javaweb學(xué)習(xí)總結(jié)（一）servlet開發(fā)

一河胎、ServletConfig詳解

1.1 配置Servlet初始化參數(shù)

在Servlet的配置文件中惯退，可以使用一個(gè)或多個(gè)<init-param>標(biāo)簽為servlet配置一些初始化參數(shù),例如：

<servlet>
    <servlet-name>ServletConfigDemo1</servlet-name>
    <servlet-class>rain.servlet.study.ServletConfigDemo1</servlet-  
  class>
<!-- 配置ServletConfigDemo1的初始化參數(shù) -->
<init-param>
    <param-name>name</param-name>
    <param-value>rain</param-value>
</init-param>

<init-param>
    <param-name>score</param-name>
    <param-value>140</param-value>
</init-param>

<init-param>
    <param-name>age</param-name>
    <param-value>18</param-value>
</init-param>
</servlet>

1.2 通過(guò)ServletConfig獲取初始化參數(shù)

當(dāng)Servlet配置了初始化參數(shù)以后顺囊，web容器在創(chuàng)建servlet實(shí)例對(duì)象時(shí)其兴，會(huì)自動(dòng)將這些參數(shù)封裝到ServletConfig對(duì)象中去，并且在調(diào)用Servlet的init方法時(shí)會(huì)將ServletConfig傳遞過(guò)去籽御。因此我們可以通過(guò)ServletConfig對(duì)象就可以得到配置的初始化參數(shù)信息了肢执。不過(guò)現(xiàn)在有了servlet3.0之后枉阵，有兩種寫法了。例如：

package rain.servlet.study;
import java.io.IOException;
import java.util.Enumeration;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletConfigDemo1
 */
//@WebServlet(urlPatterns="/ServletConfigDemo1",initParams= {
//      @WebInitParam(name="name",value="rain"),
//      @WebInitParam(name="score",value="100"),
//      @WebInitParam(name="age",value="18")
//})
public class ServletConfigDemo1 extends HttpServlet {
    private static final long serialVersionUID = 1L;

    private ServletConfig config;

/**
 * 當(dāng)servlet配置了初始化參數(shù)時(shí)预茄，web容器在創(chuàng)建servlet實(shí)例對(duì)象時(shí)會(huì)自動(dòng)將這些初始化參數(shù)封裝到servletconfig
 * 對(duì)象中兴溜，并在調(diào)用servlet的init方法時(shí)，將改對(duì)象傳遞給servlet
 */
@Override
public void init(ServletConfig config) throws ServletException {
    // TODO Auto-generated method stub
//      super.init(config);
    this.config = config;
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
//      response.getWriter().append("Served at: ").append(request.getContextPath());
    response.setContentType("text/html;charset=utf-8");
    String paramVal = this.config.getInitParameter("name");
    response.getWriter().print(paramVal);
    response.getWriter().print("<hr/>");
    
    //獲取所有的初始化參數(shù)
    Enumeration<String> e = config.getInitParameterNames();
    while(e.hasMoreElements()) {
        String name = e.nextElement();
        String value = config.getInitParameter(name);
        response.getWriter().print(name + "=" + value + "<br/>");
    }
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    doGet(request, response);
  }

}

上面注釋掉的部分就是Servlet 3.0之后采用注解的形式耻陕，可以看到還是挺方便的拙徽。運(yùn)行結(jié)果如下：

image.png

二、ServletContext對(duì)象

web容器在啟動(dòng)時(shí)诗宣，它會(huì)為每個(gè)web應(yīng)用創(chuàng)建一個(gè)對(duì)應(yīng)的ServletContext對(duì)象斋攀，它代表當(dāng)前web應(yīng)用。
ServletConfig對(duì)象中維護(hù)了ServletContext對(duì)象的引用梧田，可以通過(guò)ServletConfig.getServletContext獲得。
由于一個(gè)web應(yīng)用所有的servlet都共享同一個(gè)ServletContext侧蘸，因此servlet對(duì)象之間可以實(shí)現(xiàn)通訊裁眯。ServletContext對(duì)象通常也被稱之為context域?qū)ο?/p>

三、ServletContext的應(yīng)用

3.1 多個(gè)servlet通過(guò) ServletContext 來(lái)實(shí)現(xiàn)數(shù)據(jù)共享

下面是一個(gè)例子讳癌，兩個(gè)servlet通過(guò)Servletc實(shí)現(xiàn)數(shù)據(jù)共享

package rain.servlet.study;

import java.io.IOException;

import javax.servlet.ServletContext;
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 RainServletContextDemo1
 */
@WebServlet("/RainServletContextDemo1")
public class RainServletContextDemo1 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.getWriter().append("Served at:     ").append(request.getContextPath());
        String data = "rain_sample_data";
        /**
         * ServletConfig對(duì)象中維護(hù)了ServletContext的引用穿稳，可以通過(guò)
         * getServletConfig().getServletContext()來(lái)獲取到。
         */
        ServletContext context = this.getServletConfig().getServletContext();
        context.setAttribute("data", data);
}

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

下面是另外一個(gè)Servlet

package rain.servlet.study;

import java.io.IOException;

import javax.servlet.ServletContext;
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 RainServletContextDemo2
 */
@WebServlet("/RainServletContextDemo2")
public class RainServletContextDemo2 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.getWriter().append("Served at: ").append(request.getContextPath());
        ServletContext context = getServletContext();
        String data = (String) context.getAttribute("data");//從ServletContext對(duì)象中取出數(shù)據(jù)
        response.getWriter().print("data="+data);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

先運(yùn)行RainServletContextDemo1晌坤，然后再運(yùn)行RainServletContextDemo2逢艘，即可以實(shí)現(xiàn)數(shù)據(jù)的共享。運(yùn)行結(jié)果如下：

image.png

3.2 用ServletContext對(duì)象實(shí)現(xiàn)請(qǐng)求轉(zhuǎn)發(fā)

RainServletContextDemo3

package rain.servlet.study;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
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 RainServletContextDemo3
 */
@WebServlet("/RainServletContextDemo3")
public class RainServletContextDemo3 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.getWriter().append("Served at: ").append(request.getContextPath());
        String data = "i am servlet3";
        response.getOutputStream().write(data.getBytes());
        ServletContext context = getServletContext();
        RequestDispatcher dispatcher = context.getRequestDispatcher("/RainServletContextDemo4");
        dispatcher.forward(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

RainServletContextDemo4

package rain.servlet.study;
import java.io.IOException;
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 RainServletContextDemo4
 */
@WebServlet("/RainServletContextDemo4")
public class RainServletContextDemo4 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.getOutputStream().write("i am servlet4 hia!!!".getBytes());
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

3.3 用ServletContext對(duì)象讀取資源文件

項(xiàng)目的目錄結(jié)構(gòu)：

image.png

代碼：使用Servlet讀取資源文件

package rain.servlet.study;

import java.io.IOException;
import java.io.InputStream;
import java.text.MessageFormat;
import java.util.Properties;
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 RainServletContextDemo5
 * 使用ServletContext讀取資源文件
 */
@WebServlet("/RainServletContextDemo5")
public class RainServletContextDemo5 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.getWriter().append("Served at: ").append(request.getContextPath());
        response.setHeader("content-type", "text/html;charset=UTF-8");
        readSrcDirFile(response);//讀取src目錄下面的文件
        response.getWriter().write("<hr/>");
        readWebContentFile(response);//讀取webcontent目錄下面的文件
        response.getWriter().write("<hr/>");
        readPackageFile(response);//讀取rain.servlet.study目錄下的文件
        response.getWriter().write("<hr/>");
        readDataConfigFile(response);//讀取data.config下的文件 
    }

    /**
     * 讀取data.config下的文件 data1.properties
     * @param response
     * @throws IOException 
     */
    private void readDataConfigFile(HttpServletResponse response) throws IOException {
        InputStream in = getServletContext().getResourceAsStream(
            "/WEB-INF/classes/data/config/data1.properties");
        Properties prop = new Properties();
        prop.load(in);
        String name = prop.getProperty("name");
        String data = prop.getProperty("data");
        String time = prop.getProperty("time");
        response.getWriter().println("讀取的是data.config包下面的data2.properties:");
        response.getWriter().println(
            MessageFormat.format("name={0},data={1},time={2}", 
                    name,data,time));
}

/**
 * readPackageFile(response);//讀取rain.servlet.study目錄下的文件  data2.properties
 * @param response
 * @throws IOException 
 */
private void readPackageFile(HttpServletResponse response) throws IOException {
    InputStream in = getServletContext().getResourceAsStream(
            "/WEB-INF/classes/rain/servlet/study/data2.properties");
    Properties prop = new Properties();
    prop.load(in);
    String name = prop.getProperty("name");
    String data = prop.getProperty("data");
    String time = prop.getProperty("time");
    response.getWriter().println("讀取的是src目錄下面rain.servlet.study包下面的data2.properties:");
    response.getWriter().println(
            MessageFormat.format("name={0},data={1},time={2}", 
                    name,data,time));
}

/**
 * 讀取webcontent目錄下面的文件 data4.properties
 * @param response
 * @throws IOException 
 */
private void readWebContentFile(HttpServletResponse response) throws IOException {
    InputStream in = getServletContext().getResourceAsStream(
            "/data4.properties");
    Properties prop = new Properties();
    prop.load(in);
    String name = prop.getProperty("name");
    String data = prop.getProperty("data");
    String time = prop.getProperty("time");
    response.getWriter().println("讀取的是webcontent目錄下面的data4.properties:");
    response.getWriter().println(
            MessageFormat.format("name={0},data={1},time={2}", 
                    name,data,time));
}

/**
 * 讀取src目錄下面的文件 data3.properties
 * @param response
 * @throws IOException 
 */
private void readSrcDirFile(HttpServletResponse response) throws IOException {
    InputStream in = getServletContext().getResourceAsStream(
            "/WEB-INF/classes/data3.properties");
    Properties prop = new Properties();
    prop.load(in);
    String name = prop.getProperty("name");
    String data = prop.getProperty("data");
    String time = prop.getProperty("time");
    response.getWriter().println("讀取的是src目錄下面的data3.properties:");
    response.getWriter().println(
            MessageFormat.format("name={0},data={1},time={2}", 
                    name,data,time));
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
        doGet(request, response);
    }

}

運(yùn)行結(jié)果如下：

image.png

四污抬、在客戶端緩存Servlet的輸出

對(duì)于不是經(jīng)常變化的數(shù)據(jù)酗宋，可以在服務(wù)器端設(shè)置一個(gè)緩存時(shí)間臂拓，以避免瀏覽器頻繁的向服務(wù)器端發(fā)起請(qǐng)求，提高服務(wù)器的性能央拖。

代碼如下：

package rain.servlet.study;

import java.io.IOException;
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 RainServletDemo6
 */
@WebServlet("/RainServletDemo6")
public class RainServletDemo6 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.getWriter().append("Served at: ").append(request.getContextPath());
        String data = "asdffffdsgsgsfgsgsgs";
        response.setDateHeader("expires", System.currentTimeMillis()+24*3600*1000);
        response.getWriter().println(data);
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

運(yùn)行結(jié)果

image.png

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javaweb學(xué)習(xí)總結(jié)（一）servlet開發(fā)

一河胎、ServletConfig詳解

1.1 配置Servlet初始化參數(shù)

1.2 通過(guò)ServletConfig獲取初始化參數(shù)

二、ServletContext對(duì)象

三、ServletContext的應(yīng)用

3.1 多個(gè)servlet通過(guò) ServletContext 來(lái)實(shí)現(xiàn)數(shù)據(jù)共享

3.2 用ServletContext對(duì)象實(shí)現(xiàn)請(qǐng)求轉(zhuǎn)發(fā)

3.3 用ServletContext對(duì)象讀取資源文件

項(xiàng)目的目錄結(jié)構(gòu)：

代碼：使用Servlet讀取資源文件

運(yùn)行結(jié)果如下：

四污抬、在客戶端緩存Servlet的輸出

代碼如下：

運(yùn)行結(jié)果

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