1.1 ServletConfig的概述
Servlet容器初始化一个servlet对象时，会为这个servlet对象创建一个servletConfig对象。在servletConfig对象中包含了servlet的初始化参数信息。此外，servletConfig对象还与servletContext对象关联。Servlet容器在调用servlet对象的init(ServletConfig config)方法时，会把servletConfig对象当做参数传递给servlet对象。Init(ServletConfig config)方法会使得当前servlet对象与servletConfig对象建立关联关系。
简单的说就是：servlet 容器使用的 servlet 配置对象，该对象在初始化期间将信息传递给 servlet。
1.1.1 ServletConfig的方法
| 方法 | 描述 |
|---|---|
| String getInitParameter(String name) | Returns a String containing the value of the named initialization parameter, or null if the parameter does not exist. |
| Enumeration getInitParameterNames() | Returns the names of the servlet's initialization parameters as an Enumeration of String objects, or an empty Enumeration if the servlet has no initialization parameters. |
| ServletContext getServletContext() | Returns a reference to the ServletContext in which the caller is executing. |
| String getServletName() | Returns the name of this servlet instance. |
1.1.2 ServletConfig的入门案例
xml文件加入的内容
Demo5Servlet
Demo5Servlet
com.itheima.servlet.Demo5Servlet
username
zhangsan
password
123456
注意
程序代码
public class Demo5Servlet extends HttpServlet {
/*private ServletConfig config;
@Override
public void init(ServletConfig config) throws ServletException {
this.config = config;
}*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
ServletConfig config = getServletConfig();
//根据初始化参数的name来获取value
String username = config.getInitParameter("username");
String password = config.getInitParameter("password");
System.out.println(username);
System.out.println(password);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
- 在实际的作用有
- 获取字符集编码 UTF-8
- 获取数据库连接信息 用户名 密码 url
- 获取配置文件
1.2 ServletContext的概述
ServletContext是servlet与servlet容器之间的直接通信的接口。Servlet容器在启动一个Web应用时，会为它创建一个servletContext对象。每个web应用有唯一的servletContext对象。同一个web应用的所有servlet对象共享一个serveltContext,servlet对象可以通过它来访问容器中的各种资源。
上下文对象, 他是在服务器启动的时候,会为每个web项目创建一个单独的servletContext对象,他代表了当前的WEB应用
1.2.1 ServletContext的部分方法
| 方法 | 描述 |
|---|---|
| Object getAttribute(String name) | Returns the servlet container attribute with the given name, or null if there is no attribute by that name. |
| Enumeration getAttributeNames() | Returns an Enumeration containing the attribute names available within this servlet context. |
| ServletContext getContext(String uripath) | Returns a ServletContext object that corresponds to a specified URL on the server. |
| String getContextPath() | Returns the context path of the web application. |
| String getInitParameter(String name) | Returns a String containing the value of the named context-wide initialization parameter, or null if the parameter does not exist. |
| Enumeration getInitParameterNames() | Returns the names of the context's initialization parameters as an Enumeration of String objects, or an empty Enumeration if the context has no initialization parameters. |
| Servlet getServlet(String name) | Deprecated. As of Java Servlet API 2.1, with no direct replacement. |
| String getServletContextName() | 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. |
| void log(String msg) | Writes the specified message to a servlet log file, usually an event log. |
| void removeAttribute(String name) | Removes the attribute with the given name from the servlet context. |
| void setAttribute(String name, Object object) | Binds an object to a given attribute name in this servlet context. |
1.2.2 ServletContext代码功能演示
- 获取Context对象
public class ContextDemo extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获取ServletContext对象
//通过ServletConfig对象来获取
//ServletContext context = getServletConfig().getServletContext();
//同过Servlet的方法来获取
ServletContext context = getServletContext();
//根据name来获取value
String username = context.getInitParameter("username");
String password = context.getInitParameter("password");
System.out.println(username);
System.out.println(password);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
- 获取属性值
public class ContextDemo2 extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获取ServletContext对象
ServletContext context = getServletContext();
//设置数据
context.setAttribute("username", "zhangsan");
context.setAttribute("username", "lisi");
//获取数据
Object obj = context.getAttribute("username");
response.getWriter().println(obj);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
- 获取路径
public class ContextDemo4 extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.getWriter().println("itcast");
//获取ServletContext对象
ServletContext context = getServletContext();
//获取当前WEB应用的绝对路径
//String path = context.getRealPath("/WEB-INF");
//System.out.println(path);
RequestDispatcher rd = context.getRequestDispatcher("/ContextDemo2");
//转发
//rd.forward(request, response);
//包含
rd.include(request, response);
response.getWriter().println("itheima");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
1.3 ServletConfig与ServletContext的区别
这里推荐其他程序员的一篇博客 写的很棒
跳转地址 《ServletConfig和ServletContext的区别及应用》