Spring MVC流程
Spring MVC流程
步骤
- 前端控制器DispatcherServlet接收HTTP请求
- 控制器通过处理器映射器HandlerMapping找到并返回执行链HandlerExecutionChain
- 控制器调用处理器适配器HandlerAdapter去执行处理器，执行完成后返回ModelAndView给控制器
- 控制器请求视图解析器去资源定位，视图解析
- 控制器对视图进行数据渲染
github
手撸一个超简版springmvc
撸一个简单的Spring MVC框架
定义两个基本注解-@Controller和@RequestMapping
package com.bpf.mvc.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* 标识一个类为控制器
*/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Controller {
}
package com.bpf.mvc.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* 标识控制器或其内部方法的请求映射
*/
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestMapping {
/**
* url请求路径
* @return
*/
String value();
}
定义一个包扫描类
package com.bpf.mvc.util;
import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
/**
* 扫描指定包下的类
*/
public class ClassScanner {
public static Map<String, Class<?>> scannerClass(String basePackage) {
Map<String, Class<?>> result = new HashMap<>();
//通过包名将.替换成/
String filePath = basePackage.replace(".", "/");
//通过类加载器获取完整路径
try {
//获取字节码文件的位置
Enumeration<URL> dirs = Thread.currentThread().getContextClassLoader().getResources(filePath);
while (dirs.hasMoreElements()) {
URL url = dirs.nextElement();
//判断是否是文件
if (url.getProtocol().equals("file")) {
String realPath = url.getPath().substring(1);
File file = new File(realPath);
scannerFile(file, realPath.substring(realPath.lastIndexOf(filePath)), result);
}
}
} catch (IOException e) {
e.printStackTrace();
}
return result;
}
private static void scannerFile(File folder, String realPath, Map<String, Class<?>> classes) {
File[] files = folder.listFiles();
for (int i = 0; files != null && i < files.length; i ++) {
File file = files[i];
if (file.isDirectory()) {
//递归查找指定路径下的所有class字节码文件
scannerFile(file, realPath + file.getName() + "/", classes);
} else {
//class文件的绝对路径
String path = file.getAbsolutePath();
if (path.endsWith(".class")) {
path = path.replace("\\", "/");
String className = realPath + path.substring(path.lastIndexOf("/") + 1, path.indexOf(".class"));
//获取类名称 eg:com.bpf.mvc.annotation.Controller
className = className.replace("/", ".");
try {
classes.put(className, Class.forName(className));
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}
}
}
}
定义一个DispatcherServlet
package com.bpf.mvc;
import com.bpf.mvc.annotation.Controller;
import com.bpf.mvc.annotation.RequestMapping;
import com.bpf.mvc.util.ClassScanner;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
/**
* 前端控制器
*/
@WebServlet(urlPatterns = "*.htm", initParams = @WebInitParam(name = "basePackage", value = "com.bpf.mvc"))
public class DispatcherServlet extends HttpServlet {
/**
* 保存类名和对象的映射
*/
private Map<String, Object> controllers = new HashMap<>();
/**
* 保存url和方法的映射
*/
private Map<String, Method> methods = new HashMap<>();
@Override
public void init(ServletConfig config) throws ServletException {
String basePackage = config.getInitParameter("basePackage");
Map<String, Class<?>> classMap = ClassScanner.scannerClass(basePackage);
for (Map.Entry<String, Class<?>> kv : classMap.entrySet()) {
String className = kv.getKey();
Class<?> clazz = kv.getValue();
//获取@Controller以及@RequestMapping标记的内容
if (clazz.isAnnotationPresent(Controller.class)) {
String path = "";
if (clazz.isAnnotationPresent(RequestMapping.class)) {
RequestMapping rqm = clazz.getAnnotation(RequestMapping.class);
path = rqm.value().startsWith("/") ? rqm.value() : "/" + rqm.value();
}
try {
controllers.put(className, clazz.newInstance());
} catch (InstantiationException | IllegalAccessException e) {
e.printStackTrace();
}
Method[] ms = clazz.getMethods();
for (Method m : ms) {
if (!m.isAnnotationPresent(RequestMapping.class)) {
continue;
}
String url = m.getAnnotation(RequestMapping.class).value();
url = url.startsWith("/") ? url : "/" + url;
methods.put(path + url, m);
}
}
}
}
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String uri = req.getRequestURI();
String contextPath = req.getContextPath();
String mappingPath = uri.substring(uri.lastIndexOf(contextPath) + contextPath.length());
Method method = methods.get(mappingPath);
Object controller = controllers.get(method.getDeclaringClass().getName());
try {
method.invoke(controller);
} catch (IllegalAccessException | InvocationTargetException e) {
e.printStackTrace();
}
}
}
测试
package com.bpf.mvc.controller;
import com.bpf.mvc.annotation.Controller;
import com.bpf.mvc.annotation.RequestMapping;
@Controller
public class HelloController {
@RequestMapping("hello.htm")
public void hello() {
System.out.println("hello");//请求接口控制台打印hello
}
@RequestMapping("world.htm")
public void world() {
System.out.println("world");//请求接口控制台打印world
}
}
总结
demo主要实现了通过请求url调用方法的过程，并没有实现视图解析渲染相关操作，有能力者可以自行扩展
