springMVC的实现原理
2019-04-28 本文已影响0人
陈柴盐
前情提要:
servlet忘了的看这个:https://www.jianshu.com/p/6c2d22b00293
反射忘了的看这个:https://www.jianshu.com/p/a15245e52a31
注解与反射结合看这个:https://www.jianshu.com/p/e8daaa56d70f
目录结构:
image.png
步骤:
1.自定义注解
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface DefineController {
String value() default "";
}
@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface DefineRequestMapping {
String value() default "";
}
2.定义Controller层
@DefineController("/test")
public class TestController {
@DefineRequestMapping("/test")
public String test(){
return "index";
}
}
3.定义Servlet(重点)
import com.demo.web.annotation.DefineController;
import com.demo.web.annotation.DefineRequestMapping;
import com.demo.web.utils.ClassUtils;
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.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
public class DefineDispatcherServlet extends HttpServlet {
//用來存放spring mvc的bean
private ConcurrentHashMap<String,Object> springMVCBeans = new ConcurrentHashMap<>();
//url與類映射
private ConcurrentHashMap<String,Object> urlBeans = new ConcurrentHashMap<>();
//url與方法映射
private ConcurrentHashMap<String,String> urlMethod = new ConcurrentHashMap<>();
/**
* 服务器启动时会读取web.xml中的servlet,自动执行Servlet的init方法
* init要完成的工作:获取含有@DefineController的类
* 获取含有@DefineRequestMapping的修饰的方法
*/
@Override
public void init() throws ServletException {
System.out.println("DefineDispatcherServlet开始初始化");
//获取包下的所有类
String packages = "com.demo.web.controller";
List<Class<?>> classList= null;
try {
classList = ClassUtils.getClassName(packages);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
//将含有@DefineController注解的类放入Map中
findAndInitMyControllerClass(classList);
//将含有@DefineRequestMapping注解的方法,根据url与方法生产Map
handlerMapping(springMVCBeans);
super.init();
}
//将含有@DefineController注解的类放入Map中
private void findAndInitMyControllerClass(List<Class<?>> classList) {
try {
for (Class c : classList){
DefineController annotation = (DefineController) c.getAnnotation(DefineController.class);
if (annotation != null){
Object o = c.newInstance();
/*获取类名首字母小写*/
String simpleName = c.getSimpleName();
String name = (simpleName.charAt(0)+"").toLowerCase()+simpleName.substring(1);
springMVCBeans.put(name, o);
}
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
// //将含有@DefineRequestMapping注解的方法,根据url与方法生产Map
private void handlerMapping(ConcurrentHashMap<String, Object> springMVCBeans) {
for (String key : springMVCBeans.keySet()){
Object o = springMVCBeans.get(key);
DefineController defineController = o.getClass().getAnnotation(DefineController.class);
Method[] methods = o.getClass().getMethods();
String url = "";
for (Method method : methods){
DefineRequestMapping defineRequestMapping = method.getAnnotation(DefineRequestMapping.class);
if (defineRequestMapping != null){
//1.拼接url
url = defineController.value() + defineRequestMapping.value();
//2.url與方法映射
urlMethod.put(url, method.getName());
}
}
//3.url與類映射
urlBeans.put(url, o);
}
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
try {
doDispatch(req,resp);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
/**
* 无论是走doGet还是走doPost最终都还是走doDispatch
* 步骤:1.获取请求的连接
* 2.获取根据连接的url从urlMethod中获取方法名
* 3.反射执行方法，这时可以从TestController中的test方法中获取到跳转地址index
* 4. 进入视图解析器
*/
private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws IOException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, ServletException{
//获取请求连接
String url = req.getRequestURI();
Object o = urlBeans.get(url); //返回值:/test/test
if (o == null) {
resp.getWriter().println("404 not found");
}
//反射执行方法
String methodName = urlMethod.get(url);
Method method = o.getClass().getMethod(methodName);
Class<?>[] parameterTypes = method.getParameterTypes();
Object result = method.invoke(o, parameterTypes);
//视图解析器
viewResolver((String) result,req,resp);
}
private void viewResolver(String pageName, HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String suffix = ".jsp";
String prefix = "/";
req.getRequestDispatcher(prefix + pageName + suffix).forward(req, resp);
}
}
ClassUtils
import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;
public class ClassUtils {
/**
* 获取某包下（包括该包的所有子包）所有类
* @param packageName 包名
* @return 类的完整名称
*/
public static List<Class<?>> getClassName(String packageName) throws ClassNotFoundException {
return getClassName(packageName, true);
}
/**
* 获取某包下所有类
* @param packageName 包名
* @param childPackage 是否遍历子包
* @return 类的完整名称
*/
public static List<Class<?>> getClassName(String packageName, boolean childPackage) throws ClassNotFoundException {
List<Class<?>> fileNames = null;
ClassLoader loader = Thread.currentThread().getContextClassLoader();
String packagePath = packageName.replace(".", "/");
URL url = loader.getResource(packagePath);
if (url != null) {
String type = url.getProtocol();
if (type.equals("file")) {
fileNames = getClassNameByFile(url.getPath(), null, childPackage);
} else if (type.equals("jar")) {
fileNames = getClassNameByJar(url.getPath(), childPackage);
}
} else {
fileNames = getClassNameByJars(((URLClassLoader) loader).getURLs(), packagePath, childPackage);
}
return fileNames;
}
/**
* 从项目文件获取某包下所有类
* @param filePath 文件路径
* @param className 类名集合
* @param childPackage 是否遍历子包
* @return 类的完整名称
*/
private static List<Class<?>> getClassNameByFile(String filePath, List<Class<?>> className, boolean childPackage) throws ClassNotFoundException {
List<Class<?>> myClassName = new ArrayList<Class<?>>();
File file = new File(filePath);
File[] childFiles = file.listFiles();
for (File childFile : childFiles) {
if (childFile.isDirectory()) {
if (childPackage) {
myClassName.addAll(getClassNameByFile(childFile.getPath(), myClassName, childPackage));
}
} else {
String childFilePath = childFile.getPath();
if (childFilePath.endsWith(".class")) {
childFilePath = childFilePath.substring(childFilePath.indexOf("\\classes") + 9, childFilePath.lastIndexOf("."));
childFilePath = childFilePath.replace("\\", ".");
myClassName.add(Class.forName(childFilePath));
}
}
}
return myClassName;
}
/**
* 从jar获取某包下所有类
* @param jarPath jar文件路径
* @param childPackage 是否遍历子包
* @return 类的完整名称
*/
private static List<Class<?>> getClassNameByJar(String jarPath, boolean childPackage) {
List<Class<?>> myClassName = new ArrayList<Class<?>>();
String[] jarInfo = jarPath.split("!");
String jarFilePath = jarInfo[0].substring(jarInfo[0].indexOf("/"));
String packagePath = jarInfo[1].substring(1);
try {
JarFile jarFile = new JarFile(jarFilePath);
Enumeration<JarEntry> entrys = jarFile.entries();
while (entrys.hasMoreElements()) {
JarEntry jarEntry = entrys.nextElement();
String entryName = jarEntry.getName();
if (entryName.endsWith(".class")) {
if (childPackage) {
if (entryName.startsWith(packagePath)) {
entryName = entryName.replace("/", ".").substring(0, entryName.lastIndexOf("."));
myClassName.add(Class.forName(entryName));
}
} else {
int index = entryName.lastIndexOf("/");
String myPackagePath;
if (index != -1) {
myPackagePath = entryName.substring(0, index);
} else {
myPackagePath = entryName;
}
if (myPackagePath.equals(packagePath)) {
entryName = entryName.replace("/", ".").substring(0, entryName.lastIndexOf("."));
myClassName.add(Class.forName(entryName));
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
return myClassName;
}
/**
* 从所有jar中搜索该包，并获取该包下所有类
* @param urls URL集合
* @param packagePath 包路径
* @param childPackage 是否遍历子包
* @return 类的完整名称
*/
private static List<Class<?>> getClassNameByJars(URL[] urls, String packagePath, boolean childPackage) {
List<Class<?>> myClassName = new ArrayList<Class<?>>();
if (urls != null) {
for (int i = 0; i < urls.length; i++) {
URL url = urls[i];
String urlPath = url.getPath();
// 不必搜索classes文件夹
if (urlPath.endsWith("classes/")) {
continue;
}
String jarPath = urlPath + "!/" + packagePath;
myClassName.addAll(getClassNameByJar(jarPath, childPackage));
}
}
return myClassName;
}
}
4.web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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>dispatcher</servlet-name>
<servlet-class>com.demo.web.servlet.DefineDispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
</web-app>
5.index.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title></title>
</head>
<body>
你好世界
</body>
</html>
6.启动与访问
image.png
过程：
启动tomcat->
加载web.xml->
通过web.xml的配置获取DefineDispatcherServlet->
执行init方法获取Controller层的类和方法以及对应的url->
用户浏览器输入url->
服务器根据用户的url获取对应的方法->
执行对应的方法结果返回需要跳转的路径->
通过视图解析器跳转到对应的连接
