Servlet The Request
The Request
HTTP Protocol Parameters
所有的HTTP Protocol Parameters都会放在一个Map中, 可以通过getParameterMap得到. 对于Query String和Post Body中的请求, 会将两者放在同一个set中, Query String的顺序靠前.
query string: a = hello
post body: a = goodbye & a = world
result set: a = (hello, goodbye, world)
而通过GET方式拼在url后面的参数不会在这里体现, 是通过getRequestURI()和getPathInfo()得到的.
如果符合下列情况, 则可以在参数Map中得到参数:
- HTTP or HTTPS
- HTTP Method: POST
- Content Type: application/x-www-form-urlencoded
- Servlet被正确创建和实例化, 并调用getParameters方法族.
如果不符合以上条件, 还可以从Request的InputStream中读取, 而满足条件后InputStream不能读出数据.
File Upload
如果Request的Type是"multipart/form-data", 并且处理的servlet上加了"@MultipartConfig", 那么HttpServletRequest可以通过以下函数处理文件上传:
public Collection<Part> getParts()
public Part getPart(String name).
并且每一个Part都可以取的头信息, Type, 并通过getInputStream取的内容.
又因为使用了form-data的形式, 其实也可以通过getParameter的方式得到内容.
Attributes
Attributes是和Request相关的信息, 但是可以由container访问到, 比如可以使用在两个servlet的通信中, 可以通过下列方法访问. 一般Attributes的命名也使用倒序的文件结构名.
getAttribute
getAttributeNames
setAttribute
Headers
Request Path Elements
Request Path Elements包含几个部分, 有:
- Context Path
- Servlet Path
- PathInfo
requestURI = contextPath + servletPath + pathInfo
Servlet的配置信息:
Context Path /catalog
Servlet Mapping Pattern: /lawn/*
Servlet: LawnServlet
Servlet Mapping Pattern: /garden/*
Servlet: GardenServlet
Servlet Mapping Pattern: *.jsp
Servlet: JSPServlet
访问的URL示例:
/catalog/lawn/index.html ContextPath: /catalog
ServletPath: /lawn
PathInfo: /index.html
/catalog/garden/implements/ ContextPath: /catalog
ServletPath: /garden
PathInfo: /implements/
/catalog/help/feedback.jsp ContextPath: /catalog
ServletPath: /help/feedback.jsp
PathInfo: null
Path Translation Methods
可以通过两个函数得到真实的Servlet对应的文件系统的信息:
- ServletContext.getRealPath
- HttpServletRequest.getPathTranslated
返回本地的文件系统的路径, 如果是远程或者是得不到则返回null.
Resources inside the META-INF/resources directory of JAR file must be
considered only if the container has unpacked them from their containing JAR file
when a call to getRealPath() is made, and in this case MUST return the unpacked
location.
SSL Attributes
如果Request使用了secure protocol, 如HTTPS. 下列信息必须由Web Container暴露给Servlet
| Attribute | Attribute Name | Java Type |
|---|---|---|
| cipher suite | javax.servlet.request.cipher_suite | String |
| bit size of the algorithm | javax.servlet.request.key_size | Integer |
| SSL session id | javax.servlet.request.ssl_session_id | String |
Lifetime of the Request Object
Each request object is valid only within the scope of a servlet’s service method, or
within the scope of a filter’s doFilter method, unless the asynchronous processing
is enabled for the component and the startAsync method is invoked on the request
object.
