通过注解实现一个简易的Spring mvc框架
1.首先我们来搭建架构，就建一个普通的javaweb项目就OK了，具体目录如下：
对于小白来说可以细看后面web.xml的配置，对javaweb有点研究可以忽略而过后面的web.xml配置。
2.先上代码，运行起整个项目。再来聊聊思路。
(1).Controller注解
package com.wuqi.annotation;
import java.lang.annotation.*;
/**
* Created by wuqi on 2017/3/22.
*/
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Controller {
String value() default "";
}
(2).Quatifier注解
package com.wuqi.annotation;
import java.lang.annotation.*;
/**
* Created by wuqi on 2017/3/25.
*/
@Target({ ElementType.FIELD }) // 代表注解的注解
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Quatifier {
String value() default "";
}
(3).RequestMapping注解
package com.wuqi.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Created by Shock on 2017/3/22.
*/
@Target({ ElementType.METHOD }) // 在方法上的注解
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RequestMapping {
String value() default "";
}
(4).Service注解
package com.wuqi.annotation;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Created by Shock on 2017/3/22.
*/
@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Service {
String value() default "";
}
--------------------------------------------------------------------------------------------------------------------------
(1).MyService接口
package com.wuqi.service.impl;
import java.util.Map;
/**
* Created by wuqi on 2017/3/23.
*/
public interface MyService {
int insert(Map map);
int delete(Map map);
int update(Map map);
int select(Map map);
}
(2).MyServiceImpl类
package com.wuqi.service.impl;
import com.wuqi.annotation.Service;
import java.util.Map;
/**
* Created by wuqi on 2017/3/23.
*/
@Service("MyServiceImpl")
public class MyServiceImpl implements MyService {
@Override
public int insert(Map map) {
System.out.println("MyServiceImpl:" + "insert");
return 0;
}
@Override
public int delete(Map map) {
System.out.println("MyServiceImpl:" + "delete");
return 0;
}
@Override
public int update(Map map) {
System.out.println("MyServiceImpl:" + "update");
return 0;
}
@Override
public int select(Map map) {
System.out.println("MyServiceImpl:" + "select");
return 0;
}
}
(3).SpringmvcService接口
package com.wuqi.service.impl;
import java.util.Map;
/**
* Created by wuqi on 2017/3/23.
*/
public interface SpringmvcService {
int insert(Map map);
int delete(Map map);
int update(Map map);
int select(Map map);
}
(4).MyServiceImpl类
package com.wuqi.service.impl;
import com.wuqi.annotation.Service;
import java.util.Map;
/**
* Created by wuqi on 2017/3/23.
*/
@Service("SpringmvcServiceImpl")
public class SpringmvcServiceImpl implements SpringmvcService{
@Override
public int insert(Map map) {
System.out.println("SpringmvcServiceImpl:" + "insert");
return 0;
}
@Override
public int delete(Map map) {
System.out.println("SpringmvcServiceImpl:" + "delete");
return 0;
}
@Override
public int update(Map map) {
System.out.println("SpringmvcServiceImpl:" + "update");
return 0;
}
@Override
public int select(Map map) {
System.out.println("SpringmvcServiceImpl:" + "select");
return 0;
}
}
--------------------------------------------------------------------------------------------------------------------------
(1).SpringmvcController类
package com.wuqi.controller;
import com.wuqi.annotation.*;
import com.wuqi.service.impl.MyService;
import com.wuqi.service.impl.SpringmvcService;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Created by wuqi on 2017/3/23.
*/
@Controller("wuqi")
public class SpringmvcController {
@Quatifier("MyServiceImpl")
MyService myService;
@Quatifier("SpringmvcServiceImpl")
SpringmvcService smService;
@RequestMapping("insert")
public String insert(HttpServletRequest request, HttpServletResponse response, String param) {
myService.insert(null);
smService.insert(null);
return null;
}
@RequestMapping("delete")
public String delete(HttpServletRequest request, HttpServletResponse response, String param) {
myService.delete(null);
smService.delete(null);
return null;
}
@RequestMapping("update")
public String update(HttpServletRequest request, HttpServletResponse response, String param) {
myService.update(null);
smService.update(null);
return null;
}
@RequestMapping("select")
public String select(HttpServletRequest request, HttpServletResponse response, String param) {
myService.select(null);
smService.select(null);
return null;
}
}
--------------------------------------------------------------------------------------------------------------------------
(1).DispatcherServlet类继承 javax.servlet.http.HttpServlet类
package com.wuqi.servlet;
import com.wuqi.annotation.*;
import com.wuqi.controller.SpringmvcController;
import java.io.File;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Created by Shock on 2017/3/23.
*/
public class DispatcherServlet extends HttpServlet{
private static final long serialVersionUID = 1L;
List<String> packageNames = new ArrayList<String>();
// 所有类的实例，key是注解的value,value是所有类的实例
Map<String, Object> instanceMap = new HashMap<String, Object>();
Map<String, Object> handerMap = new HashMap<String, Object>();
public DispatcherServlet() {
super();
}
public void init(ServletConfig config) throws ServletException {
// 包扫描,获取包中的文件
scanPackage("com.wuqi");
try {
filterAndInstance();
} catch (Exception e) {
e.printStackTrace();
}
// 建立映射关系
handerMap();
// 实现注入
ioc();
}
private void filterAndInstance() throws Exception {
if (packageNames.size() <= 0) {
return;
}
for (String className : packageNames) {
Class<?> cName = Class.forName(className.replace(".class", "").trim());
if (cName.isAnnotationPresent(Controller.class)) {
Object instance = cName.newInstance();
Controller controller = (Controller) cName.getAnnotation(Controller.class);
String key = controller.value();
instanceMap.put(key, instance);
} else if (cName.isAnnotationPresent(Service.class)) {
Object instance = cName.newInstance();
Service service = (Service) cName.getAnnotation(Service.class);
String key = service.value();
instanceMap.put(key, instance);
} else {
continue;
}
}
}
private void ioc() {
if (instanceMap.isEmpty())
return;
for (Map.Entry<String, Object> entry : instanceMap.entrySet()) {
// 拿到里面的所有属性
Field fields[] = entry.getValue().getClass().getDeclaredFields();
for (Field field : fields) {
field.setAccessible(true);// 可访问私有属性
if (field.isAnnotationPresent(Quatifier.class));
Quatifier quatifier = field.getAnnotation(Quatifier.class);
String value = quatifier.value();
field.setAccessible(true);
try {
field.set(entry.getValue(), instanceMap.get(value));
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
SpringmvcController wuqi = (SpringmvcController) instanceMap.get("wuqi");
System.out.print(wuqi);
}
/**
* 扫描包下的所有文件
*
* @param Package
*/
private void scanPackage(String Package) {
URL url = this.getClass().getClassLoader().getResource("/" + replaceTo(Package));// 将所有的.转义获取对应的路径
String pathFile = url.getFile();
File file = new File(pathFile);
String fileList[] = file.list();
for (String path : fileList) {
File eachFile = new File(pathFile + path);
if (eachFile.isDirectory()) {
scanPackage(Package + "." + eachFile.getName());
} else {
packageNames.add(Package + "." + eachFile.getName());
}
}
}
/**
* 建立映射关系
*/
private void handerMap() {
if (instanceMap.size() <= 0)
return;
for (Map.Entry<String, Object> entry : instanceMap.entrySet()) {
if (entry.getValue().getClass().isAnnotationPresent(Controller.class)) {
Controller controller = (Controller) entry.getValue().getClass().getAnnotation(Controller.class);
String ctvalue = controller.value();
Method[] methods = entry.getValue().getClass().getMethods();
for (Method method : methods) {
if (method.isAnnotationPresent(RequestMapping.class)) {
RequestMapping rm = (RequestMapping) method.getAnnotation(RequestMapping.class);
String rmvalue = rm.value();
handerMap.put("/" + ctvalue + "/" + rmvalue, method);
} else {
continue;
}
}
} else {
continue;
}
}
}
private String replaceTo(String path) {
return path.replaceAll("\\.", "/");
}
@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 url = req.getRequestURI();
String context = req.getContextPath();
String path = url.replace(context, "");
Method method = (Method) handerMap.get(path);
SpringmvcController controller = (SpringmvcController) instanceMap.get(path.split("/")[1]);
try {
method.invoke(controller, new Object[] { req, resp, null });
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}
}
所有的代码已经贴上，还有个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_1.xsd"
version="3.1">
<servlet>
<servlet-name>testServlet</servlet-name>
<servlet-class>com.wuqi.servlet.DispatcherServlet</servlet-class>
</servlet>
<!-- ... -->
<servlet-mapping>
<servlet-name>testServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
</web-app>
3.好了代码已经贴上了，现在需要来说说思路，因为有代码了，所以用代码来将思路，这样更容易理解代码的含义。之后可以根据自己的程度去试着写。
- 首先我们需要扫描包中的所有文件（DispatcherServlet -> init(ServletConfig config) -> scanPackage("com.wuqi")），也就是含有注解的文件。然后将该包下的所有文件都存入packageNames集合中。
- 这时我们拿到了包下所有的文件，但我们只需要含有我们指定注解的那部分文件，因此需要过滤出我们想要的文件即可，并且在过滤的过程中，我们可以将过滤出来的类通过Class.forName来直接实例化并储存起来。存放到instanceMap集合中，并为其设置对应的key值，该key值就是类注解的value。
- 然后遍历instanceMap集合中的所有对象，获取指定注解的对象，并通过反射获取该对象的所有的方法，遍历所有的方法，将指定注解的方法存入handerMap，key为拼接字符串（"/" + 对象变量名 + "/" + 方法名），value为方法（Method）。
- 然后我们可以遍历instanceMap集合中的所有对象，通过反射获取对象的所有属性值（字段）集合，然后遍历属性值集合，将属性值含有指定注解的，通过Field的set方法为该属性值赋值，这时就将对象注入了。（也就是往Controller中注入Service对象）
- 最后就可以通过反射的invoke方法调用某个对象的某个方法。（此时对象存于instanceMap，而方法都存于handerMap）
参考链接：
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