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# Valves and Pipeline
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Request processing pipeline using chain-of-responsibility pattern with valves for cross-cutting concerns including access logging, authentication, error handling, compression, URL rewriting, remote address filtering, and custom request/response processing.
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## Capabilities
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### Valve Interface
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Base interface for all valves in the processing pipeline.
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```java { .api }
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public interface Valve {
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    // Next valve in chain
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    Valve getNext();
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    void setNext(Valve valve);
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    // Processing
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    void invoke(Request request, Response response) throws IOException, ServletException;
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    boolean isAsyncSupported();
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    // Background processing
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    void backgroundProcess();
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}
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```
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### Pipeline Interface
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Container for managing valve chains.
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```java { .api }
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public interface Pipeline extends Contained {
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    // Basic valve (end of chain)
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    Valve getBasic();
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    void setBasic(Valve valve);
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    // Valve management
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    void addValve(Valve valve);
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    Valve[] getValves();
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    void removeValve(Valve valve);
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    Valve getFirst();
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    // Async support
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    boolean isAsyncSupported();
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    void findNonAsyncValves(Set<String> result);
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}
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```
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### Common Valve Types
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Standard valves provided by Tomcat.
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```java { .api }
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// Access logging valve
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public class AccessLogValve extends ValveBase implements AccessLog {
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    // Log pattern configuration
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    public void setPattern(String pattern);
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    public String getPattern();
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    // File configuration
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    public void setDirectory(String directory);
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    public String getDirectory();
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    public void setPrefix(String prefix);
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    public String getPrefix();
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    public void setSuffix(String suffix);
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    public String getSuffix();
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    // Rotation
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    public void setRotatable(boolean rotatable);
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    public boolean isRotatable();
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    public void setFileDateFormat(String fileDateFormat);
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    public String getFileDateFormat();
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    // Buffering
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    public void setBuffered(boolean buffered);
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    public boolean isBuffered();
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    // Request attributes
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    public void setRequestAttributesEnabled(boolean requestAttributesEnabled);
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    public boolean getRequestAttributesEnabled();
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException;
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    public void log(Request request, Response response, long time);
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}
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// Error report valve
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public class ErrorReportValve extends ValveBase {
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    public void setShowReport(boolean showReport);
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    public boolean isShowReport();
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    public void setShowServerInfo(boolean showServerInfo);
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    public boolean isShowServerInfo();
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException;
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}
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// Remote address filter valve
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public class RemoteAddrValve extends RequestFilterValve {
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException;
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}
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// Remote host filter valve
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public class RemoteHostValve extends RequestFilterValve {
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException;
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}
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// Remote IP valve (X-Forwarded-For handling)
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public class RemoteIpValve extends ValveBase {
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    public void setRemoteIpHeader(String header);
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    public void setProxiesHeader(String header);
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    public void setTrustedProxies(String trustedProxies);
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException;
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}
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// SSL valve (SSL termination support)
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public class SSLValve extends ValveBase {
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    public void setSslCipherHeader(String header);
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    public void setSslSessionIdHeader(String header);
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    public void setSslClientCertHeader(String header);
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException;
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}
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// Stuck thread detection valve
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public class StuckThreadDetectionValve extends ValveBase {
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    public void setThreshold(int threshold);
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    public void setInterruptThreadThreshold(int interruptThreadThreshold);
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException;
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}
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```
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## Usage Examples
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### Adding Custom Valve
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```java
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import org.apache.catalina.connector.Request;
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import org.apache.catalina.connector.Response;
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import org.apache.catalina.valves.ValveBase;
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import org.apache.catalina.startup.Tomcat;
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import org.apache.catalina.Context;
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import jakarta.servlet.ServletException;
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import java.io.IOException;
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public class CustomValveExample extends ValveBase {
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    @Override
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    public void invoke(Request request, Response response) throws IOException, ServletException {
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        // Pre-processing
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        long startTime = System.currentTimeMillis();
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        System.out.println("Request: " + request.getRequestURI());
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        // Continue chain
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        getNext().invoke(request, response);
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        // Post-processing
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        long duration = System.currentTimeMillis() - startTime;
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        System.out.println("Completed in " + duration + "ms");
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    }
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    public static void main(String[] args) throws Exception {
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        Tomcat tomcat = new Tomcat();
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        tomcat.setPort(8080);
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        Context ctx = tomcat.addContext("", System.getProperty("java.io.tmpdir"));
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        // Add custom valve
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        ctx.getPipeline().addValve(new CustomValveExample());
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        tomcat.start();
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        tomcat.getServer().await();
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    }
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}
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```
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