前言

流量转发一般是由ng还有网关来处理，但是在架构组工作里面，有些应用是不能接到业务网关，技术网关还在建设中，暂时实现服务进行流量转发

实现思路

可以重写servlet，然后通过httpclient来请求，然后复制对应response值、header、cookie来实现流量转发

上代码

第一步配置servlet

@Bean
    public ServletRegistrationBean servletRegistrationBean() {
        ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new MyProxyServlet(), "/proxy/*");
        //这个setName必须要设置，并且多个的时候，名字需要不一样
        servletRegistrationBean.setName("forward1");
        servletRegistrationBean.addInitParameter("targetUri", "xx.com");
        servletRegistrationBean.addInitParameter(ProxyServlet.P_LOG, "true");
        return servletRegistrationBean;
    }

就是/proxy的请求都会转发到xx.com这个域名

MyProxyServlet 继承HttpServlet




import cn.hutool.core.util.StrUtil;
import com.alibaba.fastjson.JSONObject;
import com.alibaba.fastjson.serializer.SerializerFeature;
import lombok.SneakyThrows;
import lombok.extern.slf4j.Slf4j;
import org.apache.commons.io.IOUtils;
import org.apache.http.*;
import org.apache.http.client.CookieStore;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.AbortableHttpRequest;
import org.apache.http.client.params.ClientPNames;
import org.apache.http.client.params.CookiePolicy;
import org.apache.http.client.utils.URIUtils;
import org.apache.http.conn.ssl.AllowAllHostnameVerifier;
import org.apache.http.conn.ssl.SSLContextBuilder;
import org.apache.http.entity.InputStreamEntity;
import org.apache.http.impl.client.BasicCookieStore;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicHeader;
import org.apache.http.message.BasicHttpEntityEnclosingRequest;
import org.apache.http.message.BasicHttpRequest;
import org.apache.http.message.HeaderGroup;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpParams;
import org.apache.http.util.EntityUtils;

import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.HttpCookie;
import java.net.URI;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.BitSet;
import java.util.Enumeration;
import java.util.Formatter;
import java.util.List;


@Slf4j
public class MyProxyServlet extends HttpServlet {

    /* INIT PARAMETER NAME CONSTANTS */

    /**
     * A boolean parameter name to enable logging of input and target URLs to the servlet log.
     */
    public static final String P_LOG = "log";

    /**
     * A boolean parameter name to enable forwarding of the client IP
     */
    public static final String P_FORWARDEDFOR = "forwardip";

    /**
     * The parameter name for the target (destination) URI to proxy to.
     */
    protected static final String P_TARGET_URI = "targetUri";
    protected static final String ATTR_TARGET_URI =
            org.mitre.dsmiley.httpproxy.ProxyServlet.class.getSimpleName() + ".targetUri";
    protected static final String ATTR_TARGET_HOST =
            org.mitre.dsmiley.httpproxy.ProxyServlet.class.getSimpleName() + ".targetHost";

    /* MISC */

    protected boolean doLog = false;
    protected boolean doForwardIP = true;
    /**
     * User agents shouldn't send the url fragment but what if it does?
     */
    protected boolean doSendUrlFragment = true;

    //These next 3 are cached here, and should only be referred to in initialization logic. See the
    // ATTR_* parameters.
    /**
     * From the configured parameter "targetUri".
     */
    protected String targetUri;
    protected URI targetUriObj;//new URI(targetUri)
    protected HttpHost targetHost;//URIUtils.extractHost(targetUriObj);

    private HttpClient proxyClient;

    @Override
    public String getServletInfo() {
        return "";
    }


    protected String getTargetUri(HttpServletRequest servletRequest) {
        return (String) servletRequest.getAttribute(ATTR_TARGET_URI);
    }

    private HttpHost getTargetHost(HttpServletRequest servletRequest) {
        return (HttpHost) servletRequest.getAttribute(ATTR_TARGET_HOST);
    }

    /**
     * Reads a configuration parameter. By default it reads servlet init parameters but
     * it can be overridden.
     */
    protected String getConfigParam(String key) {
        return getServletConfig().getInitParameter(key);
    }

    @Override
    public void init() throws ServletException {
        String doLogStr = getConfigParam(P_LOG);
        if (doLogStr != null) {
            this.doLog = Boolean.parseBoolean(doLogStr);
        }

        String doForwardIPString = getConfigParam(P_FORWARDEDFOR);
        if (doForwardIPString != null) {
            this.doForwardIP = Boolean.parseBoolean(doForwardIPString);
        }

        initTarget();//sets target*

        HttpParams hcParams = new BasicHttpParams();
        hcParams.setParameter(ClientPNames.COOKIE_POLICY, CookiePolicy.BROWSER_COMPATIBILITY);
        readConfigParam(hcParams, ClientPNames.HANDLE_REDIRECTS, Boolean.class);
        proxyClient = createHttpClient(hcParams);
    }

    protected void initTarget() throws ServletException {
        targetUri = getConfigParam(P_TARGET_URI);
        if (targetUri == null)
            throw new ServletException(P_TARGET_URI + " is required.");
        //test it's valid
        try {
            targetUriObj = new URI(targetUri);
        } catch (Exception e) {
            throw new ServletException("Trying to process targetUri init parameter: " + e, e);
        }
        targetHost = URIUtils.extractHost(targetUriObj);
    }

    private static CookieStore cookieStore = new BasicCookieStore();

    /**
     * Called from {@link #init(javax.servlet.ServletConfig)}. HttpClient offers many opportunities
     * for customization. By default,
     * <a href="http://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/impl/client/SystemDefaultHttpClient.html">
     * SystemDefaultHttpClient</a> is used if available, otherwise it falls
     * back to:
     * <pre>new DefaultHttpClient(new ThreadSafeClientConnManager(),hcParams)</pre>
     * SystemDefaultHttpClient uses PoolingClientConnectionManager. In any case, it should be thread-safe.
     */
    @SneakyThrows
    @SuppressWarnings({"unchecked", "deprecation"})
    protected HttpClient createHttpClient(HttpParams hcParams) {
        /*try {
            //as of HttpComponents v4.2, this class is better since it uses System
            // Properties:
            Class clientClazz = Class.forName("org.apache.http.impl.client.SystemDefaultHttpClient");
            Constructor constructor = clientClazz.getConstructor(HttpParams.class);
            return (HttpClient) constructor.newInstance(hcParams);
        } catch (ClassNotFoundException e) {
            //no problem; use v4.1 below
        } catch (Exception e) {
            throw new RuntimeException(e);
        }*/
        HttpClient httpClient = HttpClients.custom()
                .setDefaultCookieStore(cookieStore)
                .setHostnameVerifier(new AllowAllHostnameVerifier())
                .setSslcontext(new SSLContextBuilder().loadTrustMaterial(null, (chain, authType) -> true).build()).build();
        return httpClient;
        //Fallback on using older client:
        //return new DefaultHttpClient(new ThreadSafeClientConnManager(), hcParams);
    }

    /**
     * The http client used.
     *
     * @see #createHttpClient(HttpParams)
     */
    protected HttpClient getProxyClient() {
        return proxyClient;
    }

    /**
     * Reads a servlet config parameter by the name {@code hcParamName} of type {@code type}, and
     * set it in {@code hcParams}.
     */
    protected void readConfigParam(HttpParams hcParams, String hcParamName, Class type) {
        String val_str = getConfigParam(hcParamName);
        if (val_str == null)
            return;
        Object val_obj;
        if (type == String.class) {
            val_obj = val_str;
        } else {
            try {
                //noinspection unchecked
                val_obj = type.getMethod("valueOf", String.class).invoke(type, val_str);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
        hcParams.setParameter(hcParamName, val_obj);
    }

    @Override
    public void destroy() {
        //As of HttpComponents v4.3, clients implement closeable
        if (proxyClient instanceof Closeable) {//TODO AutoCloseable in Java 1.6
            try {
                ((Closeable) proxyClient).close();
            } catch (IOException e) {
                log("While destroying servlet, shutting down HttpClient: " + e, e);
            }
        } else {
            //Older releases require we do this:
            if (proxyClient != null)
                proxyClient.getConnectionManager().shutdown();
        }
        cookieStore = new BasicCookieStore();
        super.destroy();
    }

    @Override
    protected void service(HttpServletRequest servletRequest, HttpServletResponse servletResponse)
            throws ServletException, IOException {
        //initialize request attributes from caches if unset by a subclass by this point
        if (servletRequest.getAttribute(ATTR_TARGET_URI) == null) {
            servletRequest.setAttribute(ATTR_TARGET_URI, targetUri);
        }
        if (servletRequest.getAttribute(ATTR_TARGET_HOST) == null) {
            servletRequest.setAttribute(ATTR_TARGET_HOST, targetHost);
        }

        // Make the Request
        //note: we won't transfer the protocol version because I'm not sure it would truly be compatible
        String method = servletRequest.getMethod();
        String proxyRequestUri = rewriteUrlFromRequest(servletRequest);
        HttpRequest proxyRequest;
        //spec: RFC 2616, sec 4.3: either of these two headers signal that there is a message body.
        if (servletRequest.getHeader(HttpHeaders.CONTENT_LENGTH) != null ||
                servletRequest.getHeader(HttpHeaders.TRANSFER_ENCODING) != null) {
            HttpEntityEnclosingRequest eProxyRequest = new BasicHttpEntityEnclosingRequest(method, proxyRequestUri);
            // Add the input entity (streamed)
            //  note: we don't bother ensuring we close the servletInputStream since the container handles it
            eProxyRequest.setEntity(new InputStreamEntity(servletRequest.getInputStream(), servletRequest.getContentLength()));
            proxyRequest = eProxyRequest;
        } else
            proxyRequest = new BasicHttpRequest(method, proxyRequestUri);

        copyRequestHeaders(servletRequest, proxyRequest);

        setXForwardedForHeader(servletRequest, proxyRequest);

        HttpResponse proxyResponse = null;
        try {
            // Execute the request
            if (doLog) {
                log("proxy " + method + " uri: " + servletRequest.getRequestURI() + " -- " + proxyRequest.getRequestLine().getUri());
            }
            proxyResponse = proxyClient.execute(getTargetHost(servletRequest), proxyRequest);

            // Process the response
            int statusCode = proxyResponse.getStatusLine().getStatusCode();

            for (org.apache.http.cookie.Cookie cookie : cookieStore.getCookies()) {
                //set cookie name prefixed w/ a proxy value so it won't collide w/ other cookies
                String proxyCookieName = cookie.getName();
                Cookie servletCookie = new Cookie(proxyCookieName, cookie.getValue());
                servletCookie.setComment(cookie.getComment());
                servletCookie.setPath("/"); //set to the path of the proxy servlet
                // don't set cookie domain
                //servletCookie.setDomain("127.0.0.1");
                servletCookie.setSecure(false);
                servletCookie.setVersion(cookie.getVersion());
                servletResponse.addCookie(servletCookie);
            }

            // copying response headers to make sure SESSIONID or other Cookie which comes from remote server
            // will be saved in client when the proxied url was redirected to another one.
            // see issue [#51](https://github.com/mitre/HTTP-Proxy-Servlet/issues/51)
            copyResponseHeaders(proxyResponse, servletRequest, servletResponse);

            if (doResponseRedirectOrNotModifiedLogic(servletRequest, servletResponse, proxyResponse, statusCode)) {
                //the response is already "committed" now without any body to send
                return;
            }

            // Pass the response code. This method with the "reason phrase" is deprecated but it's the only way to pass the
            //  reason along too.
            //noinspection deprecation
            servletResponse.setStatus(statusCode, proxyResponse.getStatusLine().getReasonPhrase());

            // Send the content to the client
            copyResponseEntity(proxyResponse, servletResponse);
        } catch (Exception e) {
            //abort request, according to best practice with HttpClient
            if (proxyRequest instanceof AbortableHttpRequest) {
                AbortableHttpRequest abortableHttpRequest = (AbortableHttpRequest) proxyRequest;
                abortableHttpRequest.abort();
            }
            if (e instanceof RuntimeException)
                throw (RuntimeException) e;
            if (e instanceof ServletException)
                throw (ServletException) e;
            //noinspection ConstantConditions
            if (e instanceof IOException)
                throw (IOException) e;
            throw new RuntimeException(e);

        } finally {
            // make sure the entire entity was consumed, so the connection is released
            if (proxyResponse != null)
                consumeQuietly(proxyResponse.getEntity());
            cookieStore.clear();
            //Note: Don't need to close servlet outputStream:
            // http://stackoverflow.com/questions/1159168/should-one-call-close-on-httpservletresponse-getoutputstream-getwriter
        }
    }

    protected boolean doResponseRedirectOrNotModifiedLogic(
            HttpServletRequest servletRequest, HttpServletResponse servletResponse,
            HttpResponse proxyResponse, int statusCode)
            throws ServletException, IOException {
        // Check if the proxy response is a redirect
        // The following code is adapted from org.tigris.noodle.filters.CheckForRedirect
        if (statusCode >= HttpServletResponse.SC_MULTIPLE_CHOICES /* 300 */
                && statusCode < HttpServletResponse.SC_NOT_MODIFIED /* 304 */) {
            Header locationHeader = proxyResponse.getLastHeader(HttpHeaders.LOCATION);
            if (locationHeader == null) {
                throw new ServletException("Received status code: " + statusCode
                        + " but no " + HttpHeaders.LOCATION + " header was found in the response");
            }
            // Modify the redirect to go to this proxy servlet rather that the proxied host
            String locStr = rewriteUrlFromResponse(servletRequest, locationHeader.getValue());

            servletResponse.sendRedirect(locStr);
            return true;
        }
        // 304 needs special handling.  See:
        // http://www.ics.uci.edu/pub/ietf/http/rfc1945.html#Code304
        // We get a 304 whenever passed an 'If-Modified-Since'
        // header and the data on disk has not changed; server
        // responds w/ a 304 saying I'm not going to send the
        // body because the file has not changed.
        if (statusCode == HttpServletResponse.SC_NOT_MODIFIED) {
            servletResponse.setIntHeader(HttpHeaders.CONTENT_LENGTH, 0);
            servletResponse.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
            return true;
        }
        return false;
    }

    protected void closeQuietly(Closeable closeable) {
        try {
            closeable.close();
        } catch (IOException e) {
            log(e.getMessage(), e);
        }
    }

    /**
     * HttpClient v4.1 doesn't have the
     * {@link org.apache.http.util.EntityUtils#consumeQuietly(org.apache.http.HttpEntity)} method.
     */
    protected void consumeQuietly(HttpEntity entity) {
        try {
            EntityUtils.consume(entity);
        } catch (IOException e) {//ignore
            log(e.getMessage(), e);
        }
    }

    /**
     * These are the "hop-by-hop" headers that should not be copied.
     * http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
     * I use an HttpClient HeaderGroup class instead of Set<String> because this
     * approach does case insensitive lookup faster.
     */
    protected static final HeaderGroup hopByHopHeaders;

    static {
        hopByHopHeaders = new HeaderGroup();
        String[] headers = new String[]{
                "Connection", "Keep-Alive", "Proxy-Authenticate", "Proxy-Authorization",
                "TE", "Trailers", "Transfer-Encoding", "Upgrade"};
        for (String header : headers) {
            hopByHopHeaders.addHeader(new BasicHeader(header, null));
        }
    }

    /**
     * Copy request headers from the servlet client to the proxy request.
     */
    protected void copyRequestHeaders(HttpServletRequest servletRequest, HttpRequest proxyRequest) {
        // Get an Enumeration of all of the header names sent by the client
        Enumeration enumerationOfHeaderNames = servletRequest.getHeaderNames();
        while (enumerationOfHeaderNames.hasMoreElements()) {
            String headerName = (String) enumerationOfHeaderNames.nextElement();
            //Instead the content-length is effectively set via InputStreamEntity
            if (headerName.equalsIgnoreCase(HttpHeaders.CONTENT_LENGTH))
                continue;
            if (hopByHopHeaders.containsHeader(headerName))
                continue;

            Enumeration headers = servletRequest.getHeaders(headerName);
            while (headers.hasMoreElements()) {//sometimes more than one value
                String headerValue = (String) headers.nextElement();
                // In case the proxy host is running multiple virtual servers,
                // rewrite the Host header to ensure that we get content from
                // the correct virtual server
                if (headerName.equalsIgnoreCase(HttpHeaders.HOST)) {
                    HttpHost host = getTargetHost(servletRequest);
                    headerValue = host.getHostName();
                    if (host.getPort() != -1)
                        headerValue += ":" + host.getPort();
                } else if (headerName.equalsIgnoreCase(org.apache.http.cookie.SM.COOKIE)) {
                    headerValue = getRealCookie(headerValue);
                }
                proxyRequest.addHeader(headerName, headerValue);
            }
        }
    }

    private void setXForwardedForHeader(HttpServletRequest servletRequest,
                                        HttpRequest proxyRequest) {
        String headerName = "X-Forwarded-For";
        if (doForwardIP) {
            String newHeader = servletRequest.getRemoteAddr();
            String existingHeader = servletRequest.getHeader(headerName);
            if (existingHeader != null) {
                newHeader = existingHeader + ", " + newHeader;
            }
            proxyRequest.setHeader(headerName, newHeader);
        }
    }

    /**
     * Copy proxied response headers back to the servlet client.
     */
    protected void copyResponseHeaders(HttpResponse proxyResponse, HttpServletRequest servletRequest,
                                       HttpServletResponse servletResponse) {
        for (Header header : proxyResponse.getAllHeaders()) {
            if (hopByHopHeaders.containsHeader(header.getName()))
                continue;
            if (header.getName().equalsIgnoreCase(org.apache.http.cookie.SM.SET_COOKIE) ||
                    header.getName().equalsIgnoreCase(org.apache.http.cookie.SM.SET_COOKIE2)) {
                copyProxyCookie(servletRequest, servletResponse, header);
            } else {
                servletResponse.addHeader(header.getName(), header.getValue());
            }
        }
    }

    /**
     * Copy cookie from the proxy to the servlet client.
     * Replaces cookie path to local path and renames cookie to avoid collisions.
     */
    protected void copyProxyCookie(HttpServletRequest servletRequest,
                                   HttpServletResponse servletResponse, Header header) {
        List<HttpCookie> cookies = HttpCookie.parse(header.getValue());
        String path = servletRequest.getContextPath(); // path starts with / or is empty string
        path += servletRequest.getServletPath(); // servlet path starts with / or is empty string

        for (HttpCookie cookie : cookies) {
            //set cookie name prefixed w/ a proxy value so it won't collide w/ other cookies
            String proxyCookieName = cookie.getName();
            Cookie servletCookie = new Cookie(proxyCookieName, cookie.getValue());
            servletCookie.setComment(cookie.getComment());
            servletCookie.setMaxAge((int) cookie.getMaxAge());
            servletCookie.setPath(path); //set to the path of the proxy servlet
            // don't set cookie domain
            servletCookie.setSecure(cookie.getSecure());
            servletCookie.setVersion(cookie.getVersion());
            servletResponse.addCookie(servletCookie);
        }
    }

    /**
     * Take any client cookies that were originally from the proxy and prepare them to send to the
     * proxy.  This relies on cookie headers being set correctly according to RFC 6265 Sec 5.4.
     * This also blocks any local cookies from being sent to the proxy.
     */
    protected String getRealCookie(String cookieValue) {
        StringBuilder escapedCookie = new StringBuilder();
        String cookies[] = cookieValue.split("; ");
        for (String cookie : cookies) {
            String cookieSplit[] = cookie.split("=");
            if (cookieSplit.length == 2) {
                String cookieName = cookieSplit[0];
                if (cookieName.startsWith(getCookieNamePrefix())) {
                    cookieName = cookieName.substring(getCookieNamePrefix().length());
                    if (escapedCookie.length() > 0) {
                        escapedCookie.append("; ");
                    }
                    escapedCookie.append(cookieName).append("=").append(cookieSplit[1]);
                }
            }

            cookieValue = escapedCookie.toString();
        }
        return cookieValue;
    }

    /**
     * The string prefixing rewritten cookies.
     */
    protected String getCookieNamePrefix() {
        return getServletConfig().getServletName();
    }

    /**
     * Copy response body data (the entity) from the proxy to the servlet client.
     */
    protected void copyResponseEntity(HttpResponse proxyResponse, HttpServletResponse servletResponse) throws IOException {
        HttpEntity entity = proxyResponse.getEntity();
        if (entity != null) {
            OutputStream servletOutputStream = servletResponse.getOutputStream();
            entity.writeTo(servletOutputStream);
        }
    }

    /**
     * Reads the request URI from {@code servletRequest} and rewrites it, considering targetUri.
     * It's used to make the new request.
     */
    protected String rewriteUrlFromRequest(HttpServletRequest servletRequest) {
        StringBuilder uri = new StringBuilder(500);
        uri.append(getTargetUri(servletRequest));
        // Handle the path given to the servlet
        if (servletRequest.getPathInfo() != null) {//ex: /my/path.html
            uri.append(encodeUriQuery(servletRequest.getPathInfo()));
        }
        // Handle the query string & fragment
        String queryString = servletRequest.getQueryString();//ex:(following '?'): name=value&foo=bar#fragment
        String fragment = null;
        //split off fragment from queryString, updating queryString if found
        if (queryString != null) {
            int fragIdx = queryString.indexOf('#');
            if (fragIdx >= 0) {
                fragment = queryString.substring(fragIdx + 1);
                queryString = queryString.substring(0, fragIdx);
            }
        }

        queryString = rewriteQueryStringFromRequest(servletRequest, queryString);
        if (queryString != null && queryString.length() > 0) {
            uri.append('?');
            uri.append(encodeUriQuery(queryString));
        }

        if (doSendUrlFragment && fragment != null) {
            uri.append('#');
            uri.append(encodeUriQuery(fragment));
        }
        return uri.toString();
    }

    protected String rewriteQueryStringFromRequest(HttpServletRequest servletRequest, String queryString) {
        return queryString;
    }

    /**
     * For a redirect response from the target server, this translates {@code theUrl} to redirect to
     * and translates it to one the original client can use.
     */
    protected String rewriteUrlFromResponse(HttpServletRequest servletRequest, String theUrl) {
        //TODO document example paths
        final String targetUri = getTargetUri(servletRequest);
        if (theUrl.startsWith(targetUri)) {
            String curUrl = servletRequest.getRequestURL().toString();//no query
            String pathInfo = servletRequest.getPathInfo();
            if (pathInfo != null) {
                assert curUrl.endsWith(pathInfo);
                curUrl = curUrl.substring(0, curUrl.length() - pathInfo.length());//take pathInfo off
            }
            theUrl = curUrl + theUrl.substring(targetUri.length());
        }
        return theUrl;
    }

    /**
     * The target URI as configured. Not null.
     */
    public String getTargetUri() {
        return targetUri;
    }

    /**
     * Encodes characters in the query or fragment part of the URI.
     *
     * <p>Unfortunately, an incoming URI sometimes has characters disallowed by the spec.  HttpClient
     * insists that the outgoing proxied request has a valid URI because it uses Java's {@link URI}.
     * To be more forgiving, we must escape the problematic characters.  See the URI class for the
     * spec.
     *
     * @param in example: name=value&foo=bar#fragment
     */
    protected static CharSequence encodeUriQuery(CharSequence in) {
        //Note that I can't simply use URI.java to encode because it will escape pre-existing escaped things.
        StringBuilder outBuf = null;
        Formatter formatter = null;
        for (int i = 0; i < in.length(); i++) {
            char c = in.charAt(i);
            boolean escape = true;
            if (c < 128) {
                if (asciiQueryChars.get((int) c)) {
                    escape = false;
                }
            } else if (!Character.isISOControl(c) && !Character.isSpaceChar(c)) {//not-ascii
                escape = false;
            }
            if (!escape) {
                if (outBuf != null)
                    outBuf.append(c);
            } else {
                //escape
                if (outBuf == null) {
                    outBuf = new StringBuilder(in.length() + 5 * 3);
                    outBuf.append(in, 0, i);
                    formatter = new Formatter(outBuf);
                }
                //leading %, 0 padded, width 2, capital hex
                formatter.format("%%%02X", (int) c);//TODO
            }
        }
        return outBuf != null ? outBuf : in;
    }

    protected static final BitSet asciiQueryChars;

    static {
        char[] c_unreserved = "_-!.~'()*".toCharArray();//plus alphanum
        char[] c_punct = ",;:$&+=".toCharArray();
        char[] c_reserved = "?/[]@".toCharArray();//plus punct

        asciiQueryChars = new BitSet(128);
        for (char c = 'a'; c <= 'z'; c++) asciiQueryChars.set((int) c);
        for (char c = 'A'; c <= 'Z'; c++) asciiQueryChars.set((int) c);
        for (char c = '0'; c <= '9'; c++) asciiQueryChars.set((int) c);
        for (char c : c_unreserved) asciiQueryChars.set((int) c);
        for (char c : c_punct) asciiQueryChars.set((int) c);
        for (char c : c_reserved) asciiQueryChars.set((int) c);

        asciiQueryChars.set((int) '%');//leave existing percent escapes in place
    }

}