作爲java程序員，項目中使用到的主流框架多多少少和spring有關聯，在面試的過程難免會問一些spring springmvc spring boot的東西，比如設計模式的使用、 怎麼實現springioc 怎麼實現springmvc諸如此類的問題，今天我們就來探尋spring mvc的實現，然後自己實現一個簡單的spring mvc
一. 瞭解spring mvc的基本運行流程
ps: 網上一大堆關於springmvc的詳細講解，在這裏就不累贅了
小結：spring mvc的核心是DispatcherServlet，DispatcherServlet繼承於HttpServlet，可以說spring mvc是基於Servlet的一個實現，DispatcherServlet負責協調和組織不同組件以完成請求處理並返回響應的工作，實現了MVC模式。
二. 梳理簡單SpringMVC的設計思路
1. 初始化容器
1.1 讀取配置文件
1.1.1.加載配置文件信息到DispatcherServlet
1.2 根據配置掃描包、初始化容器和組件
1.2.1.根據配置信息遞歸掃描包
1.2.2.把包下的類實例化 並且掃描註解
1.2.3.根據類的方法和註解，初始化HandlerMapping
2. 處理業務請求
2.1 處理請求業務
2.2.1 首先拿到請求URI
2.2.2 根據URI，在HandlerMapping中查找和URI對應的Handler
2.2.3 根據Handler裏面的method中的參數名稱和http中的請求參數匹配，填充method參數，反射調用
三. 沒時間解釋了，快上車
ps ：環境基於maven idea tomat（端口8080） servlet
1.搭建一個基本web項目，並導入idea配置servlet 和javassist pom依賴 如下
創建命令: mvn archetype:generate -DgroupId=com.adminkk -DartifactId=adminkk-mvc -DpackageName=com.adminkk -Dversion=1.0
pom依賴
<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>4.0.0</modelVersion> <groupId>com.adminkk</groupId> <artifactId>adminkk-mvc</artifactId> <version>1.0-SNAPSHOT</version> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>8</source> <target>8</target> </configuration> </plugin> </plugins> </build> <packaging>war</packaging> <name>adminkk-mvc</name> <url>http://maven.apache.org</url> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> </properties> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> <!--servlet--> <dependency> <groupId>javax.servlet</groupId> <artifactId>javax.servlet-api</artifactId> <version>3.0.1</version> <scope>provided</scope> </dependency> <!-- asm --> <dependency> <groupId>asm</groupId> <artifactId>asm</artifactId> <version>3.3.1</version> </dependency> <!-- javassist --> <dependency> <groupId>org.javassist</groupId> <artifactId>javassist</artifactId> <version>3.23.1-GA</version> </dependency> </dependencies></project>
2.創建mvc的註解 Controller RequestMapping 和統一異常處理類、方法參數工具類ParameterNameUtils
package com.adminkk.annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)public @interface Controller { public String value() default ""; public String description() default "";
}package com.adminkk.annotation;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target({ElementType.TYPE,ElementType.METHOD})@Retention(RetentionPolicy.RUNTIME)public @interface RequestMapping { public String value() default ""; public String method() default ""; public String description() default "";
}package com.adminkk.exception;
public final class MvcException extends RuntimeException{
public MvcException() { super();
}
public MvcException(String message) { super(message);
}
}package com.adminkk.tools;import javassist.*;import javassist.bytecode.CodeAttribute;import javassist.bytecode.LocalVariableAttribute;import javassist.bytecode.MethodInfo;import java.lang.reflect.Method;
public final class ParameterNameUtils {
public final static String[] getParameterNamesByJavassist(final Class<?> clazz, final Method method) {
ClassPool pool = ClassPool.getDefault(); try {
CtClass ctClass = pool.get(clazz.getName());
CtMethod ctMethod = ctClass.getDeclaredMethod(method.getName()); // 使用javassist的反射方法的參數名
MethodInfo methodInfo = ctMethod.getMethodInfo();
CodeAttribute codeAttribute = methodInfo.getCodeAttribute();
LocalVariableAttribute attr = (LocalVariableAttribute) codeAttribute
.getAttribute(LocalVariableAttribute.tag); if (attr != null) { String[] rtv = new String[ctMethod.getParameterTypes().length]; int len = ctMethod.getParameterTypes().length; // 非靜態的成員函數的第一個參數是this
int pos = Modifier.isStatic(ctMethod.getModifiers()) ? 0 : 1; for (int i = 0; i < len; i++) {
rtv[i] = attr.variableName(i + pos);
} return rtv;
}
} catch (NotFoundException e) {
System.out.println("獲取異常"+ e.getMessage());
} return new String[0];
}
}3.創建 HandlerMapping類 主要是兩個方法 doInit初始化 doService處理請求 相關代碼如下
package com.adminkk.handler;import com.adminkk.scan.FileScaner;import com.adminkk.scan.Scaner;import com.adminkk.scan.XmlScaner;import com.adminkk.tools.ParameterNameUtils;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.PrintWriter;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;
public final class HandlerMapping {
private static final Map<String,Handler> handlerMapping = new HashMap<String, Handler>();
private static final List<Scaner> scaners = new ArrayList<>(2); static {
scaners.add(new XmlScaner());
scaners.add(new FileScaner());
}
public static void scanPackage(String scanUrl) throws RuntimeException, IllegalAccessException, InstantiationException, ClassNotFoundException { for (Scaner scaner : scaners) {
scaner.doScane(scanUrl);
}
}
public static void doInit(String scanUrl) throws IllegalAccessException, ClassNotFoundException, InstantiationException {
scanPackage(scanUrl);
}
public static void doService(HttpServletRequest request, HttpServletResponse response) { String requestURI = request.getRequestURI();
System.out.println("請求地址是="+ requestURI);
Handler handler = handlerMapping.get(requestURI); if(handler == null){
System.out.println("請求地址是="+ requestURI+" 沒有配置改路徑"); return;
}
Method method = handler.getMethod(); Object instance = handler.getInstance();
response.setCharacterEncoding("UTF-8"); //response.setContentType("application/json; charset=utf-8");
PrintWriter writer = null; try { //這裏是簡單的解析 可以像springmvc那樣解析處理
Map<String, String[]> parameterMap = request.getParameterMap(); String[] parameters = ParameterNameUtils.getParameterNamesByJavassist(instance.getClass(),method); Object[] parameter = new Object[parameters.length]; if(parameters != null && parameters.length > 0){ for (int i = 0; i < parameters.length; i++) { final String simpleName = parameters[i];
StringBuilder parameterSb = new StringBuilder(); final String[] parameterStr = parameterMap.get(simpleName); if(parameterStr != null){ for (int j = 0; j < parameterStr.length; j++) {
parameterSb.append(parameterStr[j]);
}
}
parameter[i] = parameterSb.toString();
}
}
writer = response.getWriter(); String result = (String) method.invoke(instance,parameter);
writer.print(result);
} catch (Exception e) {
e.printStackTrace();
System.out.println("請求地址是="+ requestURI+" 執行異常");
writer.print("業務執行異常");
}finally {
writer.flush();
writer.close();
}
}
public static Handler addHandlerMapping(String url,Handler handler) { return handlerMapping.put(url,handler);
}
public static Handler getHandlerMapping(String url) { return handlerMapping.get(url);
}
}掃描包
package com.adminkk.scan;public interface Scaner { void doScane(String scanUrl) throws IllegalAccessException, InstantiationException, ClassNotFoundException;
}package com.adminkk.scan;import com.adminkk.exception.MvcException;import com.adminkk.factory.BeanPostProcessor;import com.adminkk.factory.MvcBeanPostProcessor;import com.adminkk.factory.ServiceBeanPostProcessor;import com.adminkk.handler.HandlerMapping;import javassist.ClassClassPath;import javassist.ClassPool;import java.io.File;import java.util.ArrayList;import java.util.List;public final class FileScaner implements Scaner{ public FileScaner() {
} public static final List<BeanPostProcessor> beanPostProcessorList = new ArrayList<>(); static {
beanPostProcessorList.add(new MvcBeanPostProcessor());
beanPostProcessorList.add(new ServiceBeanPostProcessor());
}
@Override public void doScane(String scanUrl) throws IllegalAccessException, InstantiationException, ClassNotFoundException { if(scanUrl == null || scanUrl.length() == 0){ throw new MvcException("容器基礎掃描路徑爲空，請檢查參數配置");
}
String baseUrl = HandlerMapping.class.getResource("/").getPath();
String codeUrl = scanUrl.replaceAll("\\.", "/");
String path = baseUrl + codeUrl; File file = new File(path); if(file == null || !file.exists()){ throw new MvcException("找不到對應掃描路徑，請檢查參數配置");
}
recursionRedFile(scanUrl,file);
} //遞歸讀取文件
private void recursionRedFile(String scanUrl,File file) throws MvcException, ClassNotFoundException, IllegalAccessException, InstantiationException { if(!file.exists()){ return;
} //讀取java文件
if(file.isFile()){
String beanName = scanUrl.replaceAll(".class",""); Class<?> forName = Class.forName(beanName); //放到Javassist容器裏面
ClassPool pool = ClassPool.getDefault();
ClassClassPath classPath = new ClassClassPath(forName);
pool.insertClassPath(classPath); if(forName.isAnnotation() || forName.isEnum() || forName.isInterface() ){ return;
}
Object newInstance = forName.newInstance(); //前置執行
for (int i = 0; i < beanPostProcessorList.size() ; i++) {
BeanPostProcessor beanPostProcessor = beanPostProcessorList.get(i);
beanPostProcessor.postProcessBeforeInitialization(newInstance,beanName);
} //後置執行
for (int i = beanPostProcessorList.size()-1; i > 0 ; i++) {
BeanPostProcessor beanPostProcessor = beanPostProcessorList.get(i);
beanPostProcessor.postProcessAfterInitialization(newInstance,beanName);
} return;
} //文件夾下面的文件都遞歸處理
if(file.isDirectory()){ File[] files = file.listFiles(); if(files != null && files.length >0){ for (int i = 0; i < files.length; i++) { File targetFile = files[i];
recursionRedFile(scanUrl+"."+targetFile.getName(),targetFile);
}
}
}
}
}package com.adminkk.scan;public final class XmlScaner implements Scaner{ public XmlScaner() {
} @Override
public void doScane(String scanUrl) { //可自行擴展
}
}掃描bean
package com.adminkk.factory;import com.adminkk.exception.MvcException;
public interface BeanPostProcessor { Object postProcessBeforeInitialization(Object object, String beanName) throws MvcException; Object postProcessAfterInitialization(Object object, String beanName) throws MvcException;
}package com.adminkk.factory;import com.adminkk.annotation.Controller;import com.adminkk.annotation.RequestMapping;import com.adminkk.exception.MvcException;import com.adminkk.handler.Handler;import com.adminkk.handler.HandlerMapping;import java.lang.reflect.Method;
public class MvcBeanPostProcessor implements BeanPostProcessor{ //掃描Controller業務
@Override
public Object postProcessBeforeInitialization(Object object, String beanName) throws MvcException {
Class<?> objectClass = object.getClass(); if(objectClass.getAnnotation(Controller.class) != null){
RequestMapping cal***equestMappingAnnotation = objectClass.getAnnotation(RequestMapping.class);
StringBuilder urlSb = new StringBuilder(); if(cal***equestMappingAnnotation != null){
urlSb.append(cal***equestMappingAnnotation.value());
}
Method[] methods = objectClass.getMethods(); if(methods != null && methods.length > 0 ){ for (int i = 0; i < methods.length; i++) {
Method method = methods[i];
RequestMapping methodAnnotation = method.getAnnotation(RequestMapping.class); if(methodAnnotation != null){ String methodValue = methodAnnotation.value(); String url = new StringBuilder().append(urlSb).append(methodValue).toString();
Handler handler = HandlerMapping.getHandlerMapping(url); if(handler == null){
handler = new Handler();
handler.setMethod(method);
handler.setInstance(object);
HandlerMapping.addHandlerMapping(url,handler);
}else { throw new MvcException("請求路徑"+ url + "已經存在容器中");
}
}
}
}
} return object;
} @Override
public Object postProcessAfterInitialization(Object object, String beanName) throws MvcException { return null;
}
}package com.adminkk.factory;import com.adminkk.exception.MvcException;public class ServiceBeanPostProcessor implements BeanPostProcessor { @Override
public Object postProcessBeforeInitialization(Object object, String beanName) throws MvcException { //可自行擴展
return null;
} @Override
public Object postProcessAfterInitialization(Object object, String beanName) throws MvcException { //可自行擴展
return null;
}
}5.創建 DispatcherServlet
package com.adminkk.servlet;import com.adminkk.handler.HandlerMapping;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;@WebServlet(name = "DispatcherServlet",loadOnStartup=1,urlPatterns={"/"})public final class DispatcherServlet extends HttpServlet { public static final String BASE_SCAN_URL = "com.adminkk"; //初始化容器
@Override
public void init() throws ServletException {
doInit();
} //處理業務請求
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doService(req,resp);
} private void doService(HttpServletRequest req, HttpServletResponse resp) throws ServletException { try {
HandlerMapping.doService(req,resp);
}catch (Exception e){
e.printStackTrace(); throw new ServletException(e.getMessage());
}
} private void doInit() throws ServletException { try {
HandlerMapping.doInit(this.BASE_SCAN_URL);
}catch (Exception e){
e.printStackTrace(); throw new ServletException(e.getMessage());
}
}
}好了，目前爲止我們就寫好了簡版的springmvc 下面開始測試
package com.adminkk.controller;import com.adminkk.annotation.Controller;import com.adminkk.annotation.RequestMapping;@Controller@RequestMapping("/mvc")public class MvcController { @RequestMapping("/index")
public String index(){ return "adminkk-mvc system is running";
} @RequestMapping("/arg")
public String parameter(String argOne, String argTwo){ return "argOne = " + argOne + " argTwo = " + argTwo;
}
}訪問地址 http://localhost:8080/mvc/index
訪問地址: http://localhost:8080/mvc/arg?argOne=argOne&argTwo=argTwo
總結 ：整體實現簡單的springmvc，設計上還可以擴展更多，難點在於method 獲取方法上的參數名稱，由於jdk1.8以前是不支持的，需要借用第三方工具 比如 asm javassist黑科技工具包來幫助實現，spring-core使用的是LocalVariableTableParameterNameDiscoverer底層是調用asm,我們這裏使用的是javassist。延用這套思路還可以和spring項目結合，寫一個 基於spring的springmvc項目