javaweb Servlet开发总结（二）

<servlet>
 <servlet-name>servletconfigdemo1</servlet-name>
 <servlet-class>gacl.servlet.study.servletconfigdemo1</servlet-class>
 <!--配置servletconfigdemo1的初始化参数 -->
 <init-param>
  <param-name>name</param-name>
  <param-value>gacl</param-value>
 </init-param>
  <init-param>
  <param-name>password</param-name>
  <param-value>123</param-value>
 </init-param>
 <init-param>
  <param-name>charset</param-name>
  <param-value>utf-8</param-value>
 </init-param>
</servlet>

package gacl.servlet.study;

import java.io.ioexception;
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;

public class servletconfigdemo1 extends httpservlet {

 /**
  * 定义servletconfig对象来接收配置的初始化参数
  */
 private servletconfig config;
 
 /**
  * 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，程序员通过servletconfig对象就可以
  * 得到当前servlet的初始化参数信息。
  */
 @override
 public void init(servletconfig config) throws servletexception {
  this.config = config;
 }

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  //获取在web.xml中配置的初始化参数
  string paramval = this.config.getinitparameter("name");//获取指定的初始化参数
  response.getwriter().print(paramval);
  
  response.getwriter().print("<hr/>");
  //获取所有的初始化参数
  enumeration<string> e = config.getinitparameternames();
  while(e.hasmoreelements()){
   string name = e.nextelement();
   string value = config.getinitparameter(name);
   response.getwriter().print(name + "=" + value + "<br/>");
  }
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  this.doget(request, response);
 }

}

package gacl.servlet.study;

import java.io.ioexception;
import javax.servlet.servletcontext;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

public class servletcontextdemo1 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  string data = "xdp_gacl";
  /**
   * 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。
   */
  servletcontext context = this.getservletconfig().getservletcontext();//获得servletcontext对象
  context.setattribute("data", data); //将data存储到servletcontext对象中
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  doget(request, response);
 }
}

package gacl.servlet.study;

import java.io.ioexception;
import javax.servlet.servletcontext;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

public class servletcontextdemo2 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  servletcontext context = this.getservletcontext();
  string data = (string) context.getattribute("data");//从servletcontext对象中取出数据
  response.getwriter().print("data="+data);
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  doget(request, response);
 }
}

<?xml version="1.0" encoding="utf-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/xmlschema-instance" xsi:schemalocation="http://java.sun.com/xml/ns/javaee 
 http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
 <display-name></display-name>
 <!-- 配置web应用的初始化参数 -->
 <context-param>
  <param-name>url</param-name>
  <param-value>jdbc:mysql://localhost:3306/test</param-value>
 </context-param>

 <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
</web-app>

package gacl.servlet.study;

import java.io.ioexception;
import javax.servlet.servletcontext;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;


public class servletcontextdemo3 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {

  servletcontext context = this.getservletcontext();
  //获取整个web站点的初始化参数
  string contextinitparam = context.getinitparameter("url");
  response.getwriter().print(contextinitparam);
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  doget(request, response);
 }

}

package gacl.servlet.study;

import java.io.ioexception;
import java.io.printwriter;
import javax.servlet.requestdispatcher;
import javax.servlet.servletcontext;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

public class servletcontextdemo4 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  string data = "<h1><font color='red'>abcdefghjkl</font></h1>";
  response.getoutputstream().write(data.getbytes());
  servletcontext context = this.getservletcontext();//获取servletcontext对象
  requestdispatcher rd = context.getrequestdispatcher("/servlet/servletcontextdemo5");//获取请求转发对象(requestdispatcher)
  rd.forward(request, response);//调用forward方法实现请求转发
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
 }
}

package gacl.servlet.study;

import java.io.ioexception;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

public class servletcontextdemo5 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  response.getoutputstream().write("servletdemo5".getbytes());
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  this.doget(request, response);
 }

}

package gacl.servlet.study;

import java.io.fileinputstream;
import java.io.filenotfoundexception;
import java.io.ioexception;
import java.io.inputstream;
import java.text.messageformat;
import java.util.properties;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

/**
 * 使用servletcontext读取资源文件
 * 
 * @author gacl
 * 
 */
public class servletcontextdemo6 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception { 
  /**
   * response.setcontenttype("text/html;charset=utf-8");目的是控制浏览器用utf-8进行解码；
   * 这样就不会出现中文乱码了
   */
  response.setheader("content-type","text/html;charset=utf-8");
  readsrcdirpropcfgfile(response);//读取src目录下的properties配置文件
  response.getwriter().println("<hr/>");
  readwebrootdirpropcfgfile(response);//读取webroot目录下的properties配置文件
  response.getwriter().println("<hr/>");
  readpropcfgfile(response);//读取src目录下的db.config包中的db3.properties配置文件
  response.getwriter().println("<hr/>");
  readpropcfgfile2(response);//读取src目录下的gacl.servlet.study包中的db4.properties配置文件
  
 }

 /**
  * 读取src目录下的gacl.servlet.study包中的db4.properties配置文件
  * @param response
  * @throws ioexception
  */
 private void readpropcfgfile2(httpservletresponse response)
   throws ioexception {
  inputstream in = this.getservletcontext().getresourceasstream("/web-inf/classes/gacl/servlet/study/db4.properties");
  properties prop = new properties();
  prop.load(in);
  string driver = prop.getproperty("driver");
  string url = prop.getproperty("url");
  string username = prop.getproperty("username");
  string password = prop.getproperty("password");
  response.getwriter().println("读取src目录下的gacl.servlet.study包中的db4.properties配置文件：");
  response.getwriter().println(
    messageformat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 读取src目录下的db.config包中的db3.properties配置文件
  * @param response
  * @throws filenotfoundexception
  * @throws ioexception
  */
 private void readpropcfgfile(httpservletresponse response)
   throws filenotfoundexception, ioexception {
  //通过servletcontext获取web资源的绝对路径
  string path = this.getservletcontext().getrealpath("/web-inf/classes/db/config/db3.properties");
  inputstream in = new fileinputstream(path);
  properties prop = new properties();
  prop.load(in);
  string driver = prop.getproperty("driver");
  string url = prop.getproperty("url");
  string username = prop.getproperty("username");
  string password = prop.getproperty("password");
  response.getwriter().println("读取src目录下的db.config包中的db3.properties配置文件：");
  response.getwriter().println(
    messageformat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 通过servletcontext对象读取webroot目录下的properties配置文件
  * @param response
  * @throws ioexception
  */
 private void readwebrootdirpropcfgfile(httpservletresponse response)
   throws ioexception {
  /**
   * 通过servletcontext对象读取webroot目录下的properties配置文件
   * “/”代表的是项目根目录
   */
  inputstream in = this.getservletcontext().getresourceasstream("/db2.properties");
  properties prop = new properties();
  prop.load(in);
  string driver = prop.getproperty("driver");
  string url = prop.getproperty("url");
  string username = prop.getproperty("username");
  string password = prop.getproperty("password");
  response.getwriter().println("读取webroot目录下的db2.properties配置文件：");
  response.getwriter().print(
    messageformat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 通过servletcontext对象读取src目录下的properties配置文件
  * @param response
  * @throws ioexception
  */
 private void readsrcdirpropcfgfile(httpservletresponse response) throws ioexception {
  /**
   * 通过servletcontext对象读取src目录下的db1.properties配置文件
   */
  inputstream in = this.getservletcontext().getresourceasstream("/web-inf/classes/db1.properties");
  properties prop = new properties();
  prop.load(in);
  string driver = prop.getproperty("driver");
  string url = prop.getproperty("url");
  string username = prop.getproperty("username");
  string password = prop.getproperty("password");
  response.getwriter().println("读取src目录下的db1.properties配置文件：");
  response.getwriter().println(
    messageformat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  this.doget(request, response);
 }

}

package gacl.servlet.study;

import java.io.fileoutputstream;
import java.io.ioexception;
import java.io.inputstream;
import java.io.outputstream;
import java.text.messageformat;
import java.util.properties;

import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

/**
 * 用类装载器读取资源文件
 * 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
 * @author gacl
 *
 */
public class servletcontextdemo7 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  /**
   * response.setcontenttype("text/html;charset=utf-8");目的是控制浏览器用utf-8进行解码；
   * 这样就不会出现中文乱码了
   */
  response.setheader("content-type","text/html;charset=utf-8");
  test1(response);
  response.getwriter().println("<hr/>");
  test2(response);
  response.getwriter().println("<hr/>");
  //test3();
  test4();
  
 }
 
 /**
  * 读取类路径下的资源文件
  * @param response
  * @throws ioexception
  */
 private void test1(httpservletresponse response) throws ioexception {
  //获取到装载当前类的类装载器
  classloader loader = servletcontextdemo7.class.getclassloader();
  //用类装载器读取src目录下的db1.properties配置文件
  inputstream in = loader.getresourceasstream("db1.properties");
  properties prop = new properties();
  prop.load(in);
  string driver = prop.getproperty("driver");
  string url = prop.getproperty("url");
  string username = prop.getproperty("username");
  string password = prop.getproperty("password");
  response.getwriter().println("用类装载器读取src目录下的db1.properties配置文件：");
  response.getwriter().println(
    messageformat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }

 /**
  * 读取类路径下面、包下面的资源文件
  * @param response
  * @throws ioexception
  */
 private void test2(httpservletresponse response) throws ioexception {
  //获取到装载当前类的类装载器
  classloader loader = servletcontextdemo7.class.getclassloader();
  //用类装载器读取src目录下的gacl.servlet.study包中的db4.properties配置文件
  inputstream in = loader.getresourceasstream("gacl/servlet/study/db4.properties");
  properties prop = new properties();
  prop.load(in);
  string driver = prop.getproperty("driver");
  string url = prop.getproperty("url");
  string username = prop.getproperty("username");
  string password = prop.getproperty("password");
  response.getwriter().println("用类装载器读取src目录下的gacl.servlet.study包中的db4.properties配置文件：");
  response.getwriter().println(
    messageformat.format(
      "driver={0},url={1},username={2},password={3}", 
      driver,url, username, password));
 }
 
 /**
  * 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
  */
 public void test3() {
  /**
   * 01.avi是一个150多m的文件，使用类加载器去读取这个大文件时会导致内存溢出：
   * java.lang.outofmemoryerror: java heap space
   */
  inputstream in = servletcontextdemo7.class.getclassloader().getresourceasstream("01.avi");
  system.out.println(in);
 }
 
 /**
  * 读取01.avi,并拷贝到e:\根目录下
  * 01.avi文件太大，只能用servletcontext去读取
  * @throws ioexception
  */
 public void test4() throws ioexception {
  // path=g:\java学习视频\javaweb学习视频\javaweb\day05视频\01.avi
  // path=01.avi
  string path = this.getservletcontext().getrealpath("/web-inf/classes/01.avi");
  /**
   * path.lastindexof("\\") + 1是一个非常绝妙的写法
   */
  string filename = path.substring(path.lastindexof("\\") + 1);//获取文件名
  inputstream in = this.getservletcontext().getresourceasstream("/web-inf/classes/01.avi");
  byte buffer[] = new byte[1024];
  int len = 0;
  outputstream out = new fileoutputstream("e:\\" + filename);
  while ((len = in.read(buffer)) > 0) {
   out.write(buffer, 0, len);
  }
  out.close();
  in.close();
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {

  this.doget(request, response);
 }

}

package gacl.servlet.study;

import java.io.ioexception;

import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;

public class servletdemo5 extends httpservlet {

 public void doget(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {
  string data = "abcddfwerwesfasfsadf";
  /**
   * 设置数据合理的缓存时间值，以避免浏览器频繁向服务器发送请求，提升服务器的性能
   * 这里是将数据的缓存时间设置为1天
   */
  response.setdateheader("expires",system.currenttimemillis() + 24 * 3600 * 1000);
  response.getoutputstream().write(data.getbytes());
 }

 public void dopost(httpservletrequest request, httpservletresponse response)
   throws servletexception, ioexception {

  this.doget(request, response);
 }

}