设计模式课程 设计模式精讲 19-3 策略模式源码解析

1　　　　源码解析

1.1　　　　源码解析1（jdk中的应用1）

1.2　　　　源码解析2（jdk中的应用2）

1.3　　　　源码解析3（Spring中的应用1）

1.4　　　　源码解析4（Spring中的应用2）

1　　　　源码解析

1.1　　　　源码解析1（jdk中的应用1）

java.util.Comparator（策略类）作为比较器的应用

package java.util;


public interface Comparator<T> {
  
    int compare(T o1, T o2);

    boolean equals(Object obj);
}

java.util.ArrayList（策略类应用）

package java.util;

import java.lang.reflect.*;

public class Arrays {

    public static <T> void sort(T[] a, Comparator<? super T> c) {
        if (LegacyMergeSort.userRequested)
            legacyMergeSort(a, c);
        else
            TimSort.sort(a, c);
    }

}

1.2　　　　源码解析2（jdk中的应用2）

java.util.Comparator（策略类）作为比较器的应用

package java.util;


public interface Comparator<T> {
  
    int compare(T o1, T o2);

    boolean equals(Object obj);
}

java.util.TreeMap（策略类应用）

public class TreeMap<K,V>
    extends AbstractMap<K,V>
    implements NavigableMap<K,V>, Cloneable, java.io.Serializable
{
    /**
     * The comparator used to maintain order in this tree map, or
     * null if it uses the natural ordering of its keys.
     *
     * @serial
     */
    private final Comparator<? super K> comparator;

　　//此处涉及到泛型的应用，关于泛型==》详细可以查看文章 ==》java后台==》数据类型==》泛型使用部分
   final int compare(Object k1, Object k2) {
        return comparator==null ? ((Comparable<? super K>)k1).compareTo((K)k2)
            : comparator.compare((K)k1, (K)k2);
    }
｝

1.3　　　　源码解析3（Spring中的应用1）诸多方法被策略行为类调用

org.springframework.core.io.Resource（策略抽象）

package org.springframework.core.io;

import java.io.File;
import java.io.IOException;
import java.net.URI;
import java.net.URL;

public interface Resource extends InputStreamSource {
    boolean exists();

    boolean isReadable();

    boolean isOpen();

    URL getURL() throws IOException;

    URI getURI() throws IOException;

    File getFile() throws IOException;

    long contentLength() throws IOException;

    long lastModified() throws IOException;

    Resource createRelative(String var1) throws IOException;

    String getFilename();

    String getDescription();
}

策略行为类：FileSystemResource，ClassPathResource，InputStreamResource，PathResource等等

1.4　　　　源码解析4（Spring中的应用2之bean的初始化应用）（特殊之处是策略行为之间继承，共同实现策略类）

InstantiationStrategy（初始化策略接口）

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.springframework.beans.factory.support;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;

public interface InstantiationStrategy {
    Object instantiate(RootBeanDefinition var1, String var2, BeanFactory var3) throws BeansException;

    Object instantiate(RootBeanDefinition var1, String var2, BeanFactory var3, Constructor<?> var4, Object[] var5) throws BeansException;

    Object instantiate(RootBeanDefinition var1, String var2, BeanFactory var3, Object var4, Method var5, Object[] var6) throws BeansException;
}

SimpleInstantiationStrategy （策略父类）

package org.springframework.beans.factory.support;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;
import org.springframework.beans.BeanInstantiationException;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

public class SimpleInstantiationStrategy implements InstantiationStrategy {
    private static final ThreadLocal<Method> currentlyInvokedFactoryMethod = new ThreadLocal();

   public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) {
        ...
    }

    protected Object instantiateWithMethodInjection(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) {
        throw new UnsupportedOperationException("Method Injection not supported in SimpleInstantiationStrategy");
    }

    public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner, final Constructor<?> ctor, Object[] args) {
        ...
    }

    protected Object instantiateWithMethodInjection(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner, Constructor<?> ctor, Object[] args) {
        throw new UnsupportedOperationException("Method Injection not supported in SimpleInstantiationStrategy");
    }

    public Object instantiate(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner, Object factoryBean, final Method factoryMethod, Object[] args) {
        ...
    }
}

CglibSubclassingInstantiationStrategy （策略子类）

package org.springframework.beans.factory.support;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.BeanInstantiationException;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.cglib.core.SpringNamingPolicy;
import org.springframework.cglib.proxy.Callback;
import org.springframework.cglib.proxy.CallbackFilter;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.Factory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
import org.springframework.cglib.proxy.NoOp;

public class CglibSubclassingInstantiationStrategy extends SimpleInstantiationStrategy {
    private static final int PASSTHROUGH = 0;
    private static final int LOOKUP_OVERRIDE = 1;
    private static final int METHOD_REPLACER = 2;

    public CglibSubclassingInstantiationStrategy() {
    }

    protected Object instantiateWithMethodInjection(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) {
        return this.instantiateWithMethodInjection(beanDefinition, beanName, owner, (Constructor)null, (Object[])null);
    }

    protected Object instantiateWithMethodInjection(RootBeanDefinition beanDefinition, String beanName, BeanFactory owner, Constructor<?> ctor, Object[] args) {
        return (new CglibSubclassingInstantiationStrategy.CglibSubclassCreator(beanDefinition, owner)).instantiate(ctor, args);
    }
...
    
}