javawebServletConfig解学习总结二.docx

javaweb学习总结(六)Servlet开发(二)一、ServletConfig讲解1.1、配置Servlet初始化参数在Servlet的配置文件web.xml中，可以使用一个或多个标签为servlet配置一些初始化参数。例如： 1 2 ServletConfigDemo1 3 gacl.servlet.study.ServletConfigDemo1 4 5 6 name 7 gacl 8 9 10 password11 12312 13 14 charset15 UTF-816 17 1.2、通过ServletConfig获取Servlet的初始化参数当servlet配置了初始化参数后，web容器在创建servlet实例对象时，会自动将这些初始化参数封装到ServletConfig对象中，并在调用servlet的init方法时，将ServletConfig对象传递给servlet。进而，我们通过ServletConfig对象就可以得到当前servlet的初始化参数信息。例如： 1 package gacl.servlet.study; 2 3 import java.io.IOException; 4 import java.util.Enumeration; 5 import javax.servlet.ServletConfig; 6 import javax.servlet.ServletException; 7 import javax.servlet.http.HttpServlet; 8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse;10 11 public class ServletConfigDemo1 extends HttpServlet 12 13 /*14 * 定义ServletConfig对象来接收配置的初始化参数15 */16 private ServletConfig config;17 18 /*19 * 当servlet配置了初始化参数后，web容器在创建servlet实例对象时，20 * 会自动将这些初始化参数封装到ServletConfig对象中，并在调用servlet的init方法时，21 * 将ServletConfig对象传递给servlet。进而，程序员通过ServletConfig对象就可以22 * 得到当前servlet的初始化参数信息。23 */24 Override25 public void init(ServletConfig config) throws ServletException 26 this.config = config;27 28 29 public void doGet(HttpServletRequest request, HttpServletResponse response)30 throws ServletException, IOException 31 /获取在web.xml中配置的初始化参数32 String paramVal = this.config.getInitParameter(name);/获取指定的初始化参数33 response.getWriter().print(paramVal);34 35 response.getWriter().print();36 /获取所有的初始化参数37 Enumeration e = config.getInitParameterNames();38 while(e.hasMoreElements()39 String name = e.nextElement();40 String value = config.getInitParameter(name);41 response.getWriter().print(name + = + value + );42 43 44 45 public void doPost(HttpServletRequest request, HttpServletResponse response)46 throws ServletException, IOException 47 this.doGet(request, response);48 49 50 运行结果如下：二、ServletContext对象WEB容器在启动时，它会为每个WEB应用程序都创建一个对应的ServletContext对象，它代表当前web应用。ServletConfig对象中维护了ServletContext对象的引用，开发人员在编写servlet时，可以通过ServletConfig.getServletContext方法获得ServletContext对象。由于一个WEB应用中的所有Servlet共享同一个ServletContext对象，因此Servlet对象之间可以通过ServletContext对象来实现通讯。ServletContext对象通常也被称之为context域对象。三、ServletContext的应用3.1、多个Servlet通过ServletContext对象实现数据共享范例：ServletContextDemo1和ServletContextDemo2通过ServletContext对象实现数据共享 1 package gacl.servlet.study; 2 3 import java.io.IOException; 4 import javax.servlet.ServletContext; 5 import javax.servlet.ServletException; 6 import javax.servlet.http.HttpServlet; 7 import javax.servlet.http.HttpServletRequest; 8 import javax.servlet.http.HttpServletResponse; 9 10 public class ServletContextDemo1 extends HttpServlet 11 12 public void doGet(HttpServletRequest request, HttpServletResponse response)13 throws ServletException, IOException 14 String data = xdp_gacl;15 /*16 * ServletConfig对象中维护了ServletContext对象的引用，开发人员在编写servlet时，17 * 可以通过ServletConfig.getServletContext方法获得ServletContext对象。18 */19 ServletContext context = this.getServletConfig().getServletContext();/获得ServletContext对象20 context.setAttribute(data, data); /将data存储到ServletContext对象中21 22 23 public void doPost(HttpServletRequest request, HttpServletResponse response)24 throws ServletException, IOException 25 doGet(request, response);26 27 1 package gacl.servlet.study; 2 3 import java.io.IOException; 4 import javax.servlet.ServletContext; 5 import javax.servlet.ServletException; 6 import javax.servlet.http.HttpServlet; 7 import javax.servlet.http.HttpServletRequest; 8 import javax.servlet.http.HttpServletResponse; 9 10 public class ServletContextDemo2 extends HttpServlet 11 12 public void doGet(HttpServletRequest request, HttpServletResponse response)13 throws ServletException, IOException 14 ServletContext context = this.getServletContext();15 String data = (String) context.getAttribute(data);/从ServletContext对象中取出数据16 response.getWriter().print(data=+data);17 18 19 public void doPost(HttpServletRequest request, HttpServletResponse response)20 throws ServletException, IOException 21 doGet(request, response);22 23 先运行ServletContextDemo1，将数据data存储到ServletContext对象中，然后运行ServletContextDemo2就可以从ServletContext对象中取出数据了，这样就实现了数据共享，如下图所示：3.2、获取WEB应用的初始化参数在web.xml文件中使用标签配置WEB应用的初始化参数，如下所示： 1 2 4 5 6 7 url 8 jdbc:mysql:/localhost:3306/test 9 10 11 12 index.jsp13 14 获取Web应用的初始化参数，代码如下： 1 package gacl.servlet.study; 2 3 import java.io.IOException; 4 import javax.servlet.ServletContext; 5 import javax.servlet.ServletException; 6 import javax.servlet.http.HttpServlet; 7 import javax.servlet.http.HttpServletRequest; 8 import javax.servlet.http.HttpServletResponse; 9 10 11 public class ServletContextDemo3 extends HttpServlet 12 13 public void doGet(HttpServletRequest request, HttpServletResponse response)14 throws ServletException, IOException 15 16 ServletContext context = this.getServletContext();17 /获取整个web站点的初始化参数18 String contextInitParam = context.getInitParameter(url);19 response.getWriter().print(contextInitParam);20 21 22 public void doPost(HttpServletRequest request, HttpServletResponse response)23 throws ServletException, IOException 24 doGet(request, response);25 26 27 运行结果：3.3、用servletContext实现请求转发ServletContextDemo4 1 package gacl.servlet.study; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 import javax.servlet.RequestDispatcher; 6 import javax.servlet.ServletContext; 7 import javax.servlet.ServletException; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest;10 import javax.servlet.http.HttpServletResponse;11 12 public class ServletContextDemo4 extends HttpServlet 13 14 public void doGet(HttpServletRequest request, HttpServletResponse response)15 throws ServletException, IOException 16 String data = abcdefghjkl;17 response.getOutputStream().write(data.getBytes();18 ServletContext context = this.getServletContext();/获取ServletContext对象19 RequestDispatcher rd = context.getRequestDispatcher(/servlet/ServletContextDemo5);/获取请求转发对象(RequestDispatcher)20 rd.forward(request, response);/调用forward方法实现请求转发21 22 23 public void doPost(HttpServletRequest request, HttpServletResponse response)24 throws ServletException, IOException 25 26 ServletContextDemo5 1 package gacl.servlet.study; 2 3 import java.io.IOException; 4 import javax.servlet.ServletException; 5 import javax.servlet.http.HttpServlet; 6 import javax.servlet.http.HttpServletRequest; 7 import javax.servlet.http.HttpServletResponse; 8 9 public class ServletContextDemo5 extends HttpServlet 10 11 public void doGet(HttpServletRequest request, HttpServletResponse response)12 throws ServletException, IOException 13 response.getOutputStream().write(servletDemo5.getBytes();14 15 16 public void doPost(HttpServletRequest request, HttpServletResponse response)17 throws ServletException, IOException 18 this.doGet(request, response);19 20 21 运行结果：访问的是ServletContextDemo4，浏览器显示的却是ServletContextDemo5的内容，这就是使用ServletContext实现了请求转发3.4、利用ServletContext对象读取资源文件项目目录结构如下：代码范例：使用servletContext读取资源文件 1 package gacl.servlet.study; 2 3 import java.io.FileInputStream; 4 import java.io.FileNotFoundException; 5 import java.io.IOException; 6 import java.io.InputStream; 7 import java.text.MessageFormat; 8 import java.util.Properties; 9 import javax.servlet.ServletException; 10 import javax.servlet.http.HttpServlet; 11 import javax.servlet.http.HttpServletRequest; 12 import javax.servlet.http.HttpServletResponse; 13 14 /* 15 * 使用servletContext读取资源文件 16 * 17 * author gacl 18 * 19 */ 20 public class ServletContextDemo6 extends HttpServlet 21 22 public void doGet(HttpServletRequest request, HttpServletResponse response) 23 throws ServletException, IOException 24 /* 25 * response.setContentType(text/html;charset=UTF-8);目的是控制浏览器用UTF-8进行解码； 26 * 这样就不会出现中文乱码了 27 */ 28 response.setHeader(content-type,text/html;charset=UTF-8); 29 readSrcDirPropCfgFile(response);/读取src目录下的properties配置文件 30 response.getWriter().println(); 31 readWebRootDirPropCfgFile(response);/读取WebRoot目录下的properties配置文件 32 response.getWriter().println(); 33 readPropCfgFile(response);/读取src目录下的db.config包中的perties配置文件 34 response.getWriter().println(); 35 readPropCfgFile2(response);/读取src目录下的gacl.servlet.study包中的perties配置文件 36 37 38 39 /* 40 * 读取src目录下的gacl.servlet.study包中的perties配置文件 41 * param response 42 * throws IOException 43 */ 44 private void readPropCfgFile2(HttpServletResponse response) 45 throws IOException 46 InputStream in = this.getServletContext().getResourceAsStream(/WEB-INF/classes/gacl/servlet/study/perties); 47 Properties prop = new Properties(); 48 prop.load(in); 49 String driver = prop.getProperty(driver); 50 String url = prop.getProperty(url); 51 String username = prop.getProperty(username); 52 String password = prop.getProperty(password); 53 response.getWriter().println(读取src目录下的gacl.servlet.study包中的perties配置文件：); 54 response.getWriter().println( 55 MessageFormat.format( 56 driver=0,url=1,username=2,password=3, 57 driver,url, username, password); 58 59 60 /* 61 * 读取src目录下的db.config包中的perties配置文件 62 * param response 63 * throws FileNotFoundException 64 * throws IOException 65 */ 66 private void readPropCfgFile(HttpServletResponse response) 67 throws FileNotFoundException, IOException 68 /通过ServletContext获取web资源的绝对路径 69 String path = this.getServletContext().getRealPath(/WEB-INF/classes/db/config/perties); 70 InputStream in = new FileInputStream(path); 71 Properties prop = new Properties(); 72 prop.load(in); 73 String driver = prop.getProperty(driver); 74 String url = prop.getProperty(url); 75 String username = prop.getProperty(username); 76 String password = prop.getProperty(password); 77 response.getWriter().println(读取src目录下的db.config包中的perties配置文件：); 78 response.getWriter().println( 79 MessageFormat.format( 80 driver=0,url=1,username=2,password=3, 81 driver,url, username, password); 82 83 84 /* 85 * 通过ServletContext对象读取WebRoot目录下的properties配置文件 86 * param response 87 * throws IOException 88 */ 89 private void readWebRootDirPropCfgFile(HttpServletResponse response) 90 throws IOException 91 /* 92 * 通过ServletContext对象读取WebRoot目录下的properties配置文件 93 * “/”代表的是项目根目录 94 */ 95 InputStream in = this.getServletContext().getResourceAsStream(/perties); 96 Properties prop = new Properties(); 97 prop.load(in); 98 String driver = prop.getProperty(driver); 99 String url = prop.getProperty(url);100 String username = prop.getProperty(username);101 String password = prop.getProperty(password);102 response.getWriter().println(读取WebRoot目录下的perties配置文件：);103 response.getWriter().print(104 MessageFormat.format(105 driver=0,url=1,username=2,password=3, 106 driver,url, username, password);107 108 109 /*110 * 通过ServletContext对象读取src目录下的properties配置文件111 * param response112 * throws IOException113 */114 private void readSrcDirPropCfgFile(HttpServletResponse response) throws IOException 115 /*116 * 通过ServletContext对象读取src目录下的perties配置文件117 */118 InputStream in = this.getServletContext().getResourceAsStream(/WEB-INF/classes/perties);119 Properties prop = new Properties();120 prop.load(in);121 String driver = prop.getProperty(driver);122 String url = prop.getProperty(url);123 String username = prop.getProperty(username);124 String password = prop.getProperty(password);125 response.getWriter().println(读取src目录下的perties配置文件：);126 response.getWriter().println(127 MessageFormat.format(128 driver=0,url=1,username=2,password=3, 129 driver,url, username, password);130 131 132 public void doPost(HttpServletRequest request, HttpServletResponse response)133 throws ServletException, IOException 134 this.doGet(request, response);135 136 137 运行结果如下：代码范例：使用类装载器读取资源文件 1 package gacl.servlet.study; 2 3 import java.io.FileOutputStream; 4 import java.io.IOException; 5 import java.io.InputStream; 6 import java.io.OutputStream; 7 import java.text.MessageFormat; 8 import java.util.Properties; 9 10 import javax.servlet.ServletException; 11 import javax.servlet.http.HttpServlet; 12 import javax.servlet.http.HttpServletRequest; 13 import javax.servlet.http.HttpServletResponse; 14 15 /* 16 * 用类装载器读取资源文件 17 * 通过类装载器读取资源文件的注意事项:不适合装载大文件，否则会导致jvm内存溢出 18 * author gacl 19 * 20 */ 21 public class ServletContextDemo7 extends HttpServlet 22 23 public void doGet(HttpServletRequest request, HttpServletResponse response) 24 throws ServletException, IOException 25 /* 26 * response.setContentType(text/html;charset=UTF-8);目的是控制浏览器用UTF-8进行解码； 27 * 这样就不会出现中文乱码了 28 */ 29 response.setHeader(content-type,text/html;charset=UTF-8); 30 test1(response); 31 response.getWriter().println(); 32 test2(response); 33 response.getWriter().println(); 34 /test3(); 35 test4(); 36 37 38 39 /* 40 * 读取类路径下的资源文件 41 * param response 42 * throws IOException 43 */ 44 private void test1(HttpServletResponse response) throws IOException 45 /获取到装载当前类的类装载器 46 ClassLoader loader = ServletContextDemo7.class.getClassLoader(); 47 /用类装载器读取src目录下的perties配置文件 48 InputStream in = loader.getResourceAsStream(perties); 49 Properties prop = new Properties(); 50 prop.load(in); 51 String driver = prop.getProperty(driver); 52 String url = prop.getProperty(url); 53 String username = prop.getProperty(username); 54 String password = prop.getProperty(password); 55 response.getWriter().println(用类装载器读取src目录下的perties配置文件：); 56 response.getWriter().println( 57 MessageFormat.format( 58 driver=0,url=1,username=2,password=3, 59 driver,url, username, password); 60 61 62 /* 63 * 读取类路径下面、包下面的资源文件 64 * param response 65 * throws IOException 66 */ 67 private void test2(HttpServletResponse response) throws IOException 68 /获取到装载当前类的类装载器 69 ClassLoader loader = ServletContextDemo7.class.getClassLoader(); 70 /用类装载器读取src目录下的gacl.