The HTTP Connector
https://tomcat.apache.org/tomcat-7.0-doc/config/http.html
The standard HTTP connectors (BIO, NIO and APR/native) all support the following attributes in addition to the common Connector attributes listed above.
| Attribute | Description |
|---|---|
acceptCount |
The maximum queue length for incoming connection requests when all possible request processing threads are in use. Any requests received when the queue is full will be refused. The default value is 100. |
acceptorThreadCount |
The number of threads to be used to accept connections. Increase this value on a multi CPU machine, although you would never really need more than |
acceptorThreadPriority |
The priority of the acceptor threads. The threads used to accept new connections. The default value is |
address |
For servers with more than one IP address, this attribute specifies which address will be used for listening on the specified port. By default, this port will be used on all IP addresses associated with the server. |
allowHostHeaderMismatch |
By default Tomcat will allow requests that specify a host in the request line but specify a different host in the host header. This check can be enabled by setting this attribute to |
allowedTrailerHeaders |
By default Tomcat will ignore all trailer headers when processing chunked input. For a header to be processed, it must be added to this comma-separated list of header names. |
bindOnInit |
Controls when the socket used by the connector is bound. By default it is bound when the connector is initiated and unbound when the connector is destroyed. If set to |
compressibleMimeType |
The value is a comma separated list of MIME types for which HTTP compression may be used. The default value is |
compression |
The Connector may use HTTP/1.1 GZIP compression in an attempt to save server bandwidth. The acceptable values for the parameter is "off" (disable compression), "on" (allow compression, which causes text data to be compressed), "force" (forces compression in all cases), or a numerical integer value (which is equivalent to "on", but specifies the minimum amount of data before the output is compressed). If the content-length is not known and compression is set to "on" or more aggressive, the output will also be compressed. If not specified, this attribute is set to "off". Note: There is a tradeoff between using compression (saving your bandwidth) and using the sendfile feature (saving your CPU cycles). If the connector supports the sendfile feature, e.g. the NIO connector, using sendfile will take precedence over compression. The symptoms will be that static files greater that 48 Kb will be sent uncompressed. You can turn off sendfile by setting |
compressionMinSize |
If compression is set to "on" then this attribute may be used to specify the minimum amount of data before the output is compressed. If not specified, this attribute is defaults to "2048". |
connectionLinger |
The number of seconds during which the sockets used by this Connector will linger when they are closed. The default value is |
connectionTimeout |
The number of milliseconds this Connector will wait, after accepting a connection, for the request URI line to be presented. Use a value of -1 to indicate no (i.e. infinite) timeout. The default value is 60000 (i.e. 60 seconds) but note that the standard server.xml that ships with Tomcat sets this to 20000 (i.e. 20 seconds). Unless disableUploadTimeout is set to |
connectionUploadTimeout |
Specifies the timeout, in milliseconds, to use while a data upload is in progress. This only takes effect if disableUploadTimeout is set to |
disableUploadTimeout |
This flag allows the servlet container to use a different, usually longer connection timeout during data upload. If not specified, this attribute is set to |
executor |
A reference to the name in an Executor element. If this attribute is set, and the named executor exists, the connector will use the executor, and all the other thread attributes will be ignored. Note that if a shared executor is not specified for a connector then the connector will use a private, internal executor to provide the thread pool. |
executorTerminationTimeoutMillis |
The time that the private internal executor will wait for request processing threads to terminate before continuing with the process of stopping the connector. If not set, the default is |
keepAliveTimeout |
The number of milliseconds this Connector will wait for another HTTP request before closing the connection. The default value is to use the value that has been set for the connectionTimeout attribute. Use a value of -1 to indicate no (i.e. infinite) timeout. |
maxConnections |
The maximum number of connections that the server will accept and process at any given time. When this number has been reached, the server will accept, but not process, one further connection. This additional connection be blocked until the number of connections being processed falls below maxConnections at which point the server will start accepting and processing new connections again. Note that once the limit has been reached, the operating system may still accept connections based on the Note that for APR/native on Windows, the configured value will be reduced to the highest multiple of 1024 that is less than or equal to maxConnections. This is done for performance reasons. |
maxCookieCount |
The maximum number of cookies that are permitted for a request. A value of less than zero means no limit. If not specified, a default value of 200 will be used. |
maxExtensionSize |
Limits the total length of chunk extensions in chunked HTTP requests. If the value is |
maxHttpHeaderSize |
The maximum size of the request and response HTTP header, specified in bytes. If not specified, this attribute is set to 8192 (8 KB). |
maxKeepAliveRequests |
The maximum number of HTTP requests which can be pipelined until the connection is closed by the server. Setting this attribute to 1 will disable HTTP/1.0 keep-alive, as well as HTTP/1.1 keep-alive and pipelining. Setting this to -1 will allow an unlimited amount of pipelined or keep-alive HTTP requests. If not specified, this attribute is set to 100. |
maxSwallowSize |
The maximum number of request body bytes (excluding transfer encoding overhead) that will be swallowed by Tomcat for an aborted upload. An aborted upload is when Tomcat knows that the request body is going to be ignored but the client still sends it. If Tomcat does not swallow the body the client is unlikely to see the response. If not specified the default of 2097152 (2 megabytes) will be used. A value of less than zero indicates that no limit should be enforced. |
maxThreads |
The maximum number of request processing threads to be created by this Connector, which therefore determines the maximum number of simultaneous requests that can be handled. If not specified, this attribute is set to 200. If an executor is associated with this connector, this attribute is ignored as the connector will execute tasks using the executor rather than an internal thread pool. Note that if an executor is configured any value set for this attribute will be recorded correctly but it will be reported (e.g. via JMX) as |
maxTrailerSize |
Limits the total length of trailing headers in the last chunk of a chunked HTTP request. If the value is |
minSpareThreads |
The minimum number of threads always kept running. This includes both active and idle threads. If not specified, the default of |
noCompressionUserAgents |
The value is a regular expression (using |
processorCache |
The protocol handler caches Processor objects to speed up performance. This setting dictates how many of these objects get cached. |
rejectIllegalHeaderName |
If an HTTP request is received that contains an illegal header name (i.e. the header name is not a token) this setting determines if the request will be rejected with a 400 response ( |
relaxedPathChars |
The HTTP/1.1 specification requires that certain characters are %nn encoded when used in URI paths. Unfortunately, many user agents including all the major browsers are not compliant with this specification and use these characters in unencoded form. To prevent Tomcat rejecting such requests, this attribute may be used to specify the additional characters to allow. If not specified, no additional characters will be allowed. The value may be any combination of the following characters: |
relaxedQueryChars |
The HTTP/1.1 specification requires that certain characters are %nn encoded when used in URI query strings. Unfortunately, many user agents including all the major browsers are not compliant with this specification and use these characters in unencoded form. To prevent Tomcat rejecting such requests, this attribute may be used to specify the additional characters to allow. If not specified, no additional characters will be allowed. The value may be any combination of the following characters: |
restrictedUserAgents |
The value is a regular expression (using |
server |
Overrides the Server header for the http response. If set, the value for this attribute overrides the Tomcat default and any Server header set by a web application. If not set, any value specified by the application is used. If the application does not specify a value then |
socketBuffer |
The size (in bytes) of the buffer to be provided for socket output buffering. -1 can be specified to disable the use of a buffer. By default, a buffers of 9000 bytes will be used. |
SSLEnabled |
Use this attribute to enable SSL traffic on a connector. To turn on SSL handshake/encryption/decryption on a connector set this value to |
tcpNoDelay |
If set to |
threadPriority |
The priority of the request processing threads within the JVM. The default value is |
upgradeAsyncWriteBufferSize |
The default size of the buffer to allocate to for asynchronous writes that can not be completed in a single operation, specified in bytes. Data that can't be written immediately will be stored in this buffer until it can be written. If more data needs to be stored than space is available in the buffer than the size of the buffer will be increased for the duration of the write. If not specified the default value of 8192 will be used. |
其中maxConnections描述红色部分说明当连接数达到最大值后，系统会继续接收连接但不会超过acceptCount的值。
理解：
我们可以把tomcat比做一个电影院，流程是取号、买票、观影，acceptCount比作前厅(容纳取到号的人)、maxConnections比作大厅（容纳买到票的人）、maxThreads比作影厅（可以理解一个影厅只容纳一个人，因为一个线程同时只处理一个请求），以下场景是针对已达到maxConnections最大值来讨论的
1）取号：如果前厅人数已达到acceptCount，则拿号失败，会得到Connection refused connect的回复信息。反之则会进入前厅，等待买票。
2）买票：当大厅人数小于maxConnections时，前厅的人就可以进入大厅
3）观影：当影厅的人离开时，大厅的部分人能进入影厅，一般来讲大厅的容量要远大于影厅的数量。
本文是针对apache-tomcat-7.0.55做的测试。
tomcat server.xml配置参数
<Connector port="8080" protocol="org.apache.coyote.http11.Http11NioProtocol" acceptCount="2" maxConnections="10" maxThreads="2"
connectionTimeout="20000"
redirectPort="8443" />
Servlet的代码：休眠20秒
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
InputStream is = request.getInputStream();
System.out.println(new Date()+":"+is+"开始");
Thread.sleep(20000);
System.out.println(new Date()+":"+is+"结束");
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
一个请求或一个connection的生命周期：可以简单的理解为从doGet或doPost开始response响应结束。
使用JMeter测试，线程数20，连接超时时间10s，响应超时时间30s
测试结果：
察看结果数：
第1秒：8个请求得到响应数据：Connection refused connect
第20秒：2个请求正常响应
第30秒：剩余10个请求得到响应数据：Readtimed out
tomcat日志：
打印12组开始结束的日志，说明tomcat会处理acceptCount+maxConnections的请求，说明只要取到号，有足够的耐心，就肯定能够看到电影。
部分原文：https://blog.csdn.net/kaka20099527/article/details/53285348