springmvc之定制简易注解框架

柔光的暖阳◎ 2022-04-23 02:38 150阅读 0赞

### 一.前言 ###

定制化手写注解实现SpringMVC底层原理。虽然代码简单，但是五脏俱全，实现了springmvc原理的整个过程。先了解下springmvc的原理流程图：  
![在这里插入图片描述][SouthEast]

### 二.实现流程 ###

###### 项目工程目录 ######

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA1MjAxNDY_size_16_color_FFFFFF_t_70]

**poml文件添加**

<dependency>
                <groupId>javax.servlet</groupId>
                <artifactId>javax.servlet-api</artifactId>
                <version>3.0.1</version>
                <scope>provided</scope>
            </dependency>

**增加web.xml**

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
             xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
             version="3.0">
      <servlet>
        <servlet-name>DispatcherServlet</servlet-name>
        <servlet-class>com.sxkj.servlet.DispatcherServlet</servlet-class>
        <init-param>
          <param-name>contextConfigLocation</param-name>
          <param-value> config/application.properties</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
      </servlet>
      <servlet-mapping>
        <servlet-name>DispatcherServlet</servlet-name>
        <url-pattern>/*</url-pattern> </servlet-mapping> </web-app>

###### 1.定义注解 ######

**1.CustomController**

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface CustomController { 
        String value() default "";
    }

**2.CustomService**

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface CustomService { 
        String value() default "";
    }

**3.CustomRequstMapping**

@Target({ ElementType.TYPE,ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface CustomRequstMapping { 
        //表示访问该方法的url
        String value() default "";
    }

**4.CustomAutowired**

@Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface CustomAutowired { 
        String value() default "";
    }

**5.CustomRequstParam**

@Target(ElementType.PARAMETER)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface CustomRequstParam { 
        //表示参数的别名，必填
        String value() ;
    }

##### 2.添加controller层方法UserController #####

@CustomController
    @CustomRequstMapping("/test")
    public class UserController { 
        @CustomAutowired(value = "UserServiceImpl")
        UserServiceInter userServiceInter;
    
        @CustomRequstMapping("/getName")
        public void getUserName(HttpServletResponse response,@CustomRequstParam("id") String id) throws IOException { 
            String userName = userServiceInter.getUserName(id);
            PrintWriter writer = response.getWriter();
            writer.write(userName);
        }
    }

##### 3.添加service层方法 #####

UserServiceInter

public interface UserServiceInter { 
        String getUserName(String id);
    }

UserServiceImpl

@CustomService(value = "UserServiceImpl")
    public class UserServiceImpl implements UserServiceInter { 
        @Override
        public String getUserName(String id) { 
            System.out.println("用户Id:"+id);
            return "hello,id:"+id;
        }
    }

##### 4.添加servlet,DispatcherServlet(主要实现) #####

public class DispatcherServlet extends HttpServlet { 
        //存放扫描包下的所有文件集合
        private List<String> mClassNames=new ArrayList<String>();
        //存放实例化对象的集合容器 Customcontroller,Customservice注解的对象
        private Map<String,Object> mBeans=new HashMap<String, Object>();
        //存放url映射的路径信息
        private HashMap<String,Object> mHandleUrlMapping=new HashMap<String, Object>();
    
        @Override
        public void init() throws ServletException { 
            super.init();
            System.out.println("初始化");
            initScanFile("com.sxkj");//扫描所有的包下目录的所有文件
            initInstance();//初始化实例化对象
            initAutowired();//实例化autowired注解对象到该类的controller字段对象
            initHandleUrlMapping();//处理url映射关系
        }
    
        /** * @Description 处理url映射关系 **/
        private void initHandleUrlMapping() { 
            for (Map.Entry<String,Object> entry:mBeans.entrySet()) { 
                //遍历集合容器中的对象
                Object instance = entry.getValue();
                //根据实例化对象拿到类的对象
                Class<?> clazz = instance.getClass();
                //判断是否为控制类
                if (clazz.isAnnotationPresent(CustomController.class)) { 
                    //拿到customRequstMapping注解对象
                    CustomRequstMapping customRequstMapping=clazz.getAnnotation(CustomRequstMapping.class);
                    //拿到controller上改注解的值 如:/test
                    String classPath = customRequstMapping.value();
                    //拿到该类的所有方法
                    Method[] methods = clazz.getMethods();
                    for (Method method:methods){ 
                        //判断该方法是否有customRequstMapping注解
                        if(method.isAnnotationPresent(CustomRequstMapping.class)){ 
                            //拿到customRequstMapping注解对象
                            CustomRequstMapping requstMapping=method.getAnnotation(CustomRequstMapping.class);
                            //拿到该值 如:/getName
                            String methodPath = requstMapping.value();
                            //将路径 /test/getName 放入map容器中
                            mHandleUrlMapping.put(classPath+methodPath,method);
                        }else { 
                            continue;
                        }
                    }
                }else { 
                    continue;
                }
            }
        }
    
        /** * @Description 初始实例化autowired注解的对象 **/
        private void initAutowired() { 
            for (Map.Entry<String,Object> entry:mBeans.entrySet()){ 
                //遍历集合容器中的对象
                Object instance = entry.getValue();
                //根据实例化对象拿到类的对象
                Class<?> clazz=instance.getClass();
                if(clazz.isAnnotationPresent(CustomController.class)){ 
                    //获取该类的成员变量
                    Field[] fields = clazz.getDeclaredFields();
                    //遍历成员变量
                    for (Field field:fields){ 
                        //判断该变量是否有customAutored注解
                        if(field.isAnnotationPresent(CustomAutowired.class)){ 
                            CustomAutowired customAutowired=field.getAnnotation(CustomAutowired.class);
                            //获取该注解的value值,该值为mBean的key值
                            String key = customAutowired.value();
                            //通过该key值获取对象
                            Object value=mBeans.get(key);
                            //让该字段获取权限,让其可访问私有变量
                            field.setAccessible(true);
                            try { 
                                //将该service类对象设置到controller类中的autowwired字段值去
                                field.set(instance,value);
                            } catch (IllegalAccessException e) { 
                                e.printStackTrace();
                            }
                        }else { 
                            continue;
                        }
                    }
                }else { 
                    continue;
                }
            }
        }
    
        /** * @Description 实例化对象(扫描过的文件且有注解的) **/
        private void initInstance() { 
            for (String className:mClassNames){ 
                //如: com.sxkj.annotation.CustomAutowire.class 将.class后缀去掉
                String name = className.replace(".class", "");
                try { 
                    //通过文件名拿到类
                    Class<?> clazz = Class.forName(name);
                    //判断该类是否有CustomController注解类
                    if(clazz.isAnnotationPresent(CustomController.class)){ 
                        //实例化对象
                        Object instance = clazz.newInstance();
                        //获取该类上的注解的requstmapping中的value值
                        CustomRequstMapping customRequstMapping=clazz.getAnnotation(CustomRequstMapping.class);
                        mBeans.put(customRequstMapping.value(),instance);
                    } else if (clazz.isAnnotationPresent(CustomService.class)) { 
                        //实例化对象
                        Object instance = clazz.newInstance();
                        //获取该类上的注解的requstmapping中的value值
                        CustomService customService=clazz.getAnnotation(CustomService.class);
                        mBeans.put(customService.value(),instance);
                    }else { 
                        continue;
                    }
                } catch (ClassNotFoundException e) { 
                    e.printStackTrace();
                }catch (InstantiationException e) { 
                    e.printStackTrace();
                } catch (IllegalAccessException e) { 
                    e.printStackTrace();
                }
            }
        }
    
        /** * @Description 扫描文件 **/
        private void initScanFile(String basepackage) { 
            URL url = this.getClass().getClassLoader().getResource("/" + basepackage.replaceAll("\\.", "/"));
            String files = url.getFile();
            File file = new File(files);
            String[] fileList = file.list();
            for (String filePath:fileList){ 
                File filePaths = new File(files + filePath);
                if(filePaths.isDirectory()){ 
                    initScanFile(basepackage+"."+filePath);
                }else { 
                    // com.sxkj.annotation.CustomAutowire.class
                    mClassNames.add(basepackage+"."+filePaths.getName());
                }
            }
        }
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 
            doPost(req,resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest requset, HttpServletResponse response) throws ServletException, IOException { 
            //获取请求的路径
            String requestURI = requset.getRequestURI();//获取到工程名+请求路径
            //将工程名去掉,最后为请求路径 /test/getName
            String contextPath = requset.getContextPath();
            //切割后最后为请求的路径 /test/getName
            String urlPath=requestURI.replace(contextPath,"");
            //通过路径获取到mHandleUrlMapping容器中的值 method
            Method method= (Method) mHandleUrlMapping.get(urlPath);
            //通过路径 /test 获取到CustomController的实例化对象
            Object instance =  mBeans.get("/" + urlPath.split("/")[1]);
            Object[] args = handleArgs(requset, response, method);
            //执行方法
            try { 
                method.invoke(instance,args);
            } catch (IllegalAccessException e) { 
                e.printStackTrace();
            } catch (InvocationTargetException e) { 
                e.printStackTrace();
            }
    
        }
    
        private static Object[] handleArgs(HttpServletRequest request,HttpServletResponse response,Method method){ 
            //获取当前执行的方法有哪些参数
            Class<?>[] parameterTypes = method.getParameterTypes();
            //根据参数的个数,new出数组参数的数量,将方法的所有参数复制到arg[]里面来
            Object[] args = new Object[parameterTypes.length];
            int arg_i=0;int index=0;
            for (Class<?> paramClass:parameterTypes){ 
                if(ServletRequest.class.isAssignableFrom(paramClass)){ 
                    args[arg_i++]=request;
                }if(ServletResponse.class.isAssignableFrom(paramClass)){ 
                    args[arg_i++]=response;
                }
                Annotation[] annotations = method.getParameterAnnotations()[index];
                if(annotations.length>0){ 
                    for (Annotation annotation:annotations){ 
                        if(CustomRequstParam.class.isAssignableFrom(annotation.getClass())){ 
                            CustomRequstParam customRequstParam= (CustomRequstParam) annotation;
                            //获取注解里面的参数
                            args[arg_i++]=request.getParameter(customRequstParam.value());
                        }
                    }
                }
                index++;
            }
            return args;
        }
    }

##### 5.测试 #####

访问 [http://localhost:8081/test/getName?id=12][http_localhost_8081_test_getName_id_12] ,结果:

> hello,id:12

[SouthEast]: /images/20220323/75e8f6a012db4304b071377c323ae431.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTA1MjAxNDY_size_16_color_FFFFFF_t_70]: /images/20220323/453cbffec8da4aca80eaa02ee12e6fd3.png
[http_localhost_8081_test_getName_id_12]: http://localhost:8081/test/getName?id=12