82 - 剖析Google Guava中用的设计模式（二）

2021-10-21  本文已影响0人  舍是境界

本文再来学习一下，Google Guava 中用到的几种经典设计模式：Builder 模式、Wrapper 模式，以及之前没讲过的 Immutable 模式。

Builder 模式在 Guava 中的应用

public class CacheDemo {
  public static void main(String[] args) {
    Cache<String, String> cache = CacheBuilder.newBuilder()
            .initialCapacity(100)
            .maximumSize(1000)
            .expireAfterWrite(10, TimeUnit.MINUTES)
            .build();
    cache.put("key1", "value1");
    String value = cache.getIfPresent("key1");
    System.out.println(value);
  }
}

public <K1 extends K, V1 extends V> Cache<K1, V1> build() {
  this.checkWeightWithWeigher();
  this.checkNonLoadingCache();
  return new LocalManualCache(this);
}
private void checkNonLoadingCache() {
  Preconditions.checkState(this.refreshNanos == -1L, "refreshAfterWrite requires a LoadingCache");
}
private void checkWeightWithWeigher() {
  if (this.weigher == null) {
    Preconditions.checkState(this.maximumWeight == -1L, "maximumWeight requires weigher");
  } else if (this.strictParsing) {
    Preconditions.checkState(this.maximumWeight != -1L, "weigher requires maximumWeight");
  } else if (this.maximumWeight == -1L) {
    logger.log(Level.WARNING, "ignoring weigher specified without maximumWeight");
  }
}

Wrapper 模式在 Guava 中的应用

Forwarding开头部分类 
@GwtCompatible
public abstract class ForwardingCollection<E> extends ForwardingObject implements Collection<E> {
  protected ForwardingCollection() {
  }
  protected abstract Collection<E> delegate();
  public Iterator<E> iterator() {
    return this.delegate().iterator();
  }
  public int size() {
    return this.delegate().size();
  }
  @CanIgnoreReturnValue
  public boolean removeAll(Collection<?> collection) {
    return this.delegate().removeAll(collection);
  }
  public boolean isEmpty() {
    return this.delegate().isEmpty();
  }
  public boolean contains(Object object) {
    return this.delegate().contains(object);
  }
  @CanIgnoreReturnValue
  public boolean add(E element) {
    return this.delegate().add(element);
  }
  @CanIgnoreReturnValue
  public boolean remove(Object object) {
    return this.delegate().remove(object);
  }
  public boolean containsAll(Collection<?> collection) {
    return this.delegate().containsAll(collection);
  }
  @CanIgnoreReturnValue
  public boolean addAll(Collection<? extends E> collection) {
    return this.delegate().addAll(collection);
  }
  @CanIgnoreReturnValue
  public boolean retainAll(Collection<?> collection) {
    return this.delegate().retainAll(collection);
  }
  public void clear() {
    this.delegate().clear();
  }
  public Object[] toArray() {
    return this.delegate().toArray();
  }
  
  //...省略部分代码...
}

public class AddLoggingCollection<E> extends ForwardingCollection<E> {
  private static final Logger logger = LoggerFactory.getLogger(AddLoggingCollection.class);
  private Collection<E> originalCollection;
  public AddLoggingCollection(Collection<E> originalCollection) {
    this.originalCollection = originalCollection;
  }
  @Override
  protected Collection delegate() {
    return this.originalCollection;
  }
  @Override
  public boolean add(E element) {
    logger.info("Add element: " + element);
    return this.delegate().add(element);
  }
  @Override
  public boolean addAll(Collection<? extends E> collection) {
    logger.info("Size of elements to add: " + collection.size());
    return this.delegate().addAll(collection);
  }
}

public interface Interf {
  void f1();
  void f2();
}
public class OriginalClass implements Interf {
  @Override
  public void f1() { //... }
  @Override
  public void f2() { //... }
}
public class WrapperClass implements Interf {
  private OriginalClass oc;
  public WrapperClass(OriginalClass oc) {
    this.oc = oc;
  }
  @Override
  public void f1() {
    //...附加功能...
    this.oc.f1();
    //...附加功能...
  }
  @Override
  public void f2() {
    this.oc.f2();
  }
}

Immutable 模式在 Guava 中的应用

// 普通不变模式
public class User {
  private String name;
  private int age;
  private Address addr;
  
  public User(String name, int age, Address addr) {
    this.name = name;
    this.age = age;
    this.addr = addr;
  }
  // 只有getter方法，无setter方法...
}
public class Address {
  private String province;
  private String city;
  public Address(String province, String city) {
    this.province = province;
    this.city= city;
  }
  // 有getter方法，也有setter方法...
}
// 深度不变模式
public class User {
  private String name;
  private int age;
  private Address addr;
  
  public User(String name, int age, Address addr) {
    this.name = name;
    this.age = age;
    this.addr = addr;
  }
  // 只有getter方法，无setter方法...
}
public class Address {
  private String province;
  private String city;
  public Address(String province, String city) {
    this.province = province;
    this.city= city;
  }
  // 只有getter方法，无setter方法..
}

public class ImmutableDemo {
  public static void main(String[] args) {
    List<String> originalList = new ArrayList<>();
    originalList.add("a");
    originalList.add("b");
    originalList.add("c");
    List<String> jdkUnmodifiableList = Collections.unmodifiableList(originalList);
    List<String> guavaImmutableList = ImmutableList.copyOf(originalList);
    //jdkUnmodifiableList.add("d"); // 抛出UnsupportedOperationException
    // guavaImmutableList.add("d"); // 抛出UnsupportedOperationException
    originalList.add("d");
    print(originalList); // a b c d
    print(jdkUnmodifiableList); // a b c d
    print(guavaImmutableList); // a b c
  }
  private static void print(List<String> list) {
    for (String s : list) {
      System.out.print(s + " ");
    }
    System.out.println();
  }
}

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