自己实现简单版SpringMVC

SpringMVC的主要作用是：从http请求中得到一个url字符串和对应的请求参数，根据该字符串找到Controller中的一个方法，利用反射执行该方法，将结果返回给前端

1，初始化

　　将url请求路径和controller中的方法一一对应

　　将url请求路径和object一一对应，反射调用方法时要传入object和方法入参

2，执行请求

　　获取http请求路径和参数，找到对应的方法，执行该方法后返回给前端

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包扫描是怎么实现的

递归指定路径的目录（class文件在项目中也是放在某个目录当中的），找出所有的全局限定类名，利用反射生成该类的实例，判断该类是否有特定的注解修饰，比如说@MyController，有注解修饰的就将实例放入Map中

一，web.xml文件

<?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"  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>MVC</servlet-name>

    <servlet-class>com.irish.servlet.MyDispatcherServlet</servlet-class>

    <init-param>

      <param-name>contextConfigLocation</param-name>

      <param-value>application.properties</param-value>

    </init-param>

    <load-on-startup></load-on-startup>

  </servlet>

  <servlet-mapping>

    <servlet-name>MVC</servlet-name>

    <url-pattern>/*</url-pattern>

  </servlet-mapping>

</web-app>

二，DispathcherServlet

public class MyDispatcherServlet extends HttpServlet{

    private static final long serialVersionUID = 1L;

    private Properties properties = new Properties();

    private List<String> classNames = new ArrayList<>();

    private Map<String, Object> ioc = new HashMap<>();

    private Map<String, Method> handlerMapping = new  HashMap<>();

    private Map<String, Object> controllerMap  =new HashMap<>();

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        this.doPost(req,resp);

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        try {

            //处理请求

            doDispatch(req,resp);

        } catch (Exception e) {

            resp.getWriter().write("500!! Server Exception");

        }

    }

    private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {

        if(handlerMapping.isEmpty()){

            return;

        }

        String url =req.getRequestURI();

        String contextPath = req.getContextPath();

        System.out.println("requestUri:"+url);

        System.out.println("contextPath:"+contextPath);

        url=url.replace(contextPath, "").replaceAll("/+", "/");

        System.out.println("url:"+url);

        if(!this.handlerMapping.containsKey(url)){

            resp.getWriter().write("404 NOT FOUND!");

            return;

        }

        Method method =this.handlerMapping.get(url);

        //获取方法的参数列表

        Class<?>[] parameterTypes = method.getParameterTypes();

        //获取方法的参数列表的注解值，顺序和长度与parameterTypes相同，

        String [] paramNames = getMethodParameterNamesByAnnotation(method);

        //获取请求的参数

        Map<String, String[]> parameterMap = req.getParameterMap();

        //保存参数值

        Object [] paramValues= new Object[parameterTypes.length];

        //方法的参数列表

        for (int i = ; i<parameterTypes.length; i++){

            //根据参数名称，做某些处理

            String requestParam = parameterTypes[i].getSimpleName();

            if (requestParam.equals("HttpServletRequest")){

                //参数类型已明确，这边强转类型

                paramValues[i]=req;

                continue;

            }

            if (requestParam.equals("HttpServletResponse")){

                paramValues[i]=resp;

                continue;

            }

            if(requestParam.equals("String")){

                String theParamName = paramNames[i];

                for (Entry<String, String[]> param : parameterMap.entrySet()) {

                        if(param.getKey().equals(theParamName)) {

                             String value =Arrays.toString(param.getValue()).replaceAll("\\[|\\]", "").replaceAll(",\\s", ",");

                             //[abc, ed]  替换为  abc,ed

                             paramValues[i]=value;

                             System.out.println(theParamName  + " : "+value);

                        }

                }

            }

        }

        //利用反射机制来调用

        try {

            method.invoke(this.controllerMap.get(url), paramValues);

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    /**

     *

     * 按照方法参数的顺序获取注解的值，没有注解的参数对应的位置为空

     */

    public static String[] getMethodParameterNamesByAnnotation(Method method) {

        Annotation[][] parameterAnnotations = method.getParameterAnnotations();

        if (parameterAnnotations == null || parameterAnnotations.length == ) {

            return null;

        }

        String[] parameterNames = new String[parameterAnnotations.length];

        int i = ;

        for (Annotation[] parameterAnnotation : parameterAnnotations) {

            if(parameterAnnotation.length ==  ) {

                  parameterNames[i++] = null;

            }

            for (Annotation annotation : parameterAnnotation) {

                if (annotation instanceof MyRequestParam) {

                    MyRequestParam param = (MyRequestParam) annotation;

                    parameterNames[i++] = param.value();

                }

            }

        }

        return parameterNames;

    }

    @Override

    public void init(ServletConfig config) throws ServletException {

        //1.加载配置文件，将classpath路径下的application.properties文件加载到内存

        //config.getInitParameter("contextConfigLocation") 获取的是Servlet的配置参数

        doLoadConfig(config.getInitParameter("contextConfigLocation"));

        //2.将指定路径下的全局限定类名添加到classNames集合当中

        doScanner(properties.getProperty("scanPackage"));

        //3.通过反射实例化标注了MyController注解的类,并且放到ioc容器中

        doInstance();

        //4.初始化url和Method的对应关系，url和Object的对应关系

        initHandlerMapping();

    }

    private void  doLoadConfig(String location){

        //把web.xml中的contextConfigLocation对应value值的文件加载到流里面

        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(location);

        try {

            //用Properties文件加载文件里的内容

            properties.load(resourceAsStream);

        } catch (IOException e) {

            e.printStackTrace();

        }finally {

            //关流

            if(null!=resourceAsStream){

                try {

                    resourceAsStream.close();

                } catch (IOException e) {

                    e.printStackTrace();

                }

            }

        }

    }

    private void doScanner(String packageName) {

        //把所有的.替换成/

        URL url  =this.getClass().getClassLoader().getResource("/"+packageName.replaceAll("\\.", "/"));

        File dir = new File(url.getFile());

        for (File file : dir.listFiles()) {

            if(file.isDirectory()){

                //递归读取包

                doScanner(packageName+"."+file.getName());

            }else{

                String className =packageName +"." +file.getName().replace(".class", "");

                classNames.add(className);

            }

        }

    }

    private void doInstance() {

        if (classNames.isEmpty()) {

            return;

        }

        for (String className : classNames) {

            try {

                //把类搞出来,反射来实例化(只有加@MyController需要实例化)

                Class<?> clazz =Class.forName(className);

                if(clazz.isAnnotationPresent(MyController.class)){

                    ioc.put(toLowerFirstWord(clazz.getSimpleName()),clazz.newInstance());

                }else{

                    continue;

                }

            } catch (Exception e) {

                e.printStackTrace();

                continue;

            }

        }

    }

    private void initHandlerMapping(){

        if(ioc.isEmpty()){

            return;

        }

        try {

            for(Entry<String, Object> entry: ioc.entrySet()) {

                Class<? extends Object> clazz = entry.getValue().getClass();

                if(!clazz.isAnnotationPresent(MyController.class)){

                    continue;

                }

                //拼url时,是controller头部的url拼上方法上的url

                String baseUrl ="";

                if(clazz.isAnnotationPresent(MyRequestMapping.class)){

                    MyRequestMapping annotation = clazz.getAnnotation(MyRequestMapping.class);

                    baseUrl=annotation.value();

                }

                Method[] methods = clazz.getMethods();

                for (Method method : methods) {

                    if(!method.isAnnotationPresent(MyRequestMapping.class)){

                        continue;

                    }

                    MyRequestMapping annotation = method.getAnnotation(MyRequestMapping.class);

                    String url = annotation.value();

                    url =(baseUrl+"/"+url).replaceAll("/+", "/");

                    handlerMapping.put(url,method);

                    controllerMap.put(url,clazz.newInstance());

                    System.out.println(url+","+method);

                }

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    /**

     * 字符串首字母小写

     */

    private String toLowerFirstWord(String name){

        char[] charArray = name.toCharArray();

        charArray[] += ;

        return String.valueOf(charArray);

    }

}

三，自定义注解

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

public @interface MyController {

    /**

     * 表示给controller注册别名

     * @return

     */

    String value() default "";

}

@Target({ElementType.TYPE,ElementType.METHOD})

@Retention(RetentionPolicy.RUNTIME)

public @interface MyRequestMapping {

    /**

     * 表示访问该方法的url

     * @return

     */

    String value() default "";

}

@Target(ElementType.PARAMETER)

@Retention(RetentionPolicy.RUNTIME)

public @interface MyRequestParam {

    /**

     * 表示参数的别名，必填

     * @return

     */

    String value();

}

四，controller

@MyController

@MyRequestMapping("/test")

public class TestController {

    @MyRequestMapping("/doTest")

    public void test1(HttpServletRequest request, HttpServletResponse response,

            @MyRequestParam("param1") String param1 , @MyRequestParam("param2") String param2  ){

        System.out.println("param1 = "+ param1);

        System.out.println("param2 = "+ param2);

        try {

            response.getWriter().write( "doTest method success! param1:"+param1 + " , param2:"+ param2);

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

     @MyRequestMapping("/doTest2")

    public void test2(HttpServletRequest request, HttpServletResponse response){

        try {

            response.getWriter().println("doTest2 method success!");

        } catch (IOException e) {

            e.printStackTrace();

        }

    }

}

五，application.properties

scanPackage=com.irish.controller

六，pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.</modelVersion>

  <groupId>com.irish</groupId>

  <artifactId>mySpringMVC</artifactId>

  <version>0.0.-SNAPSHOT</version>

  <packaging>war</packaging>

     <properties>

        <project.build.sourceEncoding>UTF-</project.build.sourceEncoding>

        <maven.compiler.source>1.8</maven.compiler.source>

        <maven.compiler.target>1.8</maven.compiler.target>

        <java.version>1.8</java.version>

    </properties>

    <dependencies>

         <dependency>

           <groupId>javax.servlet</groupId>

           <artifactId>javax.servlet-api</artifactId>

           <version>3.0.</version>

           <scope>provided</scope>

        </dependency>

    </dependencies>

</project>

七，测试

项目结构

github地址 https://github.com/jake1263/MySpringMVC

巴特西

自己实现简单版SpringMVC

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