java初探之代理模式

代理模式

代理模式一般有三种角色：

没有使用代理模式的话可能就会直接去操作真实的对象

加入代理模式就是加入了 隔离 把我们的真实对象与调用者隔离了一下(代理对象)

代理对象的好处？

使用者(client)跟真实的对象是没有直接的交集的。不会直接操作到真实对象

实例

//1.代理角色对象 定义了服务的接口
public interface Massage{
    void message();
}

//2.真实的实现类：提供马杀鸡服务的路西
public class Lucy implements Massage{
    
    @Override
    public void message(){
        System.out.println("手法一流");
    }
}


public class Alvin implements Massage{
    
    @Override
    public void massage(){
        System.out.println("精通各种手法")
    }
}

//3.代理对象 马杀鸡经纪人
public class Agent implements Massage{
    private final Massage massage;
    
    public Agent(Massage massage){
        this.massage = massage;
    }
    
    //前置处理
    public void before(){
        System.out.println("前置开始");
    }
    
    //后置处理
    public void after(){
        System.out.println("后置处理");
    }
    
    @Override
    public void massage(){
        before();
        massage.massage();
        after();
    }
}

public class MyClass{
    public static void main(String[] args) throws Exception{
        //静态代理
        Massage massage = new Lucy();
        Agent agent = new Agent(massage);
        
        agent.massage();//没有直接跟lucy交互
        
}

每个代理类只能为一个接口来服务

如果有多个功能就要写多个代理类如：

public class WashAgent implements Wash{
    @Override
    public void wash(){
        
    }
}

想办法通过一个代理类实现全部的代理功能！->动态代理

public class MyClass{
    public static void main(String[] args) throws Exception{
          
         //动态代理 完成足浴与按摩
        
        Alvin alvin = new Alvin();//真实的要操作的对象
        
        //Proxy创建 动态代理对象
        Object o = Proxy.newProxyInstance(MyClass.class.getClassLoader(),new Class[]{Message.class,Wash.class},new InvocationHandler(){
            @OVerride
            public Object invoke(Object o,Method method,Object[] objects)throws Throwable{
                //System.out.println(o.toString()); 死循环 o就是Object o 调用o.任何方法都会进入invoke()中 就会一直调然后死循环
                //invoke(在那个对象上执行的方法，方法参数)
                return method.invoke(alvin,objects);
            }
        });
        
        Massage massage = (Massage) o;
        massage.massage();
        
        Wash wash = (Wash) o;
        wash.wash();
    }
}


public class Alvin implements Massage,Wash{
    
    @Override
    public void massage(){
        System.out.println("massage...");
    }
    
    @Override
    public void wash(){
        System.out.println("washing...");
    }
}

源码解析

Proxy.class:
 //生成 class数据 动态代理为我们创建的对象 
byte[] var22 = ProxyGenerator.generateProxyClass(var23,var2,var17);



test:
private static void proxy() throws Exception{
    String name = Massage.class.getName()+"$Proxy0";
    //生成代理指定接口的class数据
    byte[] bytes = ProxyGenerator.generateProxyClass(name,new Class[]{Massage.class});
    FileOutputStream fos = new FileOutputStream("lib/"+name+".class");
    fos.wirte(bytes);
    fos.close();
}

com.enjoy.lib.Massage$Proxy0.class

public final class Massage$Proxy0 extends Proxy implements Massage{
    
    public Massage$Proxy0(InvocationHandler var1)throws{
        //这里的invovationHandler就是new ProxyInstance传入的
        super(var1);
    }
    
    public final void massage() throws{
        try{
           //super.h===var1;
            //给接口赋值 这样newProxyInstance就会被回调出去
           super.h.invoke(this,m3,(Object][])null); 
        }catch(Throwable var3){
            throw new UndeclaredThrowableException(var3);
        }
    }
    
    public final String toString() throws{
        try{
            return (String)super.h.invoke(this,m2,(Object[])null);
        }catch(Throwable var3){
            throw new UndeclaredThrowableException(var3);
        }
    }
    
}    

Retrofit实操

public interface WetherApi{
    
    @POST("/v3/weather/weatherInfo")
    @FormUrlEncoded
    Call<ResponseBody> getWeather(@Field("city") String city,@Field("key") String key);
    
    @GET("/v3/weather/weatherInfo")
    Call<ResponseBody> getWeather(@Query("city") String city,@Query("key") String key);
}

Retrofit retrofit = new Retrofit.Builder().baseUrl("https://restapi.amap.com").build();

//create()就是内部完成了动态代理 
WeatherApi weatherApi = retrofit.create(WetherApi.class);

public class EnjoyRetrofit{
    //第一次调用解析一次 第二次调用又去解析一次吗
    final Map<Method,ServiceMethod> serviceMethodCache = new ConcurrentHashMap<>();
    final Call.Factory callFactory;
    final HttpUrl baseUrl;
    
    EnjoyRetrofit(Call.Factory callFactory,HttpUrl baseUrl){
        this.callFactory = callFactory;
        this.baseUrl = baseUrl;
    }
    
    public <T> T create(final Class<T> service){
        return (T) Proxy.newInstance(service.getClassLoader(),new Class[]{service},new InvocationHandler(){
           @Override
            public Object invoke(Object proxy,Method method,Object[] args) throws Throwable{
                //实现对应的postWeather/getWeather
                //解析method上所有的注解信息
                loadServiceMethod(method);
                return serviceMethod.invoke(args);//返回Call
                
            }
        });
    }
    
    
    //解析方法上的注解
    private ServiceMethod loadServiceMethod(Method method){
        //先不上锁 避免synchronized的性能损耗
        ServiceMethod result = serviceMethodCache.get(method);
        if(result!=null) return result;
        //多线程下避免重复解析
        synchronized(serviceCache){
            //线程A和B进入时 A先进 result=null 给result赋值后B进入 如果不判断是否为空 会再次解析一次 
            result = serviceCache.get(method);
            if(result==null){
                result = new ServiceMethod.Builder(this,method).build();
                serviceMethodCache.put(method,result);
            }
        }
        return result;
    }
    
    
    //构建者模式 不需要关心成员的细节 只需要关心你想要设置的内容  很好的屏蔽掉细节
    public static final class Builder{
        private HttpUrl baseUrl;
        private okhttp3.Call.Factory callFactory;
        
        public Builder callFactory(okhttp3.Call.Factory factory){
            this.callFactory = factory;
            return this;
        }
        
        public Builder baseUrl(String baseUrl){
            this.baseUrl = HttpUrl.get(baseUrl);
            return this;
        }
        
        public EnjoyRetrofit build(){
            if(baseUrl==null){
                throw new IllegalStateException("Base URL,required");
            }
            okhttp3.Call.Factory callFactory = this.callFactory;
            if(callFactory==null){
                callFactory = new OkHttpClient();
            }
            return new EnjoyRetrofit(callFactory,baseUrl);
        }
    }
}
//可以设置也可以不设置 build会进行校验  
EnjoyRetrofit.Builder().baseUrl("https").callFactory(new OkHttpClient.Builder().callTimeout(1)).build();

//记录请求类型 请求参数 完整地址
public class ServiceMethod{
    
    String baseUrl;
    private final okhttp3.Call.Factory callFactory;
    String httpMethod;
    String relativeUrl;
    Boolean hasBody;
    private FormBody.Builder formBuild;
    //每个参数的key
    ParameterHandler[] parameterHandler;
    HttpUrl.Builder urlBuilder;//完整的url
    
    public ServiceMethod(Builder builder){
        baseUrl = builder.enjoyRetrofit.baseUrl;
        callFactory = builder.enjoyRetrofit.callFactory;
        
        httpMethod = builder.httpMethod;
        relativeUrl = builder.relativeUrl;
        hasBody = builder.hasBody;
        parameterHandler = builder.parameterHandler;
        //如果有请求体 创建 一个okhttp的请求体对象 
        if(hasBody){
            formBuild = new FormBody.Builder();
        }
    }
    
    
    public Object invoke(Object[] args){
        //处理请求的地址与参数 重点
        for(int i=0;i<parameterHandler.length;i++){
            ParameterHandler handlers = parameterHandler[i]; //handler记录了key
            //handler内本来就记录了key 现在给到了对应的value
            handlers.apply(this,args[i].toString());//this->ServiceMethod记录了请求地址 args[i]记录了参数的value
        }
        //获取最终请求地址
        HttpUrl url;
        if(urlBuilder ==null){//说明不是get请求
            urlBuilder = baseUrl.newBuilder(relativeUrl); 
        }
        url = urlBuilder.build();
        //请求体
        FormBody formBody = null;
        if(formBuild!=null){
           formBody =  formBuild.build();
        }
        
        //使用okhttp发送请求 get请求时formBody==null没关系可以传入
        Request request = new Request.Builder().url(url).method(httpMethod,formBody).build();
        
        return callFactory.newCall(request);
    }
     
    
    //get请求 把k-v 拼到url里面
    public void addQueryParameter(String key,String value){
        if(urlBuilder ==null){
            urlBuilder = baseUrl.newBuilder(relativeUrl);
        }
        urlBuilder.addQuery(key,value);
    }
    
    //吧k-v放到请求体中
    public void addFieldParameter(String key,String value){
        formBuild.add(key,value);
    }
     
    public static class Builder{
        private final EnjoyRetrofit enjoyRetrofit;
        private final Annotation[] methodA nnotations;
        private final Annotation[][] parameterAnnotations;
        private String httpMethod;
        private String relativeUrl;
        private Boolean hasBody;
        private ParameterHandler[] parameterHandler;
        
        public Builder(EnjoyRetrofit enjoyRetrofit,Method method){
            this.enjoyRetrofit = enjoyRetrofit;
            //获取方法上的所有注解
            methodAnnotations = method.getAnnotations();
            //获得方法参数的所有的注解(一个参数可以有多个注解，一个方法又会有多个参数)
            paramterAnnotations = method.getParameterAnnotations();
            
        }
        
        public ServiceMethod build(){
            //1.解析方法上的注解 只处理POST和GET
            for(Annotation methodAnnotation:methodAnnotations){
                if(methodAnnotation instance of POST){//post请求
                    //记录当前请求方式
                    this.httpMethod = "POST";
                    //记录当前url的path
                    this.relativeUrl = ((POST) methodAnnotation).getValue();
                    //是否有请求体
                    this.hasBody = true;
                }else if(methodAnnotation instance of GET){
                    this.httpMethod = "GET";
                    this.relativeUrl = ((GET) methodAnnotation).getValue();
                    this.hasBody = false;
                }
            }
            //2.解析方法参数的注解
           
            int length = paramterAnnotations.length;//有多少个参数
            parameterHandler = new ParameterHandler[length];
            for(int i=0;i< length;i++){
                //一个参数上面所有的注解
                Annotation[] annotations = parameterAnnotations[i];
                //处理参数上的每一个注解
                for(Annotation annotation:annotations){
                    if(annotation instance of Field){
                        //得到注解上的value 请求参数的key
                        String value = ((Field) annotation).getValue();
                        //又在一个新的类中记录了请求参数的key
                        parameterHandler[i] = new ParameterHandler.FieldParameterHandler(value);
                    }else if(annotation instance of Query){
                        String value = ((Query) annotation).getValue();
                        parameterHandler[i] = new ParameterHandler.QueryParameterHandler(value);
                    }
                }
            }
           
            
            return new ServiceMethod(this);
        }
    } 
}

//
public abstract class ParameterHandler{
    
    abstract void apply(ServiceMethod serviceMethod,String value);
    
    //只处理get请求 没有请求头
    static class QueryParameterHandler extends ParameterHandler{
        String key;
        public QueryParameterHandler(String key){
            this.key = key;
        }
        
        @Override
        void apply(ServiceMethod serviceMethod,String value){
            serviceMethod.addQueryParameter(key,value);//回调到serviceMethod中
        }
    }
    
    //只处理post请求 带请求头
    static class FiledParameterHander extends ParameterHandler{
        String key;
        
        public FiledParameterHandler(String key){
            this.key = key;
        }
        
        @Override
        void apply(ServiceMethod serviceMethod,String value){
            serviceMethod.addFieldParameter(key,value);//回调到serviceMethod中
        }
    }
}

/回调到serviceMethod中
}
}

//只处理post请求 带请求头
static class FiledParameterHander extends ParameterHandler{
    String key;
    
    public FiledParameterHandler(String key){
        this.key = key;
    }
    
    @Override
    void apply(ServiceMethod serviceMethod,String value){
        serviceMethod.addFieldParameter(key,value);//回调到serviceMethod中
    }
}

}