簡介

以前用了下SpringMVC感覺挺不錯了，前段事件也簡單了寫了一些代碼來實現了SpringMVC簡單的請求分發功能，實現的主要思想如下：

將處理請求的類在系統啓動的時候加載起來，相當於SpringMVC中的Controller
讀取Controller中的配置並對應其處理的URL
通過調度Servlet進行攔截請求，並找到相應的Controller進行處理

主要代碼

首先得標識出來哪些類是Controller類，這裏我自己定義的是ServletHandler，通過Annotation的方式進行標識，並配置每個類和方法處理的URL：

package com.meet58.base.servlet.annotation;
public @interface ServletHandler {
}

package com.meet58.base.servlet.annotation;

public @interface ServletHandler {
	
}

這裏註解主要是聲明這個類是一個ServletHandler類，用於處理請求的類，系統啓動的時候就會加載這些類。

[java] view plain copy print ?

package com.meet58.base.servlet.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;
import com.meet58.base.servlet.types.RequestMethod;
import com.meet58.base.servlet.types.ResponseType;
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface HandlerMapping {
String value();
}

package com.meet58.base.servlet.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;

import com.meet58.base.servlet.types.RequestMethod;
import com.meet58.base.servlet.types.ResponseType;

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface HandlerMapping {
	String value();	
	
}

這個註解是配置處理請求的註解，定義了要處理的路徑。

定義了註解之後就是要在系統啓動的時候掃描並加載這些類，下面是如何進行掃描的代碼：

[java] view plain copy print ?

package com.meet58.base.servlet.mapping;
import java.io.IOException;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternUtils;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.core.type.filter.AnnotationTypeFilter;
import org.springframework.core.type.filter.TypeFilter;
import org.springframework.util.ClassUtils;
import com.meet58.base.servlet.annotation.ServletHandler;
public class ServletHandlerMappingResolver {
private static final String RESOURCE_PATTERN = "/**/*.class";
private String[] packagesToScan;
private ResourcePatternResolver resourcePatternResolver;
private static final TypeFilter[] ENTITY_TYPE_FILTERS = new TypeFilter[] {
new AnnotationTypeFilter(ServletHandler.class, false)};
public ServletHandlerMappingResolver(){
this.resourcePatternResolver = ResourcePatternUtils.getResourcePatternResolver(new PathMatchingResourcePatternResolver());
}
public ServletHandlerMappingResolver scanPackages(String[] packagesToScan){
try {
for (String pkg : packagesToScan) {
String pattern = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
ClassUtils.convertClassNameToResourcePath(pkg) + RESOURCE_PATTERN;
Resource[] resources;
resources = this.resourcePatternResolver.getResources(pattern);
MetadataReaderFactory readerFactory = new CachingMetadataReaderFactory(this.resourcePatternResolver);
for (Resource resource : resources) {
if (resource.isReadable()) {
MetadataReader reader = readerFactory.getMetadataReader(resource);
String className = reader.getClassMetadata().getClassName();
if (matchesFilter(reader, readerFactory)) {
ServletHandlerMappingFactory.addClassMapping(this.resourcePatternResolver.getClassLoader().loadClass(className));
}
}
}
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return this;
}
public String[] getPackagesToScan() {
return packagesToScan;
}
public void setPackagesToScan(String[] packagesToScan) {
this.packagesToScan = packagesToScan;
this.scanPackages(packagesToScan);
}
private boolean matchesFilter(MetadataReader reader, MetadataReaderFactory readerFactory) throws IOException {
for (TypeFilter filter : ENTITY_TYPE_FILTERS) {
if (filter.match(reader, readerFactory)) {
return true;
}
}
return false;
}
}

package com.meet58.base.servlet.mapping;

import java.io.IOException;

import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternUtils;
import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
import org.springframework.core.type.classreading.MetadataReader;
import org.springframework.core.type.classreading.MetadataReaderFactory;
import org.springframework.core.type.filter.AnnotationTypeFilter;
import org.springframework.core.type.filter.TypeFilter;
import org.springframework.util.ClassUtils;

import com.meet58.base.servlet.annotation.ServletHandler;

public class ServletHandlerMappingResolver {
	
	private static final String RESOURCE_PATTERN = "/**/*.class";
	
	private String[] packagesToScan;

	private ResourcePatternResolver resourcePatternResolver; 
	
	
	private static final TypeFilter[] ENTITY_TYPE_FILTERS = new TypeFilter[] {
		new AnnotationTypeFilter(ServletHandler.class, false)};

	
	public ServletHandlerMappingResolver(){
		this.resourcePatternResolver = ResourcePatternUtils.getResourcePatternResolver(new PathMatchingResourcePatternResolver());
	}
	
	public ServletHandlerMappingResolver scanPackages(String[] packagesToScan){
		try {
			for (String pkg : packagesToScan) {
				String pattern = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
						ClassUtils.convertClassNameToResourcePath(pkg) + RESOURCE_PATTERN;
				Resource[] resources;
				
					resources = this.resourcePatternResolver.getResources(pattern);
				
				MetadataReaderFactory readerFactory = new CachingMetadataReaderFactory(this.resourcePatternResolver);
				for (Resource resource : resources) {
					if (resource.isReadable()) {
						MetadataReader reader = readerFactory.getMetadataReader(resource);
						String className = reader.getClassMetadata().getClassName();
						if (matchesFilter(reader, readerFactory)) {
							ServletHandlerMappingFactory.addClassMapping(this.resourcePatternResolver.getClassLoader().loadClass(className));
						}
					}
				}
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return this;
	}
	
	public String[] getPackagesToScan() {
		return packagesToScan;
	}

	public void setPackagesToScan(String[] packagesToScan) {
		this.packagesToScan = packagesToScan;
		this.scanPackages(packagesToScan);
	}

	private boolean matchesFilter(MetadataReader reader, MetadataReaderFactory readerFactory) throws IOException {
		for (TypeFilter filter : ENTITY_TYPE_FILTERS) {
			if (filter.match(reader, readerFactory)) {
				return true;
			}
		}
		return false;
	}

}

這段代碼是Spring中如何掃描Hibernate持久化對象的代碼，拿過來借鑑了一下，下面要處理的就是把要處理的URL和相對應的ServletHandler進行匹配：

[java] view plain copy print ?

package com.meet58.base.servlet.mapping;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import org.apache.log4j.Logger;
import com.meet58.base.servlet.annotation.HandlerMapping;
import com.meet58.base.servlet.context.ServletHandlerFactory;
public class ServletHandlerMappingFactory {
private static Logger logger = Logger.getLogger(ServletHandlerMappingFactory.class);
private static Map<String, Method> servletHandlerMapping = new HashMap<String, Method>();
public static void addClassMapping(Class<?> clazz) {
String url = null;
HandlerMapping handlerMapping = clazz.getAnnotation(HandlerMapping.class);
if (handlerMapping != null) {
url = handlerMapping.value();
} else {
String classSimpleName = clazz.getSimpleName().toLowerCase();
url = "/" + classSimpleName.substring(0,
classSimpleName.indexOf("servlet"));
}
if (url != null) {
if(url.endsWith("/")){
url = url.substring(url.length() - 1);
}
ServletHandlerFactory.put(clazz);
logger.info(" Load servlet handler class:" + clazz.getName() + " url:" + url);
scanHandlerMethod(clazz,url);
}
}
public static void scanHandlerMethod(Class<?> clazz,String classMapping) {
Method[] methods = clazz.getDeclaredMethods();
for (Method method : methods) {
HandlerMapping handlerMapping = method.getAnnotation(HandlerMapping.class);
if (handlerMapping != null && handlerMapping.value() != null) {
String mapping = handlerMapping.value();
if(!mapping.startsWith("/")){
mapping = "/" + mapping;
}
mapping = classMapping + mapping;
addMethodMapping( mapping,method);
}
}
}
public static void addMethodMapping(String url,Method method) {
logger.info(" Load servlet handler mapping, method:" + method.getName() + " for url:" + url);
Method handlerMethod = servletHandlerMapping.get(url);
if(handlerMethod != null){
throw new IllegalArgumentException(" url :" + url + " is already mapped by :" + handlerMethod);
}else{
servletHandlerMapping.put(url, method);
}
}
public static Method getMethodMapping(String url) {
return servletHandlerMapping.get(url);
}
}

package com.meet58.base.servlet.mapping;

import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

import org.apache.log4j.Logger;

import com.meet58.base.servlet.annotation.HandlerMapping;
import com.meet58.base.servlet.context.ServletHandlerFactory;

public class ServletHandlerMappingFactory {
	
	private static Logger logger = Logger.getLogger(ServletHandlerMappingFactory.class);

	private static Map<String, Method> servletHandlerMapping = new HashMap<String, Method>();


	public static void addClassMapping(Class<?> clazz) {
		String url = null;
		HandlerMapping handlerMapping = clazz.getAnnotation(HandlerMapping.class);
		if (handlerMapping != null) {
			url = handlerMapping.value();
		} else {
			String classSimpleName = clazz.getSimpleName().toLowerCase();
			url = "/" + classSimpleName.substring(0,
							classSimpleName.indexOf("servlet"));
		}
		if (url != null) {
			if(url.endsWith("/")){
				url = url.substring(url.length() - 1);
			}
			ServletHandlerFactory.put(clazz);
			logger.info(" Load servlet handler class:" + clazz.getName() + " url:" + url);
			scanHandlerMethod(clazz,url);
		}
	}

	public static void scanHandlerMethod(Class<?> clazz,String classMapping) {
		Method[] methods = clazz.getDeclaredMethods();
		for (Method method : methods) {
			HandlerMapping handlerMapping = method.getAnnotation(HandlerMapping.class);
			if (handlerMapping != null && handlerMapping.value() != null) {
				String mapping = handlerMapping.value();
				if(!mapping.startsWith("/")){
					mapping = "/" + mapping;
				}
				mapping = classMapping + mapping;
				addMethodMapping( mapping,method);
			}
		}
	}

	public static void addMethodMapping(String url,Method method) {
		logger.info(" Load servlet handler mapping, method:" + method.getName() + " for url:" + url);
		Method handlerMethod = servletHandlerMapping.get(url);
		if(handlerMethod != null){
			throw new IllegalArgumentException(" url :" + url + " is already mapped by :" + handlerMethod);
		}else{
			servletHandlerMapping.put(url, method);
		}
	}

	public static Method getMethodMapping(String url) {
		return servletHandlerMapping.get(url);
	}
}

在這個類中掃描了每個ServletHandler類中的方法，並記錄他們的要處理的URL，接下來就是通過容器實例化這些ServletHandler類了：

[java] view plain copy print ?

package com.meet58.base.servlet.context;
import java.util.HashMap;
import java.util.Map;
import org.apache.log4j.Logger;
public class ServletHandlerFactory {
private static Logger logger = Logger.getLogger(ServletHandlerFactory.class);
private static Map<String,Object> classes = new HashMap<String,Object>();
public static void put(Class<?> clazz){
try {
logger.info("初始化ServletHandler類:"+ clazz.getName());
Object servlet = clazz.newInstance();
classes.put(clazz.getName(), servlet);
} catch (InstantiationException e) {
logger.error("初始化Servlet類:" + clazz.getName() + "失敗:" + e.getMessage());
} catch (IllegalAccessException e) {
logger.error("初始化Servlet類:" + clazz.getName() + "失敗:" + e.getMessage());
}
}
@SuppressWarnings("unchecked")
public static <T> T get(String className){
return (T)classes.get(className);
}
}

package com.meet58.base.servlet.context;

import java.util.HashMap;
import java.util.Map;

import org.apache.log4j.Logger;

public class ServletHandlerFactory {
	
	private static Logger logger = Logger.getLogger(ServletHandlerFactory.class);

	private static Map<String,Object> classes = new HashMap<String,Object>();
	
	public static void put(Class<?> clazz){
		try {
			logger.info("初始化ServletHandler類:"+ clazz.getName());
			Object servlet = clazz.newInstance();
			classes.put(clazz.getName(), servlet);
		} catch (InstantiationException e) {
			logger.error("初始化Servlet類:" + clazz.getName() + "失敗:" + e.getMessage());
		} catch (IllegalAccessException e) {
			logger.error("初始化Servlet類:" + clazz.getName() + "失敗:" + e.getMessage());
		}
	}
	
	@SuppressWarnings("unchecked")
	public static <T> T get(String className){
		return (T)classes.get(className);
	}
}

在ServletHandler類處理完成，並知道他們分別處理哪些URL之後，就可以通過一個調度器進行對對應的URL進行請求的分發了：

[java] view plain copy print ?

package com.meet58.base.servlet;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
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 org.apache.log4j.Logger;
import com.meet58.base.context.WebHttpRequestContext;
import com.meet58.base.servlet.context.ServletHandlerFactory;
import com.meet58.base.servlet.mapping.ServletHandlerMappingFactory;
import com.meet58.util.WebUtils;
@WebServlet(urlPatterns = { "*.do" })
public class WebHttpDispatchServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private Logger logger = Logger.getLogger(this.getClass());
private List<String> excludeUrls = new ArrayList<String>();
@Override
public void init() throws ServletException {
// 屏蔽websocket地址
excludeUrls.add("/meet.do");
super.init();
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
String url = request.getRequestURI().replace(
request.getContextPath(), "");
if (excludeUrls.contains(url)) {
return;
}
Method handlerMethod = ServletHandlerMappingFactory.getMethodMapping(url);
if (handlerMethod == null) {
response.sendError(404, "No handler found for " + url);
logger.error("No handler found for " + url);
return;
}
Object servlet = ServletHandlerFactory.get(handlerMethod
.getDeclaringClass().getName());
if (servlet == null) {
response.sendError(404, "No handler class found for " + url);
logger.error("No handler class found for " + url);
return;
}
Object result = invokeHandlerMethod(servlet, handlerMethod);
handleInvokeResult(result);
// this.doService();
} catch (Throwable e) {
handlerException(e);
}
}
public void handleInvokeResult(Object result) {
String location = "";
if (result instanceof String) {
if (((String) result).startsWith("redirect:")) {
location = ((String) result).substring("redirect:".length(),
((String) result).length());
WebUtils.redirect(location);
} else if (((String) result).startsWith("forward:")) {
location = ((String) result).substring("forward:".length(),
((String) result).length());
WebUtils.forward(location);
}
}
}
public Object invokeHandlerMethod(Object object, Method method)
throws Throwable {
Object result = null;
if (method != null) {
try {
result = method.invoke(object);
} catch (InvocationTargetException e) {
throw e.getTargetException();
}
}
return result;
}
public void handlerException(Throwable e) {
String message = e.getMessage() != null ? e.getMessage() : e.toString();
e.printStackTrace();
if (WebHttpRequestContext.isAsyncRequest()) {
WebUtils.writeFailure(message);
} else {
try {
WebHttpRequestContext.getResponse().sendError(500, message);
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
public String getMappingClass(String url) {
return null;
}
}

package com.meet58.base.servlet;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;

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 org.apache.log4j.Logger;

import com.meet58.base.context.WebHttpRequestContext;
import com.meet58.base.servlet.context.ServletHandlerFactory;
import com.meet58.base.servlet.mapping.ServletHandlerMappingFactory;
import com.meet58.util.WebUtils;

@WebServlet(urlPatterns = { "*.do" })
public class WebHttpDispatchServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	private Logger logger = Logger.getLogger(this.getClass());

	private List<String> excludeUrls = new ArrayList<String>();

	@Override
	public void init() throws ServletException {
		// 屏蔽websocket地址
		excludeUrls.add("/meet.do");
		super.init();
	}

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		this.doPost(request, response);
	}

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		try {
			String url = request.getRequestURI().replace(
					request.getContextPath(), "");
			if (excludeUrls.contains(url)) {
				return;
			}
			Method handlerMethod = ServletHandlerMappingFactory.getMethodMapping(url);
			if (handlerMethod == null) {
				response.sendError(404, "No handler found for " + url);
				logger.error("No handler found for " + url);
				return;
			}

			Object servlet = ServletHandlerFactory.get(handlerMethod
					.getDeclaringClass().getName());

			if (servlet == null) {
				response.sendError(404, "No handler class found for " + url);
				logger.error("No handler class found for " + url);
				return;
			}

			Object result = invokeHandlerMethod(servlet, handlerMethod);
			handleInvokeResult(result);

			// this.doService();
		} catch (Throwable e) {
			handlerException(e);
		}
	}

	public void handleInvokeResult(Object result) {
		String location = "";
		if (result instanceof String) {
			if (((String) result).startsWith("redirect:")) {
				location = ((String) result).substring("redirect:".length(),
						((String) result).length());
				WebUtils.redirect(location);
			} else if (((String) result).startsWith("forward:")) {
				location = ((String) result).substring("forward:".length(),
						((String) result).length());
				WebUtils.forward(location);
			}
		}
	}

	public Object invokeHandlerMethod(Object object, Method method)
			throws Throwable {
		Object result = null;
		if (method != null) {
			try {
				result = method.invoke(object);
			} catch (InvocationTargetException e) {
				throw e.getTargetException();
			}
		}
		return result;
	}

	public void handlerException(Throwable e) {
		String message = e.getMessage() != null ? e.getMessage() : e.toString();
		e.printStackTrace();
		if (WebHttpRequestContext.isAsyncRequest()) {
			WebUtils.writeFailure(message);
		} else {
			try {
				WebHttpRequestContext.getResponse().sendError(500, message);
			} catch (IOException e1) {
				e1.printStackTrace();
			}
		}
	}

	public String getMappingClass(String url) {
		return null;
	}

}

這段代碼中就是通過URL找到對應的處理方法來進行處理，並且捕獲異常。

這種方法Struts也是用到了，不過這個只是簡單的興趣研究並沒有在實際項目中運用，可能會存在線程安全的問題。

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