@RequestMapping(value = "/a2")
    @ResponseBody
    public String hello3(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) {
        String string = httpServletRequest.getParameter("json");
        System.out.println(string);
        return "hahah";
    }

@RequestMapping(value = "/a")
    @ResponseBody
    public void hello1(@RequestBody String string) {
        System.out.println(string);
    }

 
package org.apache.catalina.connector;
public class Request
     @Override
    public String getParameter(String name) {
        if (!parametersParsed) {
            parseParameters();
        }
        return coyoteRequest.getParameters().getParameter(name);
    }
	/**
     * 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);
                }
            }
		.....
		省略
		.....
    }
	/**
     * Get the character encoding used for this request.
     */
    public String getCharacterEncoding() {
        if (charEncoding != null)
            return charEncoding;
        charEncoding = ContentType.getCharsetFromContentType(getContentType());
        return charEncoding;
    }
}

package org.apache.tomcat.util.http;
public class ContentType {
    /**
     * Parse the character encoding from the specified content type header.
     * If the content type is null, or there is no explicit character encoding,
     * <code>null</code> is returned.
     *
     * @param contentType a content type header
     */
    public static String getCharsetFromContentType(String contentType) {
        if (contentType == null) {
            return (null);
        }
        int start = contentType.indexOf("charset=");
        if (start < 0) {
            return (null);
        }
        String encoding = contentType.substring(start + 8);
        int end = encoding.indexOf(';');
        if (end >= 0) {
            encoding = encoding.substring(0, end);
        }
        encoding = encoding.trim();
        if ((encoding.length() > 2) && (encoding.startsWith("\""))
            && (encoding.endsWith("\""))) {
            encoding = encoding.substring(1, encoding.length() - 1);
        }
        return (encoding.trim());
    }
}

package org.apache.coyote;
public final class Constants {
    // -------------------------------------------------------------- Constants
    public static final String Package = "org.apache.coyote";
    public static final String DEFAULT_CHARACTER_ENCODING="ISO-8859-1";
	...
	省略
	...
}