搜云库技术团队
前言
开心一刻
过年女婿来岳父家走亲戚，当时小舅子主就问：姐夫，你什么时候能给我姐幸福，让我姐好好享受生活的美好。你们这辈子不准备买一套大点的房子吗？姐夫说：现在没钱啊！不过我有一个美丽可爱的女儿，等长大后找个有钱的老公嫁了，那时我就能和你姐一起住大房子了。岳父不乐意的说了一句：当初我也是这么认为的，可惜未能如愿。
路漫漫其修远兮，吾将上下而求索！
github：https://github.com/youzhibing
码云(gitee)：https://gitee.com/youzhibing
ServletContext
ServletContext介绍
定义了servlet与其servlet容器通信的一些列方法，例如，获取文件的MIME类型，分派请求或写入日志文件。
Servlet的运行模式是一个典型的“握手型的交互式”运行模式。所谓“握手型的交互式”就是两个模块为了交换数据通常都会准备一个交易场景，这个场景一直跟随这个交易过程直到这个交易完成为止。这个交易场景的初始化是根据这次交易对象指定的参数来定制的，这些制定参数通常就是一个配置类。所以对号入座，交易场景由ServletContext来描述，而定制的参数集合由ServletConfig来描述。而ServletRequest和ServletResponse就是要交互的具体对象，它们通常都作为运输工具来传递交互结果。ServletContext，即servlet上下文，用于存放web应用信息；每个Java虚拟机每个Web项目只有一个ServletContext，它是由Web服务器创建，代表当前web应用。
Servlet 3.0规范之前
我们采用2.5来看下源码
maven依赖
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
<scope>provided</scope>
</dependency>
View Code
源码
/*
* The contents of this file are subject to the terms
* of the Common Development and Distribution License
* (the "License"). You may not use this file except
* in compliance with the License.
*
* You can obtain a copy of the license at
* glassfish/bootstrap/legal/CDDLv1.0.txt or
* https://glassfish.dev.java.net/public/CDDLv1.0.html.
* See the License for the specific language governing
* permissions and limitations under the License.
*
* When distributing Covered Code, include this CDDL
* HEADER in each file and include the License file at
* glassfish/bootstrap/legal/CDDLv1.0.txt. If applicable,
* add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your
* own identifying information: Portions Copyright [yyyy]
* [name of copyright owner]
*
* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
*
* Portions Copyright Apache Software Foundation.
*/
package javax.servlet;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Set;
/**
*
* Defines a set of methods that a servlet uses to communicate with its
* servlet container, for example, to get the MIME type of a file, dispatch
* requests, or write to a log file.
*
* <p>There is one context per "web application" per Java Virtual Machine. (A
* "web application" is a collection of servlets and content installed under a
* specific subset of the server's URL namespace such as <code>/catalog</code>
* and possibly installed via a <code>.war</code> file.)
*
* <p>In the case of a web
* application marked "distributed" in its deployment descriptor, there will
* be one context instance for each virtual machine. In this situation, the
* context cannot be used as a location to share global information (because
* the information won't be truly global). Use an external resource like
* a database instead.
*
* <p>The <code>ServletContext</code> object is contained within
* the {@link ServletConfig} object, which the Web server provides the
* servlet when the servlet is initialized.
*
* @author Various
*
* @see Servlet#getServletConfig
* @see ServletConfig#getServletContext
*
*/
public interface ServletContext {
/**
* Returns the context path of the web application.
*
* <p>The context path is the portion of the request URI that is used
* to select the context of the request. The context path always comes
* first in a request URI. The path starts with a "/" character but does
* not end with a "/" character. For servlets in the default (root)
* context, this method returns "".
*
* <p>It is possible that a servlet container may match a context by
* more than one context path. In such cases the
* {@link javax.servlet.http.HttpServletRequest#getContextPath()}
* will return the actual context path used by the request and it may
* differ from the path returned by this method.
* The context path returned by this method should be considered as the
* prime or preferred context path of the application.
*
* @return The context path of the web application, or "" for the
* default (root) context
*
* @see javax.servlet.http.HttpServletRequest#getContextPath()
*
* @since Servlet 2.5
*/
public String getContextPath();
/**
* Returns a <code>ServletContext</code> object that
* corresponds to a specified URL on the server.
*
* <p>This method allows servlets to gain
* access to the context for various parts of the server, and as
* needed obtain {@link 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.
*
* <p>In a security conscious environment, the servlet container may
* return <code>null</code> for a given URL.
*
* @param uripath a <code>String</code> specifying the context path of
* another web application in the container.
* @return the <code>ServletContext</code> object that
* corresponds to the named URL, or null if either
none exists or the container wishes to restrict
* this access.
*
* @see RequestDispatcher
*
*/
public ServletContext getContext(String uripath);
/**
* Returns the major version of the Java Servlet API that this
* servlet container supports. All implementations that comply
* with Version 2.5 must have this method
* return the integer 2.
*
* @return 2
*
*/
public int getMajorVersion();
/**
* Returns the minor version of the Servlet API that this
* servlet container supports. All implementations that comply
* with Version 2.5 must have this method
* return the integer 5.
*
* @return 5
*
*/
public int getMinorVersion();
/**
* Returns the MIME type of the specified file, or <code>null</code> 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 <code>"text/html"</code> and <code>"image/gif"</code>.
*
*
* @param file a <code>String</code> specifying the name
* of a file
*
* @return a <code>String</code> specifying the file's MIME type
*
*/
public String getMimeType(String file);
/**
* 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<br><br>
* /welcome.html<br>
* /catalog/index.html<br>
* /catalog/products.html<br>
* /catalog/offers/books.html<br>
* /catalog/offers/music.html<br>
* /customer/login.jsp<br>
* /WEB-INF/web.xml<br>
* /WEB-INF/classes/com.acme.OrderServlet.class,<br><br>
*
* getResourcePaths("/") returns {"/welcome.html", "/catalog/", "/customer/", "/WEB-INF/"}<br>
* getResourcePaths("/catalog/") returns {"/catalog/index.html", "/catalog/products.html", "/catalog/offers/"}.<br>
*@param path the partial path used to match the resources,
* which must start with a /
*@return 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
*/
public Set getResourcePaths(String path);
/**
* 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.
*
* <p>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 <code>.war</code> file.
*
* <p>The servlet container must implement the URL handlers
* and <code>URLConnection</code> objects that are necessary
* to access the resource.
*
* <p>This method returns <code>null</code>
* if no resource is mapped to the pathname.
*
* <p>Some containers may allow writing to the URL returned by
* this method using the methods of the URL class.
*
* <p>The resource content is returned directly, so be aware that
* requesting a <code>.jsp</code> page returns the JSP source code.
* Use a <code>RequestDispatcher</code> instead to include results of
* an execution.
*
* <p>This method has a different purpose than
* <code>java.lang.Class.getResource</code>,
* which looks up resources based on a class loader. This
* method does not use class loaders.
*
* @param path a <code>String</code> specifying
* the path to the resource
*
* @return the resource located at the named path,
* or <code>null</code> if there is no resource
* at that path
*
* @exception MalformedURLException if the pathname is not given in
* the correct form
*
*/
public URL getResource(String path) throws MalformedURLException;
/**
* Returns the resource located at the named path as
* an <code>InputStream</code> object.
*
* <p>The data in the <code>InputStream</code> can be
* of any type or length. The path must be specified according
* to the rules given in <code>getResource</code>.
* This method returns <code>null</code> if no resource exists at
* the specified path.
*
* <p>Meta-information such as content length and content type
* that is available via <code>getResource</code>
* method is lost when using this method.
*
* <p>The servlet container must implement the URL handlers
* and <code>URLConnection</code> objects necessary to access
* the resource.
*
* <p>This method is different from
* <code>java.lang.Class.getResourceAsStream</code>,
* 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.
*
*
* @param path a <code>String</code> specifying the path
* to the resource
*
* @return the <code>InputStream</code> returned to the
* servlet, or <code>null</code> if no resource
* exists at the specified path
*
*
*/
public InputStream getResourceAsStream(String path);
/**
*
* Returns a {@link RequestDispatcher} object that acts
* as a wrapper for the resource located at the given path.
* A <code>RequestDispatcher</code> 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.
*
* <p>The pathname must begin with a "/" and is interpreted as relative
* to the current context root. Use <code>getContext</code> to obtain
* a <code>RequestDispatcher</code> for resources in foreign contexts.
* This method returns <code>null</code> if the <code>ServletContext</code>
* cannot return a <code>RequestDispatcher</code>.
*
* @param path a <code>String</code> specifying the pathname
* to the resource
*
* @return a <code>RequestDispatcher</code> object
* that acts as a wrapper for the resource
* at the specified path, or <code>null</code> if
* the <code>ServletContext</code> cannot return
* a <code>RequestDispatcher</code>
*
* @see RequestDispatcher
* @see ServletContext#getContext
*
*/
public RequestDispatcher getRequestDispatcher(String path);
/**
* Returns a {@link RequestDispatcher} object that acts
* as a wrapper for the named servlet.
*
* <p>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
* {@link ServletConfig#getServletName}.
*
* <p>This method returns <code>null</code> if the
* <code>ServletContext</code>
* cannot return a <code>RequestDispatcher</code> for any reason.
*
* @param name a <code>String</code> specifying the name
* of a servlet to wrap
*
* @return a <code>RequestDispatcher</code> object
* that acts as a wrapper for the named servlet,
* or <code>null</code> if the <code>ServletContext</code>
* cannot return a <code>RequestDispatcher</code>
*
* @see RequestDispatcher
* @see ServletContext#getContext
* @see ServletConfig#getServletName
*
*/
public RequestDispatcher getNamedDispatcher(String name);
/**
*
* @deprecated As of Java Servlet API 2.1, with no direct replacement.
*
* <p>This method was originally defined to retrieve a servlet
* from a <code>ServletContext</code>. In this version, this method
* always returns <code>null</code> and remains only to preserve
* binary compatibility. This method will be permanently removed
* in a future version of the Java Servlet API.
*
* <p>In lieu of this method, servlets can share information using the
* <code>ServletContext</code> class and can perform shared business logic
* by invoking methods on common non-servlet classes.
*
*/
public Servlet getServlet(String name) throws ServletException;
/**
*
* @deprecated As of Java Servlet API 2.0, with no replacement.
*
* <p>This method was originally defined to return an <code>Enumeration</code>
* 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.
*
*/
public Enumeration getServlets();
/**
* @deprecated As of Java Servlet API 2.1, with no replacement.
*
* <p>This method was originally defined to return an
* <code>Enumeration</code>
* of all the servlet names known to this context. In this version,
* this method always returns an empty <code>Enumeration</code> and
* remains only to preserve binary compatibility. This method will
* be permanently removed in a future version of the Java Servlet API.
*
*/
public Enumeration getServletNames();
/**
*
* 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.
*
*
* @param msg a <code>String</code> specifying the
* message to be written to the log file
*
*/
public void log(String msg);
/**
* @deprecated As of Java Servlet API 2.1, use
* {@link #log(String message, Throwable throwable)}
* instead.
*
* <p>This method was originally defined to write an
* exception's stack trace and an explanatory error message
* to the servlet log file.
*
*/
public void log(Exception exception, String msg);
/**
* Writes an explanatory message and a stack trace
* for a given <code>Throwable</code> 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.
*
*
* @param message a <code>String</code> that
* describes the error or exception
*
* @param throwable the <code>Throwable</code> error
* or exception
*
*/
public void log(String message, Throwable throwable);
/**
* Returns a <code>String</code> 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..
*
* <p>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 <code>null</code>
* 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 <code>.war</code> archive).
*
*
* @param path a <code>String</code> specifying a virtual path
*
*
* @return a <code>String</code> specifying the real path,
* or null if the translation cannot be performed
*
*
*/
public String getRealPath(String path);
/**
* Returns the name and version of the servlet container on which
* the servlet is running.
*
* <p>The form of the returned string is
* <i>servername</i>/<i>versionnumber</i>.
* For example, the JavaServer Web Development Kit may return the string
* <code>JavaServer Web Dev Kit/1.0</code>.
*
* <p>The servlet container may return other optional information
* after the primary string in parentheses, for example,
* <code>JavaServer Web Dev Kit/1.0 (JDK 1.1.6; Windows NT 4.0 x86)</code>.
*
*
* @return a <code>String</code> containing at least the
* servlet container name and version number
*
*/
public String getServerInfo();
/**
* Returns a <code>String</code> containing the value of the named
* context-wide initialization parameter, or <code>null</code> if the
* parameter does not exist.
*
* <p>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.
*
* @param name a <code>String</code> containing the name of the
* parameter whose value is requested
*
* @return a <code>String</code> containing at least the
* servlet container name and version number
*
* @see ServletConfig#getInitParameter
*/
public String getInitParameter(String name);
/**
* Returns the names of the context's initialization parameters as an
* <code>Enumeration</code> of <code>String</code> objects, or an
* empty <code>Enumeration</code> if the context has no initialization
* parameters.
*
* @return an <code>Enumeration</code> of <code>String</code>
* objects containing the names of the context's
* initialization parameters
*
* @see ServletConfig#getInitParameter
*/
public Enumeration getInitParameterNames();
/**
* Returns the servlet container attribute with the given name,
* or <code>null</code> 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 using
* <code>getAttributeNames</code>.
*
* <p>The attribute is returned as a <code>java.lang.Object</code>
* or some subclass.
* Attribute names should follow the same convention as package
* names. The Java Servlet API specification reserves names
* matching <code>java.*</code>, <code>javax.*</code>,
* and <code>sun.*</code>.
*
*
* @param name a <code>String</code> specifying the name
* of the attribute
*
* @return an <code>Object</code> containing the value
* of the attribute, or <code>null</code>
* if no attribute exists matching the given
* name
*
* @see ServletContext#getAttributeNames
*
*/
public Object getAttribute(String name);
/**
* Returns an <code>Enumeration</code> containing the
* attribute names available
* within this servlet context. Use the
* {@link #getAttribute} method with an attribute name
* to get the value of an attribute.
*
* @return an <code>Enumeration</code> of attribute
* names
*
* @see #getAttribute
*
*/
public Enumeration getAttributeNames();
/**
*
* 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.
* <p>If listeners are configured on the <code>ServletContext</code> the
* container notifies them accordingly.
* <p>
* If a null value is passed, the effect is the same as calling
* <code>removeAttribute()</code>.
*
* <p>Attribute names should follow the same convention as package
* names. The Java Servlet API specification reserves names
* matching <code>java.*</code>, <code>javax.*</code>, and
* <code>sun.*</code>.
*
*
* @param name a <code>String</code> specifying the name
* of the attribute
*
* @param object an <code>Object</code> representing the
* attribute to be bound
*
*
*
*/
public void setAttribute(String name, Object object);
/**
* Removes the attribute with the given name from
* the servlet context. After removal, subsequent calls to
* {@link #getAttribute} to retrieve the attribute's value
* will return <code>null</code>.
* <p>If listeners are configured on the <code>ServletContext</code> the
* container notifies them accordingly.
*
*
* @param name a <code>String</code> specifying the name
* of the attribute to be removed
*
*/
public void removeAttribute(String name);
/**
* Returns the name of this web application corresponding to this ServletContext as specified in the deployment
* descriptor for this web application by the display-name element.
*
*
* @return The name of the web application or null if no name has been declared in the deployment descriptor.
* @since Servlet 2.3
*/
public String getServletContextName();
}
View Code
定义了 一些列的方法，具体就不看了，有兴趣的可以详细看下
Servlet 3.0+ 规范
我们采用4.0.1来看下源码
maven依赖
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>4.0.1</version>
<scope>provided</scope>
</dependency>
View Code
源码
/*
* Copyright (c) 1997-2018 Oracle and/or its affiliates. All rights reserved.
* Copyright 2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package javax.servlet;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.EnumSet;
import java.util.EventListener;
import java.util.Map;
import java.util.Set;
import javax.servlet.descriptor.JspConfigDescriptor;
/**
* Defines a set of methods that a servlet uses to communicate with its
* servlet container, for example, to get the MIME type of a file,
* dispatch requests, or write to a log file.
*
* There is one context per "web application" per Java Virtual Machine. (A
* "web application" is a collection of servlets and content installed under a
* specific subset of the server's URL namespace such as <code>/catalog</code>
* and possibly installed via a <code>.war</code> file.)
*
* <p>In the case of a web
* application marked "distributed" in its deployment descriptor, there will
* be one context instance for each virtual machine. In this situation, the
* context cannot be used as a location to share global information (because
* the information won't be truly global). Use an external resource like
* a database instead.
*
* <p>The <code>ServletContext</code> object is contained within
* the {@link ServletConfig} object, which the Web server provides the
* servlet when the servlet is initialized.
*
* @author Various
*
* @see Servlet#getServletConfig
* @see ServletConfig#getServletContext
*/
public interface ServletContext {
/**
* The name of the <tt>ServletContext</tt> attribute which stores
* the private temporary directory (of type <tt>java.io.File</tt>)
* provided by the servlet container for the <tt>ServletContext</tt>
*/
public static final String TEMPDIR = "javax.servlet.context.tempdir";
/**
* The name of the <code>ServletContext</code> attribute whose value
* (of type <code>java.util.List</code>) contains
* the list of names of JAR files in <code>WEB-INF/lib</code> ordered by
* their web fragment names (with possible exclusions if
* <code></code> without any
* <code></code> related configuration
* that was aggregated from the <code>web.xml</code> and
* <code>web-fragment.xml</code> descriptor files of the web application
* represented by this ServletContext.
*
* @return the <code></code> related configuration
* that was aggregated from the <code>web.xml</code> and
* <code>web-fragment.xml</code> descriptor files of the web application
* represented by this ServletContext, or null if no such configuration
* exists
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @see javax.servlet.descriptor.JspConfigDescriptor
*
* @since Servlet 3.0
*/
public JspConfigDescriptor getJspConfigDescriptor();
/**
* Gets the class loader of the web application represented by this
* ServletContext.
*
* <p>If a security manager exists, and the caller's class loader
* is not the same as, or an ancestor of the requested class loader,
* then the security manager's <code>checkPermission</code> method is
* called with a <code>RuntimePermission("getClassLoader")</code>
* permission to check whether access to the requested class loader
* should be granted.
*
* @return the class loader of the web application represented by this
* ServletContext
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @throws SecurityException if a security manager denies access to
* the requested class loader
*
* @since Servlet 3.0
*/
public ClassLoader getClassLoader();
/**
* Declares role names that are tested using <code>isUserInRole</code>.
*
* <p>Roles that are implicitly declared as a result of their use within
* the {@link ServletRegistration.Dynamic#setServletSecurity
* setServletSecurity} or {@link ServletRegistration.Dynamic#setRunAsRole
* setRunAsRole} methods of the {@link ServletRegistration} interface need
* not be declared.
*
* @param roleNames the role names being declared
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @throws IllegalArgumentException if any of the argument roleNames is
* null or the empty string
*
* @throws IllegalStateException if the ServletContext has already
* been initialized
*
* @since Servlet 3.0
*/
public void declareRoles(String... roleNames);
/**
* Returns the configuration name of the logical host on which the
* ServletContext is deployed.
*
* Servlet containers may support multiple logical hosts. This method must
* return the same name for all the servlet contexts deployed on a logical
* host, and the name returned by this method must be distinct, stable per
* logical host, and suitable for use in associating server configuration
* information with the logical host. The returned value is NOT expected
* or required to be equivalent to a network address or hostname of the
* logical host.
*
* @return a <code>String</code> containing the configuration name of the
* logical host on which the servlet context is deployed.
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @since Servlet 3.1
*/
public String getVirtualServerName();
/**
* Gets the session timeout in minutes that are supported by default for
* this <tt>ServletContext</tt>.
*
* @return the session timeout in minutes that are supported by default for
* this <tt>ServletContext</tt>
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @since Servlet 4.0
*/
public int getSessionTimeout();
/**
* Sets the session timeout in minutes for this ServletContext.
*
* @param sessionTimeout session timeout in minutes
*
* @throws IllegalStateException if this ServletContext has already
* been initialized
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @since Servlet 4.0
*/
public void setSessionTimeout(int sessionTimeout);
/**
* Gets the request character encoding that are supported by default for
* this <tt>ServletContext</tt>. This method returns null if no request
* encoding character encoding has been specified in deployment descriptor
* or container specific configuration (for all web applications in the
* container).
*
* @return the request character encoding that are supported by default for
* this <tt>ServletContext</tt>
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @since Servlet 4.0
*/
public String getRequestCharacterEncoding();
/**
* Sets the request character encoding for this ServletContext.
*
* @param encoding request character encoding
*
* @throws IllegalStateException if this ServletContext has already
* been initialized
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @since Servlet 4.0
*/
public void setRequestCharacterEncoding(String encoding);
/**
* Gets the response character encoding that are supported by default for
* this <tt>ServletContext</tt>. This method returns null if no response
* encoding character encoding has been specified in deployment descriptor
* or container specific configuration (for all web applications in the
* container).
*
* @return the request character encoding that are supported by default for
* this <tt>ServletContext</tt>
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @since Servlet 4.0
*/
public String getResponseCharacterEncoding();
/**
* Sets the response character encoding for this ServletContext.
*
* @param encoding response character encoding
*
* @throws IllegalStateException if this ServletContext has already
* been initialized
*
* @throws UnsupportedOperationException if this ServletContext was
* passed to the {@link ServletContextListener#contextInitialized} method
* of a {@link ServletContextListener} that was neither declared in
* <code>web.xml</code> or <code>web-fragment.xml</code>, nor annotated
* with {@link javax.servlet.annotation.WebListener}
*
* @since Servlet 4.0
*/
public void setResponseCharacterEncoding(String encoding);
}
View Code
从3.0新增的方法，方法描述上都有标明@since Servlet 3.0，大家可以去细看下3.0具体新增了哪些方法。新增的add系列方法如下
也就是说可以通过ServletContext向servlet容器添加Filter、Listener和Servlet了。
补充
3.0之前和3.0之后，maven依赖的artifactId是不同的，大家需要注意一下；
servlet 3.0是一个大的版本变动，相比之前增加了比较多的特性，本文就涉及到其中一个特性：支持无web.xml配置（新的注解支持）
servlet 3.0及之后，Filter、Servlet和Listener支持注解配置（3.0之前都是配置在web.xml中）
Filter注册
springboot实现
实现Filter接口实现我们自己的Filter，这个与web.xml时期一样
package com.lee.register.filter;
import javax.servlet.*;
import java.io.IOException;
public class MyFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("myfilter init...");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("过滤处理");
chain.doFilter(request, response);
}
@Override
public void destroy() {
System.out.println("myfilter destroy...");
}
}
View Code
利用FilterRegistrationBean将我们自定义的Filter注册到容器
package com.lee.register.config;
import com.lee.register.filter.MyFilter;
import com.lee.register.listener.MyListener;
import com.lee.register.servlet.MyServlet;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import java.util.Arrays;
@Configuration
public class MyConfig {
@Bean
public ServletListenerRegistrationBean myListener() {
ServletListenerRegistrationBean registrationBean = new ServletListenerRegistrationBean(new MyListener());
return registrationBean;
}
@Bean
public FilterRegistrationBean myFilter() {
FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(new MyFilter());
filterRegistrationBean.setUrlPatterns(Arrays.asList("/hello","/myServlet"));
return filterRegistrationBean;
}
@Bean
public ServletRegistrationBean myServlet() {
ServletRegistrationBean registrationBean = new ServletRegistrationBean(new MyServlet());
registrationBean.setUrlMappings(Arrays.asList("/myServlet"));
registrationBean.setLoadOnStartup(1);
return registrationBean;
}
}
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工程详情请点：spring-boot-filter；FilterRegistrationBean的作用与在web.xml中配置Filter类似，只是底层用了servlet3.0的新特性
源码分析
我们知道servlet3.0+，可以通过ServeltContext来注册Filter（当然还包括Servlet、Listener）到Servlet容器；至于注册到Servlet容器后，容器容器如何处理Filter就不是本文的范畴了。我们姑且这样认为：通过ServletContext注册Filter到容器，那么Filter就能起到过滤作用了。那么问题来了，springboot是如何将Filter注册到容器的？
FilterRegistrationBean的源码
/*
* Copyright 2012-2017 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.boot.web.servlet;
import javax.servlet.Filter;
import javax.servlet.ServletContext;
import org.springframework.util.Assert;
/**
* A {@link ServletContextInitializer} to register {@link Filter}s in a Servlet 3.0+
* container. Similar to the {@link ServletContext#addFilter(String, Filter) registration}
* features provided by {@link ServletContext} but with a Spring Bean friendly design.
* <p>
* The {@link #setFilter(Filter) Filter} must be specified before calling
* {@link #onStartup(ServletContext)}. Registrations can be associated with
* {@link #setUrlPatterns URL patterns} and/or servlets (either by {@link #setServletNames
* name} or via a {@link #setServletRegistrationBeans ServletRegistrationBean}s. When no
* URL pattern or servlets are specified the filter will be associated to '/*'. The filter
* name will be deduced if not specified.
*
* @param <T> the type of {@link Filter} to register
* @author Phillip Webb
* @since 1.4.0
* @see ServletContextInitializer
* @see ServletContext#addFilter(String, Filter)
* @see DelegatingFilterProxyRegistrationBean
*/
public class FilterRegistrationBean<T extends Filter>
extends AbstractFilterRegistrationBean<T> {
/**
* Filters that wrap the servlet request should be ordered less than or equal to this.
*/
public static final int REQUEST_WRAPPER_FILTER_MAX_ORDER = AbstractFilterRegistrationBean.REQUEST_WRAPPER_FILTER_MAX_ORDER;
private T filter;
/**
* Create a new {@link FilterRegistrationBean} instance.
*/
public FilterRegistrationBean() {
}
/**
* Create a new {@link FilterRegistrationBean} instance to be registered with the
* specified {@link ServletRegistrationBean}s.
* @param filter the filter to register
* @param servletRegistrationBeans associate {@link ServletRegistrationBean}s
*/
public FilterRegistrationBean(T filter,
ServletRegistrationBean<?>... servletRegistrationBeans) {
super(servletRegistrationBeans);
Assert.notNull(filter, "Filter must not be null");
this.filter = filter;
}
@Override
public T getFilter() {
return this.filter;
}
/**
* Set the filter to be registered.
* @param filter the filter
*/
public void setFilter(T filter) {
Assert.notNull(filter, "Filter must not be null");
this.filter = filter;
}
}
View Code
FilterRegistrationBean的类描述：一个用于向Servlet 3.0+容器注册Filter的ServletContextInitializer，类似于ServletContext提供的ServletContext＃addFilter（String，Filter）注册功能，但具有Spring Bean特性的友好设计。相当于对ServletContext＃addFilter进行了spring bean的友好性适配，本质还是ServletContext＃addFilter。
FilterRegistrationBean的类继承图
我们来看看ServletContextInitializer，感觉和ServeltContext有很大的关系，源码如下
/*
* Copyright 2012-2017 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.boot.web.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import org.springframework.web.SpringServletContainerInitializer;
import org.springframework.web.WebApplicationInitializer;
/**
* Interface used to configure a Servlet 3.0+ {@link ServletContext context}
* programmatically. Unlike {@link WebApplicationInitializer}, classes that implement this
* interface (and do not implement {@link WebApplicationInitializer}) will <b>not</b> be
* detected by {@link SpringServletContainerInitializer} and hence will not be
* automatically bootstrapped by the Servlet container.
* <p>
* This interface is primarily designed to allow {@link ServletContextInitializer}s to be
* managed by Spring and not the Servlet container.
* <p>
* For configuration examples see {@link WebApplicationInitializer}.
*
* @author Phillip Webb
* @since 1.4.0
* @see WebApplicationInitializer
*/
@FunctionalInterface
public interface ServletContextInitializer {
/**
* Configure the given {@link ServletContext} with any servlets, filters, listeners
* context-params and attributes necessary for initialization.
* @param servletContext the {@code ServletContext} to initialize
* @throws ServletException if any call against the given {@code ServletContext}
* throws a {@code ServletException}
*/
void onStartup(ServletContext servletContext) throws ServletException;
}
View Code
ServletContextInitializer允许我们以编程方式配置Servlet 3.0+ ServletContext上下文，并且SpringServletContainerInitializer不会检测到实现此接口的类（类没有实现WebApplicationInitializer），因此不会被Servlet容器自动引导；ServletContextInitializer的设计目的是由spring管理，而不是Servlet容器。ServletContextInitializer就一个方法：onStartup，我们顺着FilterRegistrationBean的类图来看看onStartup的实现
我们发现，最终还是调用ServletContext的addFilter方法将Filter注册到Servlet容器。问题又来了，ServletContextInitializer的onStartup又是在哪里被调用的呢？
springboot的启动过程中肯定在哪个地方对ServletContextInitializer的onStartup进行了调用，我们接着往下看，我们从ServletWebServerApplicationContext.java的createWebServer方法开始（Springboot启动开始到createWebServer的过程就省了）
先去spring的beanFactory中获取ServletContextInitializer的全部实例，并将其放入到ServletContextInitializerBeans的initializers中，然后遍历initializers，调用每个ServletContextInitializer的onStartup方法（有人感觉这里有点多余，其实你把initializers想成缓存就好理解了，肯定还有其他地方会用到initializers）。
至此也就通了，spring将@Bean修饰的RegistrationBean注册到beanFactory，然后从beanFactory中获取全部的ServletContextInitializer，遍历它们并调用他们的onStartup方法将RegistrationBean中的bean注册到servlet容器；但是有一点@Bean注解是如何将bean注册到beanFactory的本文没有涉及，会放到springboot启动系列篇中，敬请期待。
总结
1、ServletContext是request与response交互的平台，也是我们的web应用与servlet容器沟通的桥梁；就从本文来说，Filter、Servlet、Listener的注册都是通过ServletContext来实现的
2、Servlet3.0+有很多新特性，包括Filter、Servlet、Listener的注册，不再只是通过web.xml实现了。而springboot也只是对ServletContext的add系列方法进行了拓展，使得具有spring的友好性，而FilterRegistrationBean就是具体的实现之一。
3、springboot启动过程中，调用ServletContextInitializer类型的实例的onStartup方法，完成指定bean到servlet容器的注册；指定bean就是指我们自定义的Filter、Servlet、Listener，而不是RegistrationBean类型的实例。
参考
《深入分析Java Web技术内幕》
