手写spring mvc底层源码

手写源码之前先来了解几个概念：

1、spring IOC：控制反转，简单来说，就是tomcat在运行得时候创建了一个map，将那些有注解的对象存入这个map中，然后通过注解来获取这些对象供程序使用

2、DI：依赖注入，动态的向某个对象提供它需要的对象

3、DispatcherServlet：Spring MVC底层的具体实现，一般我们会选择默认提供的org.springframework.web.servlet.DispatcherServlet

 

如果想自己实现底层源码，那么就得自己手写DisPatcherServlet

1、首先自己定义几个注解，例如：

@Target(java.lang.annotation.ElementType.FIELD)//只能在类属性上使用

@Retention(RetentionPolicy.RUNTIME)//运行时调用

@Documented

public @interface TestAutowired {

String value() default "";

}

 

@Target(java.lang.annotation.ElementType.TYPE)//只能在类上使用

@Retention(RetentionPolicy.RUNTIME)//运行时调用

@Documented

public @interface TestController {

String value() default "";

}

 

@Target({java.lang.annotation.ElementType.TYPE,java.lang.annotation.ElementType.METHOD})//只能在类、方法上使用

@Retention(RetentionPolicy.RUNTIME)//运行时调用

@Documented

public @interface TestRequestMapping {

String value() default "";

}

 

@Target(java.lang.annotation.ElementType.PARAMETER)//只能在方法上使用

@Retention(RetentionPolicy.RUNTIME)//运行时调用

@Documented

public @interface TestRequestParam {

String value() default "";

}

 

@Target(java.lang.annotation.ElementType.TYPE)//只能在类上使用

@Retention(RetentionPolicy.RUNTIME)//运行时调用

@Documented

public @interface TestService {

String value() default "";

}

 

2、自己手写DispatcherServlet

public class DispatcherServlet extends HttpServlet{

 

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

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

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

 

@Override

public void init(ServletConfig servletConfig) throws ServletException {

//1、扫描

scanPackage("com.wzy");

//2、实例化

doInstance();

//3、自动注入

doAutowired();

//4、方法映射，路径与方法对应

doUrlMapping();

}

 

public void doUrlMapping() {

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

Object instance = entry.getValue();

Class<?> clazz = instance.getClass();

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

//获取类的上的请求路径

TestRequestMapping classMapping = clazz.getAnnotation(TestRequestMapping.class);

String classPath = classMapping.value();

Method[] methods = clazz.getMethods();

for(Method method : methods) {

if(method.isAnnotationPresent(TestRequestMapping.class)) {

TestRequestMapping methodMapping= method.getAnnotation(TestRequestMapping.class);

String methodPath = methodMapping.value();

handlerMap.put(classPath+methodPath, method);

}

}

}

}

}

 

public void doAutowired() {

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

Object instance = entry.getValue();

Class<?> clazz = instance.getClass();

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

Field[] fields = clazz.getDeclaredFields();

for(Field field : fields) {

if(field.isAnnotationPresent(TestAutowired.class)) {

TestAutowired testAutowired = field.getAnnotation(TestAutowired.class);

String key = testAutowired.value();

Object obj = beans.get(key);

if(obj != null) {

//打开权限

field.setAccessible(true);

try {

field.set(instance, obj);

} catch (IllegalArgumentException e) {

e.printStackTrace();

} catch (IllegalAccessException e) {

e.printStackTrace();

}

}else {

throw new RuntimeException(obj.getClass().getName()+"was not injection!");

}

}else {

continue;

}

}

}else {

continue;

}

}

}

 

public void doInstance() {

for(String className : classNames) {

String cn = className.replace(".class", "");

try {

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

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

//创建实例

Object instance = clazz.newInstance();

TestRequestMapping m1 = clazz.getAnnotation(TestRequestMapping.class);

beans.put(m1.value(), instance);

}else if(clazz.isAnnotationPresent(TestService.class)) {

//创建实例

Object instance = clazz.newInstance();

TestService m2 = clazz.getAnnotation(TestService.class);

beans.put(m2.value(), instance);

}else {

continue;

}

} catch (ClassNotFoundException e) {

e.printStackTrace();

} catch (InstantiationException e) {

e.printStackTrace();

} catch (IllegalAccessException e) {

e.printStackTrace();

}

}

}

 

public void scanPackage(String basePackage) {

//查找类的路径

URL url = this.getClass().getClassLoader().getResource(

"/"+basePackage.replaceAll("\\.", "/"));

String fileStr = url.getFile();

File file = new File(fileStr);

String[] filesStr = file.list();

for(String path : filesStr) {

File filePath = new File(fileStr+path);

if(filePath.isDirectory()) {

scanPackage(basePackage+"."+path);

}else {

classNames.add(basePackage+"."+filePath.getName());

}

}

}

 

 

@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 {

String uri = req.getRequestURI();

String context = req.getContextPath();

String path = uri.replace(context, "");

Method method = (Method) handlerMap.get(path);

TestController instance = (TestController) beans.get("/"+path.split("/")[1]);

Object[] args = hand(req, resp, method);

try {

method.invoke(instance, args);

} catch (IllegalAccessException e) {

e.printStackTrace();

} catch (IllegalArgumentException e) {

e.printStackTrace();

} catch (InvocationTargetException e) {

e.printStackTrace();

}

}

 

private static Object[] hand(HttpServletRequest request, HttpServletResponse response, Method method) {

//拿到当前待执行的方法有哪些参数

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

//根据参数的个数，new 一个参数的数组，将方法里的所有参数赋值到args来

Object[] args = new Object[paramClazzs.length];

int arg_i = 0;

int index = 0;

for(Class<?> paramClazz : paramClazzs) {

if(ServletRequest.class.isAssignableFrom(paramClazz)) {

args[arg_i++] = request;

}

if(ServletResponse.class.isAssignableFrom(paramClazz)) {

args[arg_i++] = response;

}

//判断有没有RequestParam注释

Annotation[] paramAns = method.getParameterAnnotations()[index];

if(paramAns.length > 0) {

for(Annotation annotation : paramAns) {

if(TestRequestParam.class.isAssignableFrom(paramAns.getClass())) {

TestRequestParam rp = (TestRequestParam) annotation;

args[arg_i++] = request.getParameter(rp.value());

}

}

}

index ++;

}

return args;

}

 

}

具体讲解下：

scanPackage方法，主要是遍历当前项目，将当前项目中的所有类都存于map中

doInstance方法，主要是遍历上述所有类，将类上有@TestController和@TestService的类进行实例化，然后存于另外的map中，key取@TestRequestMapping后的value值

doAutowired方法，主要是将所有带有@TestController类中的属性上带有@TestAutowired的这些属性从之前的map中获取实例，放进当前的属性中

doUrlMapping方法，将所有@TestController中方法上带有@TestRequestMapping的跟注解后的value路径进行对应

hand，获取当前请求对应的方法中有哪些参数

 

注意：本文没有提到其实在@TestService注解的类下其实也可有@TestAutoWired注解的属性，这个其实可以根据上面的逻辑进行扩展;还有当某个注解后没有value属性值的话，key值该怎么取，可以先获取当前类、属性的名称，然后将首字母小写，将其作为key就可以了

 

附上本人练习项目控制层和服务层：

@TestController

@TestRequestMapping("/test")

public class OrderController {

 

@TestAutowired("orderServiceImpl")

private OrderService orderService;

 

@TestRequestMapping("/get")

public String get(@TestRequestParam("name")String name, @TestRequestParam("age")int age) {

return orderService.query(name, age);

}

 

}

 

@TestService("orderServiceImpl")

public class OrderServiceImpl implements OrderService{

 

public String query(String name, int age) {

return "[name:"+name+",age"+age+"]";

}

 

}

 转发表明来源