java reflect

java 反射得到方法
为了直接得到org.apache.http.impl.client.RequestWrapper{public boolean containsHeader(java.lang.String);}
public RequestWrapper(HttpRequest request) throws ProtocolException 构造函数带参数 （目标）
要用getDeclaredConstructor

newinstance中必须传入实例 如第8行
而httprequest是个interface 没有实例，必须得到其实例类BasicHttpEntityEnclosingRequest的class （见http://hc.apache.org/httpcomponents-core-ga/httpcore/apidocs/org/apache/http/HttpRequest.html?is-external=true）

public static void main( String[] args ) throws IOException, ClassNotFoundException
{
try {
Class baseRequestClazz = Class.forName("org.apache.http.message.BasicHttpEntityEnclosingRequest");//得到class
Constructor baseRequestCon = baseRequestClazz.getDeclaredConstructor(String.class, String.class);//得到构造函数
baseRequestCon.setAccessible(true);

Object[] baseRequestParams = {new String("A"), new String("B")};
Object baseRequestInstance = baseRequestCon.newInstance(baseRequestParams);//根据构造函数得到一个实例

Class httpRequestClazz = Class.forName("org.apache.http.HttpRequest");//得到httprequst的class，为了得到构造函数的参数
Class httpWrapperClazz = Class.forName("org.apache.http.impl.client.RequestWrapper");//构造函数的class
Constructor httpWrapperCon = httpWrapperClazz.getDeclaredConstructor(httpRequestClazz);
Object httpWrapperInstance = httpWrapperCon.newInstance(baseRequestInstance);//根据构造函数得到一个实例

Method method = httpWrapperClazz.getMethod("containsHeader", String.class);//申明class的中的方法
Object obj = method.invoke(httpWrapperInstance,"day");//invoke 根据实例和方法得到方法的返回值（必为object）
//http://javaweb.cc/JavaAPI1.6/
System.out.println(obj.toString());
System.out.println(obj.getClass());
if ((Boolean)obj) //其实就是boolean直接强转
System.out.println("yes");
else
System.out.println("no");
}catch(Exception e) {
e.printStackTrace();
}

}

下面再来一个复杂的例子

各种查api才能知道要哪些实例

Class : org.apache.http.impl.client.AbstractAuthenticationHandler

为了得到这个方法Method::public abstract boolean isAuthenticationRequested(org.apache.http.HttpResponse, org.apache.http.protocol.HttpContext);
interface HttpResponse --- BasicHttpResponse(ProtocolVersion ver, int code, String reason)
--- ProtocolVersion(String protocol, int major, int minor)
org.apache.http.protocol.HttpContext BasicHttpContext()

            Class ProtocolVersionClass = Class.forName("org.apache.http.ProtocolVersion");
            Constructor ProtocolVersionCon = ProtocolVersionClass.getDeclaredConstructor(String.class,int.class,int.class);
            ProtocolVersionCon.setAccessible(true);
            Object[] ProtocolVersionParams = {new String("A"), new Integer(6), new Integer(6)};
            Object ProtocolVersionEx = ProtocolVersionCon.newInstance(ProtocolVersionParams);

            Class BasicHttpResponseClass = Class.forName("org.apache.http.message.BasicHttpResponse");
            Constructor BasicHttpResponseCon = BasicHttpResponseClass.getDeclaredConstructor(ProtocolVersionClass,int.class,String.class);
            Object BasicHttpResponseEx = BasicHttpResponseCon.newInstance(ProtocolVersionEx,new Integer(6),new String("A"));
            Class AbstractAuthenticationHandlerClass = Class.forName("org.apache.http.client.AuthenticationHandler");
            //Object HttpResponsEx = AbstractAuthenticationHandlerCon.newInstance(BasicHttpResponseEx);

            Class HttpResponseClass = Class.forName("org.apache.http.HttpResponse");

            Class HttpContextClass = Class.forName("org.apache.http.protocol.HttpContext");
            Class BasicHttpContextClass = Class.forName("org.apache.http.protocol.BasicHttpContext");
            Object BasicHttpContextEx = BasicHttpContextClass.newInstance();
            //Object HttpContextEx = HttpContextClass.newInstance();

            Class AuthenticationHandlerClass = Class.forName("org.apache.http.impl.client.DefaultProxyAuthenticationHandler");
            Object AuthenticationHandlerEx = AuthenticationHandlerClass.newInstance();
            Method method = AuthenticationHandlerClass.getMethod("isAuthenticationRequested",HttpResponseClass,HttpContextClass);
            Object obj = method.invoke(AuthenticationHandlerEx,BasicHttpResponseEx,BasicHttpContextEx);
            System.out.println(obj.toString());