2.spring面试解答

作者: Junma_c631 | 来源:发表于2020-12-02 17:21 被阅读0次

SpringIOC

1.解析配置类Config.class，获取配置类上面@componetScan注解的值package

2.扫描package下的类，并把带有@Compent注解的以及继承自@Compent注解的类，解析成
beanDefintion(bean定义),解析类中定义的@Scope @Lazy 等注解设置为定义的属性,解析完成
放入容器中beanDefintionMap中

3.实例化非懒加载的单例bean
3.1对beanDefintionMap中的bean定义进行合并，放入合并后的bean定义容器中mergedBeanDefinitionMap
3.2.循环遍历合并后的bean定义容器，
根据bean定义中的scope属性查看是否是单例的bean，并查看是否是懒加载，实例化单例非懒加载的bean
实例化之后进行属性填充，
属性填充之后判断bean是否实现了Aware接口，调用Aware接口的实现方法
然后调用bean的初始化方法进行初始化
如果有切面，需要进行动态代理，生成代理bean
把生成的bean放入单例池。bean的实例化过程在spring中是调用bean的不同的后置处理器来完成的。

Spring AOP

切面（创建一个切面类@Aspect,切面类里面定义了很多切点）
切点：@PointCut(com.methd*) 连接点的集合
连接点就是需要切入的某个方法
通知切入的时机+切入的逻辑。@Before("myPointCut")

@Aspect
public class MyAspect {
    //定义一个切点
    @Pointcut("execution(* mjw.spring.aop.dao.*.*(..))")
    public void myPointCut(){
    }
    //定义通知
    @Before("myPointCut()")
    public void beforeAdv(){
        System.out.println("before 通知");
    }
    //也可以吧切点和通知合并配置
    @Before("execution(* mjw.spring.aop.service.*.*(..))")
    public void beforeAdv2(JoinPoint joinPoint){
        System.out.println("before execution");
    }
}

单例作用域的bean中引入原型作用域的Bean的问题

单例作用域的bean中引入原型作用域的Bean的问题
如果一个单例的bean中引用了一个多例的bean，这时候这个多例的bean只会被注入一次，所以达不到多例的效果了，如果想要达到多例的效果可以如下作用：

@Scope("prototype")
@Compent
Class Command{
}


package fiona.apple;

// Spring-API imports
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
@Component
public class CommandManager implements ApplicationContextAware {
    @AutoWared
    private ApplicationContext applicationContext;

    public Object process(Map commandState) {
        // grab a new instance of the appropriate Command
        Command command = createCommand();
        // set the state on the (hopefully brand new) Command instance
        command.setState(commandState);
        return command.execute();
    }

    protected Command createCommand() {
        // 这样每次调用就可以创建一个新的实例,
        //但是这种做法 代码侵入性太高
        return this.applicationContext.getBean("command", Command.class);
    }

    public void setApplicationContext(
            ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
}

@Scope("prototype")
@Component
Class Command{
}
package fiona.apple;

// Spring-API imports
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
@Component
public abstract class CommandManager{
    @LookUp
public abstract Command createCommand();
    public Object process(Map commandState) {
        // grab a new instance of the appropriate Command
        Command command = createCommand();
        // set the state on the (hopefully brand new) Command instance
        command.setState(commandState);
        return command.execute();
    }
}

springMVC

1.  请求进来之后会进入到doDispatch()方法中。
2.  根据request从handlermappings循环获取handler，并构建成一个调用链对象
       HandlerExecutionChain,调用链中包含handler对象以及拦截器。
      注意：springMVC中生命一个controller有三种方式:@Controller注解\实现
      Controller接口\实现HttpRequestHandler接口分别对应三种映射器来获取
      handler对象。这三种方式@Contoller是把对象中的方法解析成一个个handler；
      其余两种其实就是从Spring容器中获取真实的对象。
3.  根据request从匹配出适合的适配器，适配器也有三种分别对应不同的Controller类型,
4.  Chain.applyPreHandle()按顺序调用拦截器
5.  Ha.hand(hand) –通过适配器调用handle对应的方法。其中@Controller类型是通过反射调用，
   期间会通过策略模式，根据不同类型的参数调用不同的参数解析器从request中解析参 
   数值，然后通过反射调用controller的方法;根据方法的返回值以及方法上有没有加@ResponseBody注解，
   来判断是走视图解析器还是走消息转换器。
6.  Chain.applyPostHandle()调用拦截器
7.  调用视图解析器渲染参数以及页面跳转。

手写springMVC

1.tomcat启动类

package com.luban.springmvc;
import com.luban.springmvc.servlet.DispatcherServlet;
import org.apache.catalina.Context;
import org.apache.catalina.core.StandardContext;
import org.apache.catalina.startup.Tomcat;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;

@ComponentScan("com.luban")
public class Start {

    public static void main(String[] args) throws Exception {
        Tomcat tomcat = new Tomcat();
        tomcat.setPort(8080);
        tomcat.addWebapp("/", "D:\\workspace\\springmvc\\src\\main\\webapp");
        tomcat.start();
        tomcat.getServer().await();
    }
}

2.基于servlet3.0规范利用SPI机制web容器启动完毕之后加载DispatcherServlet

image.png

#com.luban.springmvc.init.Myinit
package com.luban.springmvc.init;

import com.luban.springmvc.Start;
import com.luban.springmvc.servlet.DispatcherServlet;
import org.apache.jasper.servlet.JspServlet;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletRegistration;
import java.util.Set;

//SPI
public class Myinit implements ServletContainerInitializer{

    @Override
    public void onStartup(Set<Class<?>> c,ServletContext servletContext) {
        AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext(Start.class);
        DispatcherServlet servlet = new DispatcherServlet(ac);
        ServletRegistration.Dynamic dy = servletContext.addServlet("app",servlet);
        dy.setLoadOnStartup(1);
        dy.addMapping("*.do");
      /*  JspServlet jspServlet = new JspServlet();
        ServletRegistration.Dynamic dy1 = servletContext.addServlet("app1",jspServlet);
        dy1.setLoadOnStartup(2);
        dy1.addMapping("*.jsp");*/
    }
}

3.DispatcherServlet

package com.luban.springmvc.servlet;

import com.luban.springmvc.init.handlerAdapter.HandlerAdapter;
import com.luban.springmvc.init.handlerMapping.HandlerMapping;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Collection;
import java.util.Map;

public class DispatcherServlet extends HttpServlet {
    static Collection<HandlerAdapter> handlerAdapters ;
    static Collection<HandlerMapping> handlerMappings ;

    public DispatcherServlet() {
    }

    public DispatcherServlet(AnnotationConfigApplicationContext ac) {
        //组件初始化
        Map<String, HandlerMapping> handlerMappingMaps = ac.getBeansOfType(HandlerMapping.class);
        handlerMappings = handlerMappingMaps.values();

        Map<String, HandlerAdapter> handlerAdapterMaps = ac.getBeansOfType(HandlerAdapter.class);
        handlerAdapters = handlerAdapterMaps.values();
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException {
        Object handlerMapping = getHandlerMapping(req);
        if(handlerMapping == null){
            System.out.println("未匹配到handlerMapping");
            return;
        }
        HandlerAdapter handlerAdapter = getHandlerAdapter(handlerMapping);
        if(handlerAdapter == null){
            System.out.println("未匹配到handlerAdapter");
            return;
        }
        Object result = handlerAdapter.handle(req,resp,handlerMapping);

        PrintWriter writer = resp.getWriter();
        writer.println(result);
        writer.flush();
        writer.close();
    }

    protected Object getHandlerMapping(HttpServletRequest request) {
        if (this.handlerMappings != null) {
            for (HandlerMapping mapping : this.handlerMappings) {
                Object handler = mapping.getHandlerMapping(request.getRequestURI());
                if (handler != null) {
                    return handler;
                }
            }
        }
        return null;
    }

    protected HandlerAdapter getHandlerAdapter(Object handlerMapping) {
        if (this.handlerAdapters != null) {
            for (HandlerAdapter adapter : this.handlerAdapters) {
                boolean flag = adapter.supports(handlerMapping);
                if (flag) {
                    return adapter;
                }
            }
        }
        return null;
    }

}

4.HandlerMapping

package com.luban.springmvc.init.handlerMapping;

public interface HandlerMapping {
    Object getHandlerMapping(String requestURI);
}

package com.luban.springmvc.init.handlerMapping;

import com.luban.springmvc.controller.Controller;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.stereotype.Component;

import java.util.HashMap;
import java.util.Map;

@Component
public class BeanNameHandlerMapping  implements HandlerMapping,InstantiationAwareBeanPostProcessor {

    public static Map<String, Controller> map = new HashMap<>();

    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        if(beanName.startsWith("/")){
            map.put(beanName,(Controller)bean);
        }
        return true;
    }

    @Override
    public Object getHandlerMapping(String requestURI) {
        return map.get(requestURI);
    }
}

package com.luban.springmvc.init.handlerMapping;

import com.luban.springmvc.annotation.RequestMapping;
import com.luban.springmvc.servlet.RequestMappingInfo;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.stereotype.Component;

import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

@Component
public class AnnotationHadlerMapping  implements HandlerMapping,InstantiationAwareBeanPostProcessor {

    public static Map<String,RequestMappingInfo> map = new HashMap<>();

    @Override
    //bean里面会有多个处理器
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        Method[] methods = bean.getClass().getDeclaredMethods();
        for(Method method : methods){
            RequestMappingInfo requestMappingInfo = createRequestMappingInfo(method,bean);
            map.put(requestMappingInfo.getUri(),requestMappingInfo);
        }
        return true;
    }

    private RequestMappingInfo createRequestMappingInfo(Method method,Object bean) {
        RequestMappingInfo requestMappingInfo = new RequestMappingInfo();
        if(method.isAnnotationPresent(RequestMapping.class)){
            requestMappingInfo.setMethod(method);
            requestMappingInfo.setUri(method.getDeclaredAnnotation(RequestMapping.class).value());
            requestMappingInfo.setObj(bean);
        }
        return requestMappingInfo;
    }

    @Override
    public Object getHandlerMapping(String requestURI) {
        return map.get(requestURI);
    }
}

6.HandlerAdapter

package com.luban.springmvc.init.handlerAdapter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface HandlerAdapter {
    //该方法判断handler是否是跟该适配器对应的Handler
    public boolean supports(Object handler);
    //执行handler的业务方法
    public Object handle(HttpServletRequest request, HttpServletResponse response, Object handler);
}

package com.luban.springmvc.init.handlerAdapter;
import com.alibaba.fastjson.JSON;
import com.luban.springmvc.annotation.RequestParam;
import com.luban.springmvc.annotation.ResponseBody;
import com.luban.springmvc.servlet.RequestMappingInfo;
import org.springframework.stereotype.Component;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.util.Map;
@Component
public class AnnotationHandlerAdapter implements HandlerAdapter{
    @Override
    public boolean supports(Object handler) {
        //判断是否是RequestMapping子类
        return (handler instanceof RequestMappingInfo);
    }
    @Override
    //参数绑定
    public Object handle(HttpServletRequest request, HttpServletResponse response, Object handler){
        RequestMappingInfo requestMappingInfo = (RequestMappingInfo)handler;
        Map<String, String[]> paramMap = request.getParameterMap();//请求携带的参数
        Method method = requestMappingInfo.getMethod();//方法定义的参数
        Parameter[] parameters = method.getParameters();

        Object[] params = new Object[method.getParameterTypes().length];
        for(int i=0; i<parameters.length; i++){
            for(Map.Entry<String, String[]> entry : paramMap.entrySet()){
                if(parameters[i].getAnnotation(RequestParam.class) != null && entry.getKey()!= null &&
                        entry.getKey().equals(parameters[i].getAnnotation(RequestParam.class).value())){
                    params[i] = entry.getValue()[0];
                //jdk1.8实现反射获取方法名   1.8之前使用asm实现
                }else if(entry.getKey().equals(parameters[i].getName())){
                    params[i] = entry.getValue()[0];
                }
            }

            //传入request和response
            if(ServletRequest.class.isAssignableFrom(parameters[i].getType())){
                params[i] = request;
            }else if(ServletResponse.class.isAssignableFrom(parameters[i].getType())){
                params[i] = response;
            }
        }

        try {
            Object result = method.invoke(requestMappingInfo.getObj(),params);
            if (result instanceof String) {
                if ("forward".equals(((String) result).split(":")[0])) {
                    request.getRequestDispatcher(((String) result).split(":")[1]).forward(request, response);
                } else {
                    response.sendRedirect(((String) result).split(":")[1]);
                }
            }else{
                if(method.isAnnotationPresent(ResponseBody.class)){
                    return JSON.toJSONString(result);
                }
            }

            return result;
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

package com.luban.springmvc.init.handlerAdapter;

import com.luban.springmvc.controller.Controller;
import org.springframework.stereotype.Component;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@Component
public class BeanNameHandlerAdapter implements HandlerAdapter{
    @Override
//    //判断hanlde是否适配当前适配器
    public boolean supports(Object handler) {
        //判断是否是RequestMapping子类
        return (handler instanceof Controller);
    }

    @Override
    public Object handle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        return ((Controller)handler).handler(request, response);
    }
}

7.RequestMappingInfo

package com.luban.springmvc.servlet;

import java.lang.reflect.Method;

public class RequestMappingInfo {

    private Method method;

    private String uri;

    private Object obj;

    public Object getObj() {
        return obj;
    }

    public void setObj(Object obj) {
        this.obj = obj;
    }

    public Method getMethod() {
        return method;
    }

    public void setMethod(Method method) {
        this.method = method;
    }

    public String getUri() {
        return uri;
    }

    public void setUri(String uri) {
        this.uri = uri;
    }
}

7.Controller接口

package com.luban.springmvc.controller;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface Controller {
    Object handler(HttpServletRequest request, HttpServletResponse response);
}

8.springMVC的controller类

public class HelloController {
    @Autowired
    HelloService service;
    @RequestMapping("/test.do")
    public String test(HttpServletRequest request, HttpServletResponse response,
                     @RequestParam("param") String param){
        System.out.println("param:"+param);
        service.test(param);
        request.setAttribute("param",param);
        return "forward:/test.jsp";
    }

    @RequestMapping("/test1.do")
    @ResponseBody
    public Map test1(String param){
        Map map = new HashMap();
        map.put("param",param);
        return map;
    }
    @RequestMapping("/test2.do")
    @ResponseBody
    public User test2(String param){
        User user = new User();
        user.setName(param);
        user.setAge(param);
        return user;
    }
}

@Component("/testController")//通过id定义url
public class TestController implements Controller{
    @Override
    public Object handler(HttpServletRequest request, HttpServletResponse response) {
        System.out.println("TestController");
        return null;
    }
}

2.spring面试解答

SpringIOC

Spring AOP

单例作用域的bean中引入原型作用域的Bean的问题

springMVC

手写springMVC

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