- getContext
- getMajorVersion
- getMinorVersion
- getMimeType
- getResourcePaths
- getResource
- getResourceAsStream
- getRequestDispatcher
- getNamedDispatcher
- getServlet
- getServlets
- getServletNames
- log
- log
- log
- getRealPath
- getServerInfo
- getInitParameter
- getInitParameterNames
- getAttribute
- getAttributeNames
- setAttribute
- removeAttribute
- getServletContextName
- getServletName
- getServletContext
- getInitParameter
- getInitParameterNames
ServletContext对象:
对于web容器来说,ServletContext接口定义了一个servlet环境对象,这个对象定义了一个在servlet引擎上的servlet的视图。通过使用这个对象,servlet可以记录事件,得到资源并得到来自servlet的引擎类。
servlet容器在启动时会加载web应用,并为每个web应用创建唯一的servlet context对象,可以把ServletContext看成是一个Web应用的服务器端组件的共享内存,在ServletContext中可以存放共享数据,他提供了4个读取和设置共享数据的方法。
对任何servlet,任何人在任何时间都有效,这才是真正全局的对象。一般来说,对整个应用的配置,为了不使用“硬编码”,应该配置为ServletContext参数,比如字 符集设定。
<web-app>
.................
<init-param>
<param-name>charset</param-name>
<param-value>GB2312</param-value>
</init-param>
.................
</web-app>
最后针对ServletContext我自己的总结是:
ServletContext即servlet容器,其内提供的方法可以在同一web应用下的所有servlet中被使用
ServletConfig对象:
从一个servlet被实例化后,对任何客户端在任何时候访问有效,但仅对本servlet 有效,一个servlet的ServletConfig对象不能被另一个servlet访问。 因此只有一个特定的servlet要设定的参数,应该配置为ServletConfig
参数,如一个读取附件的servlet要用到绝对目录,而别的servlet不会用到:
<servlet>
<servlet-name>GetAtt</servlet-name>
<servlet-class>mail.GetAttServlet</servlet-class>
<init-param>
<param-name>absPath</param-name>
<param-value>/usr/mail/ax/axman/Maildir/</param-value>
</init-param>
</servlet>
如上,因为在<servlet>标签中已经指定了name和class,也就是说只有mail.GetAttServlet这个
servlet中才能取到path,而别的Servlet是不能取到的。
如何获取这两个对象的参数:
访问ServletConfig参数:
首先要取得ServletConfig对象,然后调用它的getInitParameter();方法。要访问
ServletConfig对象,jsp中直接使用config内置对象,但因为你的JSP编译后的servlet一般不会被
加到web.xml中的,所以一般不会通过jsp来取对本JSP编译后的servlet的配置参数,那么在servlet
中要得到ServletConfig对象有两种方法:
在inii()方法中取到:通过init的重载方法传递
.....
public class Test extends HttpServlet
{
ServletConfig config;
public void init(ServletConfig config) throws ServletException {
this.config = config;
}
..................
}
然后在下面的方法中就可以访问config对象。但要注意,为了确保能从构造方法中到当前servlet的
config对象,应该调用父类的构造方法:
.....
public class Test extends HttpServlet
{
ServletConfig config;
public void init(ServletConfig config) throws ServletException {
super.init(config);
this.config = config;
}
..................
}
通过getServletConfig()方法直接到时,这样做的好处是不必调手工传递属性,想在任何时候都可
以得到。
还有第三种方法,要自己实现一些接口,这里作为一般讨论就不介绍了。
要访问ServletContext对象,只要从现有的ServletConfig对象getServletContext()就可以了,然后/r调用它的getInitParameter()方法就可以获取它的参数。
按说:ServletContext对象的作用域比ServletConfig作用域大,为什么要从ServletConfig中到得
ServletContext对象呢?我个人认为:容器保存了很多个ServletContext对象,请求时容器到底取哪一个/r给你呢?那就取其中包含ServletConfig信息的那个给你,就是说取ServletConfig对象的父级对象。就好象HttpSession要从requset中取得一样,就是取那个包含当前request对象的session对象给你,这只是我的个人想法。
附两个对象 的API参考:
Method Detail |
getContext
public ServletContext getContext(java.lang.String uripath)
- Returns a
ServletContext
object that corresponds to a specified URL on the server.This method allows servlets to gain access to the context for various parts of the server, and as needed obtain
RequestDispatcher
objects from the context. The given path must be begin with "/", is interpreted relative to the server's document root and is matched against the context roots of other web applications hosted on this container.In a security conscious environment, the servlet container may return
null
for a given URL.- Parameters:
uripath
- aString
specifying the context path of another web application in the container.- Returns:
- the
ServletContext
object that corresponds to the named URL, or null if either none exists or the container wishes to restrict this access. - See Also:
RequestDispatcher
getMajorVersion
public int getMajorVersion()
- Returns the major version of the Java Servlet API that this servlet container supports. All implementations that comply with Version 2.3 must have this method return the integer 2.
- Returns:
- 2
getMinorVersion
public int getMinorVersion()
- Returns the minor version of the Servlet API that this servlet container supports. All implementations that comply with Version 2.3 must have this method return the integer 3.
- Returns:
- 3
getMimeType
public java.lang.String getMimeType(java.lang.String file)
- Returns the MIME type of the specified file, or
null
if the MIME type is not known. The MIME type is determined by the configuration of the servlet container, and may be specified in a web application deployment descriptor. Common MIME types are"text/html"
and"image/gif"
.- Parameters:
file
- aString
specifying the name of a file- Returns:
- a
String
specifying the file's MIME type
getResourcePaths
public java.util.Set getResourcePaths(java.lang.String path)
- Returns a directory-like listing of all the paths to resources within the web application whose longest sub-path matches the supplied path argument. Paths indicating subdirectory paths end with a '/'. The returned paths are all relative to the root of the web application and have a leading '/'. For example, for a web application containing
/welcome.html
/catalog/index.html
/catalog/products.html
/catalog/offers/books.html
/catalog/offers/music.html
/customer/login.jsp
/WEB-INF/web.xml
/WEB-INF/classes/com.acme.OrderServlet.class,getResourcePaths("/") returns {"/welcome.html", "/catalog/", "/customer/", "/WEB-INF/"}
getResourcePaths("/catalog/") returns {"/catalog/index.html", "/catalog/products.html", "/catalog/offers/"}.- Parameters:
the
- partial path used to match the resources, which must start with a /- Returns:
- a Set containing the directory listing, or null if there are no resources in the web application whose path begins with the supplied path.
- Since:
- Servlet 2.3
getResource
public java.net.URL getResource(java.lang.String path) throws java.net.MalformedURLException
- Returns a URL to the resource that is mapped to a specified path. The path must begin with a "/" and is interpreted as relative to the current context root.
This method allows the servlet container to make a resource available to servlets from any source. Resources can be located on a local or remote file system, in a database, or in a
.war
file.The servlet container must implement the URL handlers and
URLConnection
objects that are necessary to access the resource.This method returns
null
if no resource is mapped to the pathname.Some containers may allow writing to the URL returned by this method using the methods of the URL class.
The resource content is returned directly, so be aware that requesting a
.jsp
page returns the JSP source code. Use aRequestDispatcher
instead to include results of an execution.This method has a different purpose than
java.lang.Class.getResource
, which looks up resources based on a class loader. This method does not use class loaders.- Parameters:
path
- aString
specifying the path to the resource- Returns:
- the resource located at the named path, or
null
if there is no resource at that path - Throws:
- java.net.MalformedURLException - if the pathname is not given in the correct form
getResourceAsStream
public java.io.InputStream getResourceAsStream(java.lang.String path)
- Returns the resource located at the named path as an
InputStream
object.The data in the
InputStream
can be of any type or length. The path must be specified according to the rules given ingetResource
. This method returnsnull
if no resource exists at the specified path.Meta-information such as content length and content type that is available via
getResource
method is lost when using this method.The servlet container must implement the URL handlers and
URLConnection
objects necessary to access the resource.This method is different from
java.lang.Class.getResourceAsStream
, which uses a class loader. This method allows servlet containers to make a resource available to a servlet from any location, without using a class loader.- Parameters:
name
- aString
specifying the path to the resource- Returns:
- the
InputStream
returned to the servlet, ornull
if no resource exists at the specified path
getRequestDispatcher
public RequestDispatcher getRequestDispatcher(java.lang.String path)
- Returns a
RequestDispatcher
object that acts as a wrapper for the resource located at the given path. ARequestDispatcher
object can be used to forward a request to the resource or to include the resource in a response. The resource can be dynamic or static.The pathname must begin with a "/" and is interpreted as relative to the current context root. Use
getContext
to obtain aRequestDispatcher
for resources in foreign contexts. This method returnsnull
if theServletContext
cannot return aRequestDispatcher
.- Parameters:
path
- aString
specifying the pathname to the resource- Returns:
- a
RequestDispatcher
object that acts as a wrapper for the resource at the specified path - See Also:
RequestDispatcher
,getContext(java.lang.String)
getNamedDispatcher
public RequestDispatcher getNamedDispatcher(java.lang.String name)
- Returns a
RequestDispatcher
object that acts as a wrapper for the named servlet.Servlets (and JSP pages also) may be given names via server administration or via a web application deployment descriptor. A servlet instance can determine its name using
ServletConfig.getServletName()
.This method returns
null
if theServletContext
cannot return aRequestDispatcher
for any reason.- Parameters:
name
- aString
specifying the name of a servlet to wrap- Returns:
- a
RequestDispatcher
object that acts as a wrapper for the named servlet - See Also:
RequestDispatcher
,getContext(java.lang.String)
,ServletConfig.getServletName()
getServlet
public Servlet getServlet(java.lang.String name) throws ServletException
- Deprecated. As of Java Servlet API 2.1, with no direct replacement.
This method was originally defined to retrieve a servlet from a
ServletContext
. In this version, this method always returnsnull
and remains only to preserve binary compatibility. This method will be permanently removed in a future version of the Java Servlet API.In lieu of this method, servlets can share information using the
ServletContext
class and can perform shared business logic by invoking methods on common non-servlet classes.
getServlets
public java.util.Enumeration getServlets()
- Deprecated. As of Java Servlet API 2.0, with no replacement.
This method was originally defined to return an
Enumeration
of all the servlets known to this servlet context. In this version, this method always returns an empty enumeration and remains only to preserve binary compatibility. This method will be permanently removed in a future version of the Java Servlet API.
getServletNames
public java.util.Enumeration getServletNames()
- Deprecated. As of Java Servlet API 2.1, with no replacement.
This method was originally defined to return an
Enumeration
of all the servlet names known to this context. In this version, this method always returns an emptyEnumeration
and remains only to preserve binary compatibility. This method will be permanently removed in a future version of the Java Servlet API.
log
public void log(java.lang.String msg)
- Writes the specified message to a servlet log file, usually an event log. The name and type of the servlet log file is specific to the servlet container.
- Parameters:
msg
- aString
specifying the message to be written to the log file
log
public void log(java.lang.Exception exception, java.lang.String msg)
- Deprecated. As of Java Servlet API 2.1, use
log(String message, Throwable throwable)
instead.
This method was originally defined to write an exception's stack trace and an explanatory error message to the servlet log file.
log
public void log(java.lang.String message, java.lang.Throwable throwable)
- Writes an explanatory message and a stack trace for a given
Throwable
exception to the servlet log file. The name and type of the servlet log file is specific to the servlet container, usually an event log.- Parameters:
message
- aString
that describes the error or exceptionthrowable
- theThrowable
error or exception
getRealPath
public java.lang.String getRealPath(java.lang.String path)
- Returns a
String
containing the real path for a given virtual path. For example, the path "/index.html" returns the absolute file path on the server's filesystem would be served by a request for "http://host/contextPath/index.html", where contextPath is the context path of this ServletContext..The real path returned will be in a form appropriate to the computer and operating system on which the servlet container is running, including the proper path separators. This method returns
null
if the servlet container cannot translate the virtual path to a real path for any reason (such as when the content is being made available from a.war
archive).- Parameters:
path
- aString
specifying a virtual path- Returns:
- a
String
specifying the real path, or null if the translation cannot be performed
getServerInfo
public java.lang.String getServerInfo()
- Returns the name and version of the servlet container on which the servlet is running.
The form of the returned string is servername/versionnumber. For example, the JavaServer Web Development Kit may return the string
JavaServer Web Dev Kit/1.0
.The servlet container may return other optional information after the primary string in parentheses, for example,
JavaServer Web Dev Kit/1.0 (JDK 1.1.6; Windows NT 4.0 x86)
.- Returns:
- a
String
containing at least the servlet container name and version number
getInitParameter
public java.lang.String getInitParameter(java.lang.String name)
- Returns a
String
containing the value of the named context-wide initialization parameter, ornull
if the parameter does not exist.This method can make available configuration information useful to an entire "web application". For example, it can provide a webmaster's email address or the name of a system that holds critical data.
- Parameters:
name
- aString
containing the name of the parameter whose value is requested- Returns:
- a
String
containing at least the servlet container name and version number - See Also:
ServletConfig.getInitParameter(java.lang.String)
getInitParameterNames
public java.util.Enumeration getInitParameterNames()
- Returns the names of the context's initialization parameters as an
Enumeration
ofString
objects, or an emptyEnumeration
if the context has no initialization parameters.- Returns:
- an
Enumeration
ofString
objects containing the names of the context's initialization parameters - See Also:
ServletConfig.getInitParameter(java.lang.String)
getAttribute
public java.lang.Object getAttribute(java.lang.String name)
- Returns the servlet container attribute with the given name, or
null
if there is no attribute by that name. An attribute allows a servlet container to give the servlet additional information not already provided by this interface. See your server documentation for information about its attributes. A list of supported attributes can be retrieved usinggetAttributeNames
.The attribute is returned as a
java.lang.Object
or some subclass. Attribute names should follow the same convention as package names. The Java Servlet API specification reserves names matchingjava.*
,javax.*
, andsun.*
.- Parameters:
name
- aString
specifying the name of the attribute- Returns:
- an
Object
containing the value of the attribute, ornull
if no attribute exists matching the given name - See Also:
getAttributeNames()
getAttributeNames
public java.util.Enumeration getAttributeNames()
- Returns an
Enumeration
containing the attribute names available within this servlet context. Use thegetAttribute(java.lang.String)
method with an attribute name to get the value of an attribute.- Returns:
- an
Enumeration
of attribute names - See Also:
getAttribute(java.lang.String)
setAttribute
public void setAttribute(java.lang.String name, java.lang.Object object)
- Binds an object to a given attribute name in this servlet context. If the name specified is already used for an attribute, this method will replace the attribute with the new to the new attribute.
If listeners are configured on the
ServletContext
the container notifies them accordingly.If a null value is passed, the effect is the same as calling
removeAttribute()
.Attribute names should follow the same convention as package names. The Java Servlet API specification reserves names matching
java.*
,javax.*
, andsun.*
.- Parameters:
name
- aString
specifying the name of the attributeobject
- anObject
representing the attribute to be bound
removeAttribute
public void removeAttribute(java.lang.String name)
- Removes the attribute with the given name from the servlet context. After removal, subsequent calls to
getAttribute(java.lang.String)
to retrieve the attribute's value will returnnull
.If listeners are configured on the
ServletContext
the container notifies them accordingly.- Parameters:
name
- aString
specifying the name of the attribute to be removed
getServletContextName
public java.lang.String getServletContextName()
- Returns the name of this web application correponding to this ServletContext as specified in the deployment descriptor for this web application by the display-name element.
- Returns:
- The name of the web application or null if no name has been declared in the deployment descriptor.
- Since:
- Servlet 2.3
Interface ServletConfig
Method Detail |
getServletName
public java.lang.String getServletName()
- Returns the name of this servlet instance. The name may be provided via server administration, assigned in the web application deployment descriptor, or for an unregistered (and thus unnamed) servlet instance it will be the servlet's class name.
- Returns:
- the name of the servlet instance
getServletContext
public ServletContext getServletContext()
- Returns a reference to the
ServletContext
in which the caller is executing.- Returns:
- a
ServletContext
object, used by the caller to interact with its servlet container - See Also:
ServletContext
getInitParameter
public java.lang.String getInitParameter(java.lang.String name)
- Returns a
String
containing the value of the named initialization parameter, ornull
if the parameter does not exist.- Parameters:
name
- aString
specifying the name of the initialization parameter- Returns:
- a
String
containing the value of the initialization parameter
getInitParameterNames
public java.util.Enumeration getInitParameterNames()
- Returns the names of the servlet's initialization parameters as an
Enumeration
ofString
objects, or an emptyEnumeration
if the servlet has no initialization parameters.- Returns:
- an
Enumeration
ofString
objects containing the names of the servlet's initialization parameters