Servlet ServletConfig配置信息
ServletConfig
對象是由每個servlet的Web容器創建的。這個對象可用於從web.xml
文件獲取配置信息。
如果從web.xml
文件修改配置信息,就不需要更改servlet中的代碼。因此,對於有特定配置內容需要不定時修改,這樣會更容易管理Web應用程序。
ServletConfig的優點
ServletConfig
的核心優點是,如果可以修改web.xml
文件中的信息,則不需要編輯servlet代碼文件。
ServletConfig接口的方法
編號
方法
描述
1
public String getInitParameter(String name)
返回指定參數名稱的參數值。
2
public Enumeration getInitParameterNames()
返回所有初始化參數名稱的枚舉。
3
public String getServletName()
返回servlet的名稱。
4
public ServletContext getServletContext()
返回ServletContext
的對象。
如何獲取ServletConfig的對象?
- 可通過調用Servlet接口的
getServletConfig()
方法來返回ServletConfig
對象。
getServletConfig()方法的語法
public ServletConfig getServletConfig();
getServletConfig()方法的示例
ServletConfig config=getServletConfig();
//Now we can call the methods of ServletConfig interface
爲servlet提供初始化參數的語法
servlet的init-param
子元素用於指定servlet的初始化參數。
<web-app>
<servlet>
......
<init-param>
<param-name>parameter_name</param-name>
<param-value>parameter_value</param-value>
</init-param>
......
</servlet>
</web-app>
獲取初始化參數的ServletConfig示例
在這個例子中,將從web.xml
文件獲取一個初始化參數,並在servlet中打印這些信息。
創建一個名稱爲:ServletConfig的動態Web應用項目,其結構如下所示 -
下面是幾個主要的代碼文件 -
文件:ConfigServlet.java -
package com.yiibai;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class ConfigServlet
*/
public class ConfigServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("text/html");
PrintWriter out = response.getWriter();
ServletConfig config = getServletConfig();
String driver = config.getInitParameter("mysql_driver");
out.print("Driver details is: <b>" + driver+"</b>");
out.close();
}
}
文件:web.xml -
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="WebApp_ID" version="3.1">
<display-name>ConfigServlet</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>ConfigServlet</servlet-name>
<servlet-class>com.yiibai.ConfigServlet</servlet-class>
<init-param>
<param-name>mysql_driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>ConfigServlet</servlet-name>
<url-pattern>/dbconfig</url-pattern>
</servlet-mapping>
</web-app>
將上面項目部署並訪問URL: http://localhost:8080/ConfigServlet/dbconfig ,如果程序沒有問題,那麼應該會看到以下結果 -
獲取所有初始化參數的ServletConfig示例
在這個例子中,我們從web.xml
文件獲取所有的初始化參數,並在servlet中打印這些信息。
幾個主要代碼文件如下 -
文件:ConfigServletAll.java -
package com.yiibai;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class ConfigServletAll
*/
public class ConfigServletAll extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
response.setContentType("text/html");
PrintWriter out = response.getWriter();
ServletConfig config = getServletConfig();
Enumeration<String> e = config.getInitParameterNames();
String str = "";
while (e.hasMoreElements()) {
str = e.nextElement();
out.print("Name: " + str);
out.print(" value: " + config.getInitParameter(str)+"<br/>");
}
out.close();
}
}
文件:web.xml -
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="WebApp_ID" version="3.1">
<display-name>ConfigServlet</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>ConfigServlet</servlet-name>
<servlet-class>com.yiibai.ConfigServlet</servlet-class>
<init-param>
<param-name>mysql_driver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>ConfigServlet</servlet-name>
<url-pattern>/dbconfig</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>ConfigServletAll</servlet-name>
<servlet-class>com.yiibai.ConfigServletAll</servlet-class>
<init-param>
<param-name>mssql_driver</param-name>
<param-value>com.mssql.jdbc.Driver</param-value>
</init-param>
<init-param>
<param-name>username</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>passwd</param-name>
<param-value>123456</param-value>
</init-param>
</servlet>
<servlet-mapping>
<servlet-name>ConfigServletAll</servlet-name>
<url-pattern>/dbconfigall</url-pattern>
</servlet-mapping>
</web-app>
將上面項目部署並訪問URL: http://localhost:8080/ConfigServlet/dbconfigall ,如果程序沒有問題,那麼應該會看到以下結果 -