Tomcat实现动态context切换

需求:

希望通过request header来动态请求不同的war包(即Context)

问题:

由于servlet只提供了filter进行过滤,而filter实现在context中,所以该需求以servlet标准无法实现.

解决方法:

Tomcat在context以上存在engine和host层.因此在host层加入一层valve过滤,通过判断request header,重写request URI, context和wrapper(servlet)来动态实现context的切换.

代码实现:

Valve类:

package com.mobiscloud;

import java.io.IOException;

import javax.servlet.ServletException;

import org.apache.catalina.Context;
import org.apache.catalina.Host;
import org.apache.catalina.Wrapper;
import org.apache.catalina.connector.Request;
import org.apache.catalina.connector.Response;
import org.apache.catalina.valves.ValveBase;
import org.apache.tomcat.util.buf.MessageBytes;

public class ProxyValve extends ValveBase {
//	private static String QUESTION_MARK ="?";

	@Override
	public void invoke(Request request, Response response) throws IOException,
			ServletException {
		String currentContext = "/miaomiao";
		String currentContextName = "miaomiao";
		String nextContext = "/cloudcrawlweb";
		String nextContextName = "cloudcrawlweb";
		
		String decodedRequestURI = request.getDecodedRequestURI();
		// Judge context
		if (decodedRequestURI.contains(currentContext)) {
			// Replace current context to new context
			org.apache.coyote.Request coyoteRequest = request.getCoyoteRequest();
			String newPathStr = coyoteRequest.decodedURI().getString().replace(currentContextName, nextContextName); // Don't have query string

			MessageBytes contextPath = MessageBytes.newInstance();
			contextPath.setString(nextContext);
			request.getMappingData().contextPath = contextPath;
			
			// Rewrite request URI
			MessageBytes newPath = MessageBytes.newInstance();
			newPath.setString(newPathStr);
	        coyoteRequest.requestURI().duplicate(newPath);
	        coyoteRequest.decodedURI().duplicate(newPath);
	        coyoteRequest.getURLDecoder().convert(newPath, false);
	        coyoteRequest.unparsedURI().duplicate(newPath);
			
			// Get request suffix URI
			MessageBytes path = MessageBytes.newInstance();
			path.setString(newPathStr.substring(nextContext.length()));
			request.getMappingData().requestPath = path;
			request.getMappingData().wrapperPath = path;

			// Get Context
			Host host = request.getHost();
			Context context = (Context)host.findChild(nextContext);
			request.getMappingData().context = context;
            request.setContext(context);
            
            // Get wrapper
            String wrapperName = context.findServletMapping(path.getString());
            request.setWrapper((Wrapper) context.findChild(wrapperName));
            
            // Get next valve
			getNext().invoke(request, response);
		} else {
			getNext().invoke(request, response);
		}
	}
}

Server.xml

<?xml version="1.0" encoding="UTF-8"?>
<Server port="8005" shutdown="SHUTDOWN">
...
	<Service name="Catalina">
	...
		<Engine defaultHost="localhost" name="Catalina">
			...
			<Host appBase="webapps" autoDeploy="true" name="localhost"
						unpackWARs="true">
						...
						<Valve className="com.mobiscloud.ProxyValve" />
			</Host>
		</Engine>
	</Service>
</Server>

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