
          return legal;
      }
  }
  
  public class AdsFilter implements SensitiveFilter {
      @Override
      public boolean doFilter(Content content) {
          boolean legal = true;
          //...
          return legal;
      }
  }