tomcat的servlet读取请求参数

读取url上的queryString

org/apache/tomcat/embed/tomcat-embed-core/8.0.33/tomcat-embed-core-8.0.33-sources.jar!/org/apache/catalina/core/ApplicationDispatcher.java

private void doDispatch(ServletRequest request, ServletResponse response) throws ServletException, IOException 
private void doForward(ServletRequest request, ServletResponse response)
        throws ServletException, IOException
private void doInclude(ServletRequest request, ServletResponse response)
            throws ServletException, IOException

这里看doDispatch

private void doDispatch(ServletRequest request, ServletResponse response)
            throws ServletException, IOException {

        // Set up to handle the specified request and response
        State state = new State(request, response, false);

        // Create a wrapped response to use for this request
        wrapResponse(state);

        ApplicationHttpRequest wrequest =
            (ApplicationHttpRequest) wrapRequest(state);

        if (queryString != null) {
            wrequest.setQueryParams(queryString);
        }

        wrequest.setAttribute(Globals.DISPATCHER_TYPE_ATTR,
                DispatcherType.ASYNC);
        wrequest.setAttribute(Globals.DISPATCHER_REQUEST_PATH_ATTR,
                getCombinedPath());

        wrequest.setContextPath(context.getPath());
        wrequest.setRequestURI(requestURI);
        wrequest.setServletPath(servletPath);
        wrequest.setPathInfo(pathInfo);
        if (queryString != null) {
            wrequest.setQueryString(queryString);
            wrequest.setQueryParams(queryString);
        }

        invoke(state.outerRequest, state.outerResponse, state);
    }

ApplicationDispatcher.doDispatch-->ApplicationHttpRequest.setQueryString -->ApplicationHttpRequest.parseParameters -->mergeParameters

private void mergeParameters() {

        if ((queryParamString == null) || (queryParamString.length() < 1))
            return;

        // Parse the query string from the dispatch target
        Parameters paramParser = new Parameters();
        MessageBytes queryMB = MessageBytes.newInstance();
        queryMB.setString(queryParamString);

        String encoding = getCharacterEncoding();
        // No need to process null value, as ISO-8859-1 is the default encoding
        // in MessageBytes.toBytes().
        if (encoding != null) {
            try {
                queryMB.setCharset(B2CConverter.getCharset(encoding));
            } catch (UnsupportedEncodingException ignored) {
                // Fall-back to ISO-8859-1
            }
        }

        paramParser.setQuery(queryMB);
        paramParser.setQueryStringEncoding(encoding);
        paramParser.handleQueryParameters();

        // Insert the additional parameters from the dispatch target
        Enumeration<String> dispParamNames = paramParser.getParameterNames();
        while (dispParamNames.hasMoreElements()) {
            String dispParamName = dispParamNames.nextElement();
            String[] dispParamValues = paramParser.getParameterValues(dispParamName);
            String[] originalValues = parameters.get(dispParamName);
            if (originalValues == null) {
                parameters.put(dispParamName, dispParamValues);
                continue;
            }
            parameters.put(dispParamName, mergeValues(dispParamValues, originalValues));
        }
    }

读取post及body的参数

org/apache/tomcat/embed/tomcat-embed-core/8.0.33/tomcat-embed-core-8.0.33-sources.jar!/org/apache/catalina/connector/Request.java

/**
     * Parse request parameters.
     */
    protected void parseParameters() {

        parametersParsed = true;

        Parameters parameters = coyoteRequest.getParameters();
        boolean success = false;
        try {
            // Set this every time in case limit has been changed via JMX
            parameters.setLimit(getConnector().getMaxParameterCount());

            // getCharacterEncoding() may have been overridden to search for
            // hidden form field containing request encoding
            String enc = getCharacterEncoding();

            boolean useBodyEncodingForURI = connector.getUseBodyEncodingForURI();
            if (enc != null) {
                parameters.setEncoding(enc);
                if (useBodyEncodingForURI) {
                    parameters.setQueryStringEncoding(enc);
                }
            } else {
                parameters.setEncoding
                    (org.apache.coyote.Constants.DEFAULT_CHARACTER_ENCODING);
                if (useBodyEncodingForURI) {
                    parameters.setQueryStringEncoding
                        (org.apache.coyote.Constants.DEFAULT_CHARACTER_ENCODING);
                }
            }

            parameters.handleQueryParameters();

            if (usingInputStream || usingReader) {
                success = true;
                return;
            }

            if( !getConnector().isParseBodyMethod(getMethod()) ) {
                success = true;
                return;
            }

            String contentType = getContentType();
            if (contentType == null) {
                contentType = "";
            }
            int semicolon = contentType.indexOf(';');
            if (semicolon >= 0) {
                contentType = contentType.substring(0, semicolon).trim();
            } else {
                contentType = contentType.trim();
            }

            if ("multipart/form-data".equals(contentType)) {
                parseParts(false);
                success = true;
                return;
            }

            if (!("application/x-www-form-urlencoded".equals(contentType))) {
                success = true;
                return;
            }

            int len = getContentLength();

            if (len > 0) {
                int maxPostSize = connector.getMaxPostSize();
                if ((maxPostSize >= 0) && (len > maxPostSize)) {
                    Context context = getContext();
                    if (context != null && context.getLogger().isDebugEnabled()) {
                        context.getLogger().debug(
                                sm.getString("coyoteRequest.postTooLarge"));
                    }
                    checkSwallowInput();
                    parameters.setParseFailedReason(FailReason.POST_TOO_LARGE);
                    return;
                }
                byte[] formData = null;
                if (len < CACHED_POST_LEN) {
                    if (postData == null) {
                        postData = new byte[CACHED_POST_LEN];
                    }
                    formData = postData;
                } else {
                    formData = new byte[len];
                }
                try {
                    if (readPostBody(formData, len) != len) {
                        parameters.setParseFailedReason(FailReason.REQUEST_BODY_INCOMPLETE);
                        return;
                    }
                } catch (IOException e) {
                    // Client disconnect
                    Context context = getContext();
                    if (context != null && context.getLogger().isDebugEnabled()) {
                        context.getLogger().debug(
                                sm.getString("coyoteRequest.parseParameters"),
                                e);
                    }
                    parameters.setParseFailedReason(FailReason.CLIENT_DISCONNECT);
                    return;
                }
                parameters.processParameters(formData, 0, len);
            } else if ("chunked".equalsIgnoreCase(
                    coyoteRequest.getHeader("transfer-encoding"))) {
                byte[] formData = null;
                try {
                    formData = readChunkedPostBody();
                } catch (IllegalStateException ise) {
                    // chunkedPostTooLarge error
                    parameters.setParseFailedReason(FailReason.POST_TOO_LARGE);
                    Context context = getContext();
                    if (context != null && context.getLogger().isDebugEnabled()) {
                        context.getLogger().debug(
                                sm.getString("coyoteRequest.parseParameters"),
                                ise);
                    }
                    return;
                } catch (IOException e) {
                    // Client disconnect
                    parameters.setParseFailedReason(FailReason.CLIENT_DISCONNECT);
                    Context context = getContext();
                    if (context != null && context.getLogger().isDebugEnabled()) {
                        context.getLogger().debug(
                                sm.getString("coyoteRequest.parseParameters"),
                                e);
                    }
                    return;
                }
                if (formData != null) {
                    parameters.processParameters(formData, 0, formData.length);
                }
            }
            success = true;
        } finally {
            if (!success) {
                parameters.setParseFailedReason(FailReason.UNKNOWN);
            }
        }

    }

readPostBody

/**
     * Read post body in an array.
     */
    protected int readPostBody(byte body[], int len)
        throws IOException {

        int offset = 0;
        do {
            int inputLen = getStream().read(body, offset, len - offset);
            if (inputLen <= 0) {
                return offset;
            }
            offset += inputLen;
        } while ((len - offset) > 0);
        return len;

    }

readChunkedPostBody

/**
     * Read chunked post body.
     */
    protected byte[] readChunkedPostBody() throws IOException {
        ByteChunk body = new ByteChunk();

        byte[] buffer = new byte[CACHED_POST_LEN];

        int len = 0;
        while (len > -1) {
            len = getStream().read(buffer, 0, CACHED_POST_LEN);
            if (connector.getMaxPostSize() >= 0 &&
                    (body.getLength() + len) > connector.getMaxPostSize()) {
                // Too much data
                checkSwallowInput();
                throw new IllegalStateException(
                        sm.getString("coyoteRequest.chunkedPostTooLarge"));
            }
            if (len > 0) {
                body.append(buffer, 0, len);
            }
        }
        if (body.getLength() == 0) {
            return null;
        }
        if (body.getLength() < body.getBuffer().length) {
            int length = body.getLength();
            byte[] result = new byte[length];
            System.arraycopy(body.getBuffer(), 0, result, 0, length);
            return result;
        }

        return body.getBuffer();
    }

parameters.processParameters(formData, 0, formData.length);

-->addParameter

public void addParameter( String key, String value )
            throws IllegalStateException {

        if( key==null ) {
            return;
        }

        parameterCount ++;
        if (limit > -1 && parameterCount > limit) {
            // Processing this parameter will push us over the limit. ISE is
            // what Request.parseParts() uses for requests that are too big
            setParseFailedReason(FailReason.TOO_MANY_PARAMETERS);
            throw new IllegalStateException(sm.getString(
                    "parameters.maxCountFail", Integer.valueOf(limit)));
        }

        ArrayList<String> values = paramHashValues.get(key);
        if (values == null) {
            values = new ArrayList<>(1);
            paramHashValues.put(key, values);
        }
        values.add(value);
    }

而后再这里调用

public Enumeration<String> getParameterNames() {
        handleQueryParameters();
        return Collections.enumeration(paramHashValues.keySet());
    }

而Request的getParameterNames则委托Parameters的getParameterNames

public Enumeration<String> getParameterNames() {

        if (!parametersParsed) {
            parseParameters();
        }

        return coyoteRequest.getParameters().getParameterNames();

    }

最后，有个统一的merge过程，见上头的mergeParameters。

usingReader以及usingInputStream标志位

getReader

@Override
    public BufferedReader getReader() throws IOException {

        if (usingInputStream) {
            throw new IllegalStateException
                (sm.getString("coyoteRequest.getReader.ise"));
        }

        usingReader = true;
        inputBuffer.checkConverter();
        if (reader == null) {
            reader = new CoyoteReader(inputBuffer);
        }
        return reader;

    }

getInputStream

@Override
    public ServletInputStream getInputStream() throws IOException {

        if (usingReader) {
            throw new IllegalStateException
                (sm.getString("coyoteRequest.getInputStream.ise"));
        }

        usingInputStream = true;
        if (inputStream == null) {
            inputStream = new CoyoteInputStream(inputBuffer);
        }
        return inputStream;

    }

Servlet Request的 getInputStream() getReader() getParameter()，在读取post方法的参数时，使用了任意一个，再调用其余两个方法是读取不到参数的。getParameter单线程上可重复使用，多线程的话可能会有异常，由于该方法依赖parametersParsed，这个boolean的参数不是原子的。

docs

• Servlet Request的 getInputStream() getReader() getParameter()