本帖最后由 大山哥哥 于 2018-2-1 19:34 编辑
Servlet中的四大域对象
1.ServletContext域对象
2.Seesion域对象
3.Request域对象
4.PageContext域对象
ServletContext是一个域对象.
* 作用范围:整个web工程.
* 创建:服务器启动的时候,tomcat服务器为每个web项目创建一个单独ServletContext对象.
* 销毁:服务器关闭的时候,或者项目从服务器中移除的时候.
ServletContext的作用:
1.作为域对象来存取数据
2.用来读取web项目下文件
3.初始化全局参数
4.用来获得文件的MIME类型
1. ServletContext作为域对象存取数据
方法:
1.设置全局属性的值
void setAttribute(String name, Object object);
2.获取相应属性的值
Object getAttribute(String name);
[Java] 纯文本查看 复制代码 public class HttpServletContextDemo extends HttpServlet{
private static final long serialVersionUID = -7168725846977975610L;
@Override
public void init() throws ServletException {
int count = 0;
//----------------------------------------------------
//设置全局参数count
this.getServletContext().setAttribute("count", count);
//----------------------------------------------------
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//中文乱码
resp.setContentType("text/html;charset=UTF-8");
//----------------------------------------------------
//获取全局参数count
int count = (int) this.getServletContext().getAttribute("count");
//----------------------------------------------------
count++;
this.getServletContext().setAttribute("count", count);
resp.getWriter().println("您是第"+count+"个访问者");
}
}
2. ServletContext读取项目下文件
方法:
1.根据提供路径读取文件返回一个文件的输入流.
InputStream is = getResourceAsStream(String path);
2.返回一个文件的磁盘绝对路径
String path = getRealPath(String path);
[Java] 纯文本查看 复制代码 public class HttpServletContextDemo extends HttpServlet{
private static final long serialVersionUID = -7168725846977975610L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//中文乱码
resp.setContentType("text/html;charset=UTF-8");
ServletContext context = this.getServletContext();
//----------------------------------------------------
//读取配置文件
InputStream is = context.getResourceAsStream("WEB-INF/classes/db.properties");
//----------------------------------------------------
Properties p = new Properties();
p.load(is);
System.out.println(p);
//----------------------------------------------------
//获取配置文件所在得绝对路径
String path = context.getRealPath("WEB-INF/classes/db.properties");
//----------------------------------------------------
System.out.println(path);
}
}
3. ServletContext初始化全局参数
方法:
1.获取全局初始化参数的值
String getInitParameter(String name);
2.获取全局所有初始化参数的名字组成的枚举
Enumeration getInitParameterNames();
[Java] 纯文本查看 复制代码 public class HttpServletContextDemo extends HttpServlet{
private static final long serialVersionUID = -7168725846977975610L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//中文乱码
resp.setContentType("text/html;charset=UTF-8");
ServletContext context = getServletContext();
//----------------------------------------------------
//获取全局指定初始化参数
String user = context.getInitParameter("user");
System.out.println(user);
//----------------------------------------------------
//----------------------------------------------------
//获取全局所有初始化参数
Enumeration enumration = context.getInitParameterNames();
while(enumration.hasMoreElements()){
String name = (String) enumration.nextElement();
String value = context.getInitParameter(name);
System.out.println(name+":"+value);
}
//----------------------------------------------------
}
}
在web.xml中配置全局参数
[XML] 纯文本查看 复制代码 <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee [url=http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd]http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd[/url]"
id="WebApp_ID" version="2.5">
<display-name>ServletDemo</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
---------------------------------------------------
<context-param>
<param-name>user</param-name>
<param-value>b3a4a</param-value>
</context-param>
<context-param>
<param-name>pass</param-name>
<param-value>123456</param-value>
</context-param>
---------------------------------------------------
<!-- ServletContext演示 -->
<servlet>
<servlet-name>HttpServletContextDemo</servlet-name>
<servlet-class>com.b3a4a.servlet.HttpServletContextDemo</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HttpServletContextDemo</servlet-name>
<url-pattern>/servletContext</url-pattern>
</servlet-mapping>
</web-app>
4. ServletContext用来获得文件的MIME类型
方法:
1.获取文件的MimeType类型
String getMimeType(String path);
[Java] 纯文本查看 复制代码
public class HttpServletContextDemo extends HttpServlet{
private static final long serialVersionUID = -7168725846977975610L;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//中文乱码
resp.setContentType("text/html;charset=UTF-8");
//----------------------------------------------------
//获取文件的MimeType类型
String mimeType = this.getServletContext().getMimeType("html/success.html");
System.out.println(mimeType);
//----------------------------------------------------
}
}
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