Refactor String#replaceAll (#3199)

If we repeatedly call String#replaceAll, we internally repeatedly call the regular expression pattern compilation every time as following:

```java
    public String replaceAll(String regex, String replacement) {
        return Pattern.compile(regex).matcher(this).replaceAll(replacement);
    }
```
The modifications are to keep the compiled pattern.
Therefore, compiling a relatively expensive regular expression pattern does not have to be done every time.

spring-cloud-netflix-zuul/src/main/java/org/springframework/cloud/netflix/zuul/filters/ProxyRequestHelper.java

@@ -27,6 +27,7 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.regex.Pattern;
 import java.util.Set;
 
 import javax.servlet.http.HttpServletRequest;
@@ -63,6 +64,10 @@ public class ProxyRequestHelper {
 	 */
 	public static final String IGNORED_HEADERS = "ignoredHeaders";
 
+	public static final Pattern FORM_FEED_PATTERN = Pattern.compile("\f");
+
+	public static final Pattern COLON_PATTERN = Pattern.compile(":");
+
 	private Set<String> ignoredHeaders = new LinkedHashSet<>();
 
 	private Set<String> sensitiveHeaders = new LinkedHashSet<>();
@@ -283,11 +288,11 @@ public class ProxyRequestHelper {
 					// if form feed is already part of param name double
 					// since form feed is used as the colon replacement below
 					if (key.contains("\f")) {
-						key = (key.replaceAll("\f", "\f\f"));
+						key = (FORM_FEED_PATTERN.matcher(key).replaceAll("\f\f"));
 					}
 					// colon is special to UriTemplate
 					if (key.contains(":")) {
-						key = key.replaceAll(":", "\f");
+						key = COLON_PATTERN.matcher(key).replaceAll("\f");
 					}
 					key = key + i;
 					singles.put(key, value);

spring-cloud-netflix-zuul/src/main/java/org/springframework/cloud/netflix/zuul/filters/discovery/PatternServiceRouteMapper.java

@@ -21,6 +21,8 @@ import org.springframework.util.StringUtils;
  */
 public class PatternServiceRouteMapper implements ServiceRouteMapper {
 
+	private static final Pattern MULTIPLE_SLASH_PATTERN = Pattern.compile("/{2,}");
+
 	/**
 	 * A RegExp Pattern that extract needed information from a service ID. Ex :
 	 * "(?<name>.*)-(?<version>v.*$)"
@@ -60,7 +62,7 @@ public class PatternServiceRouteMapper implements ServiceRouteMapper {
 	 * @return
 	 */
 	private String cleanRoute(final String route) {
-		String routeToClean = route.replaceAll("/{2,}", "/");
+		String routeToClean = MULTIPLE_SLASH_PATTERN.matcher(route).replaceAll("/");
 		if (routeToClean.startsWith("/")) {
 			routeToClean = routeToClean.substring(1);
 		}

spring-cloud-netflix-zuul/src/main/java/org/springframework/cloud/netflix/zuul/filters/pre/PreDecorationFilter.java

@@ -18,6 +18,7 @@ package org.springframework.cloud.netflix.zuul.filters.pre;
 
 import java.net.MalformedURLException;
 import java.net.URL;
+import java.util.regex.Pattern;
 
 import javax.servlet.http.HttpServletRequest;
 
@@ -70,6 +71,8 @@ public class PreDecorationFilter extends ZuulFilter {
 	@Deprecated
 	public static final int FILTER_ORDER = PRE_DECORATION_FILTER_ORDER;
 
+	public static final Pattern DOUBLE_SLASH = Pattern.compile("//");
+
 	private RouteLocator routeLocator;
 
 	private String dispatcherServletPath;
@@ -185,7 +188,7 @@ public class PreDecorationFilter extends ZuulFilter {
 				fallBackUri = "/" + fallBackUri;
 			}
 			String forwardURI = fallbackPrefix + fallBackUri;
-			forwardURI = forwardURI.replaceAll("//", "/");
+			forwardURI = DOUBLE_SLASH.matcher(forwardURI).replaceAll("/");
 			ctx.set(FORWARD_TO_KEY, forwardURI);
 		}
 		return null;

spring-cloud-netflix-zuul/src/main/java/org/springframework/cloud/netflix/zuul/filters/route/SimpleHostRoutingFilter.java

@@ -22,6 +22,7 @@ import java.net.URL;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
+import java.util.regex.Pattern;
 import java.util.Timer;
 import java.util.TimerTask;
 
@@ -85,6 +86,8 @@ public class SimpleHostRoutingFilter extends ZuulFilter {
 
 	private static final Log log = LogFactory.getLog(SimpleHostRoutingFilter.class);
 
+	private static final Pattern MULTIPLE_SLASH_PATTERN = Pattern.compile("/{2,}");
+
 	private final Timer connectionManagerTimer = new Timer(
 			"SimpleHostRoutingFilter.connectionManagerTimer", true);
 
@@ -286,7 +289,7 @@ public class SimpleHostRoutingFilter extends ZuulFilter {
 				requestEntity);
 		URL host = RequestContext.getCurrentContext().getRouteHost();
 		HttpHost httpHost = getHttpHost(host);
-		uri = StringUtils.cleanPath((host.getPath() + uri).replaceAll("/{2,}", "/"));
+		uri = StringUtils.cleanPath(MULTIPLE_SLASH_PATTERN.matcher(host.getPath() + uri).replaceAll("/"));
 		long contentLength = getContentLength(request);
 
 		ContentType contentType = null;
@@ -449,4 +452,4 @@ public class SimpleHostRoutingFilter extends ZuulFilter {
 		}
 		return request.getContentLength();
 	}
-}
+}