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Servlet learning notes

2022-07-04 12:27:00 【Kangkang needs to refuel】

Servlet Learning notes

One 、 How to be in Tomcat Configure virtual host in （host）

1. Create a page

establish index.html page 

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> ITBZ </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
</HEAD>
<BODY> Welcome to ITBZ </BODY>
</HTML>

2. modify server.xml add to Host Configuration and addition Context To configure 

<Host name="www.itbz.com"  appBase="webapps"
                 unpackWARs="true" autoDeploy="true">
	<Context path="/itbz" docBase="C:\javatest"/>
	</Host>

3. modify windows Of Host file

Realize domain name and IP The binding of
Host file location

C:\Windows\System32\drivers\etc

4. Access resource test results

Insert picture description here

Two 、HttpServletRequest object

HttpServletRequest Object represents the request of the client browser , When the client browser passes HTTP When the protocol accesses the server ,HTTP All information in the request will be Tomcat Parsed and encapsulated in this object , Through the methods provided by this object , You can get all the information requested by the client .

3、 ... and 、 Get request information

req.getRequestURL()
Returns the complete when the client browser makes a request URL.
req.getRequestURI()
Return the specified resource part of the request line .
req.getRemoteAddr()
Returns the client that made the request IP Address .
req.getLocalAddr()
return WEB Server's IP Address .
req.getLocalPort()
return WEB The server processes Http The protocol connector listens 

// Get request information 
public class DemoServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        StringBuffer requestURL = req.getRequestURL();
        String requestURI = req.getRequestURI();
        String remoteAddr = req.getRemoteAddr();
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        out.println("URL:"+requestURL+"<br/>");
        out.println("URI:"+requestURI+"<br/>");
        out.println("RemoteAddr:"+remoteAddr+"<br/>");
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();

    }
}

stay web.xml in ：

    <servlet>
        <servlet-name>demoServlet</servlet-name>
        <servlet-class>servlet.DemoServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>demoServlet</servlet-name>
        <url-pattern>/demo.do</url-pattern>
    </servlet-mapping>

result ：
Insert picture description here

Four 、 Get request data

stay Servlet How to get the requested data

req.getParameter(“key”)

according to key Get specified value.

// Get request data 
public class GetRequestDataServlet extends HttpServlet {
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        String username = req.getParameter("username");
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        out.println("UserName:"+username+"<br/>");
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
    }
}

HTML Interface ：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="getInfo.do" method="post">
         user name ：<input type="text" name="username"/><br/>
        <input type="submit" value="ok"/>
    </form>
</body>
</html>

web.xml Interface ：

    <servlet>
        <servlet-name>getRequestDataServlet</servlet-name>
        <servlet-class>servlet.GetRequestDataServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getRequestDataServlet</servlet-name>
        <url-pattern>/getInfo.do</url-pattern>
    </servlet-mapping>

5、 ... and 、 Get checkbox data

Get check box (checkbox Components ) The value in

req.getParameterValues(“checkboxkey”)

Get check box (checkbox Components ) The value in , Return to one String[]

public class GetRequestDataServlet extends HttpServlet {
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        String username = req.getParameter("username");
        String[] userlikes = req.getParameterValues("userlike");
        List<String> strings = Arrays.asList(userlikes);
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        out.println("UserName:"+username+"<br/>");
        out.println("UserName:"+strings+"<br/>");
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
    }
}

HTML page ：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <form action="getInfo.do" method="post">
         user name ：<input type="text" name="username"/><br/>
         hobby ：<input type="checkbox" name="userlike" value="sport"/> sports 
            <input type="checkbox" name="userlike" value="music"/> music 
        <input type="submit" value="ok"/>
    </form>
</body>
</html>

6、 ... and 、 Get all submitted data key

Get all submitted data key

req.getParameterNames()

Get all the data in the request key, This method returns an enumeration 

public class GetRequestDataServlet extends HttpServlet {
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        String username = req.getParameter("username");
        String[] userlikes = req.getParameterValues("userlike");
        List<String> strings = Arrays.asList(userlikes);
        Enumeration<String> parameterNames = req.getParameterNames();
        List<String> keys = new ArrayList<>();
        while (parameterNames.hasMoreElements()){
    
            keys.add(parameterNames.nextElement());
        }
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        out.println("UserName:"+username+"<br/>");
        out.println("UserName:"+strings+"<br/>");
        out.println("Keys:"+keys+"<br/>");
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
    }
}

result ：
Insert picture description here

7、 ... and 、 Use Map Structure to get submitted data

req.getParameterMap()

Get all the data in the request and store it in a Map In structure , This method returns a Map, among key by
String type value

public class GetRequestDataServlet extends HttpServlet {
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        String username = req.getParameter("username");
        String[] userlikes = req.getParameterValues("userlike");
        List<String> strings = Arrays.asList(userlikes);
        Enumeration<String> parameterNames = req.getParameterNames();
        List<String> keys = new ArrayList<>();
        while (parameterNames.hasMoreElements()){
    
            keys.add(parameterNames.nextElement());
        }
        Map<String,String[]> parameterMap = req.getParameterMap();
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        out.println("UserName:"+username+"<br/>");
        out.println("UserName:"+strings+"<br/>");
        out.println("Keys:"+keys+"<br/>");
        // Acquisition iterator 
        Iterator<Map.Entry<String,String[]>> iterator = parameterMap.entrySet().iterator();
        while (iterator.hasNext()){
    
            Map.Entry<String,String[]> entry = iterator.next();
            out.println("Keys:" + entry.getKey() +" Value:"+ Arrays.asList(entry.getValue()) +"<br/>");
        }
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
    }
}

8、 ... and 、 Set request encoding

req.setCharacterEncoding(“utf-8”)

The requested packet is transmitted over the network based on bytes ,Tomcat After receiving the requested packet, the
Byte to character . stay Tomcat Is used in ISO-8859-1 The single byte encoding of completes the conversion between bytes and characters ,
Therefore, there will be garbled code if the data contains Chinese , Can pass req.setCharacterEncoding(“utf-8”) Method to mention
Re encode the submitted data according to the specified coding method .

public class GetRequestDataServlet extends HttpServlet {
    
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
            req.setCharacterEncoding("utf-8");
            String username = req.getParameter("username");
            String[] userlikes = req.getParameterValues("userlike");
            List<String> strings = Arrays.asList(userlikes);
            Enumeration<String> parameterNames = req.getParameterNames();
            List<String> keys = new ArrayList<>();
        while (parameterNames.hasMoreElements()){
    
            keys.add(parameterNames.nextElement());
        }
        Map<String,String[]> parameterMap = req.getParameterMap();
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        out.println("UserName:"+username+"<br/>");
        out.println("UserName:"+strings+"<br/>");
        out.println("Keys:"+keys+"<br/>");
        // Acquisition iterator 
        Iterator<Map.Entry<String,String[]>> iterator = parameterMap.entrySet().iterator();
        while (iterator.hasNext()){
    
            Map.Entry<String,String[]> entry = iterator.next();
            out.println("Keys:" + entry.getKey() +" Value:"+ Arrays.asList(entry.getValue()) +"<br/>");
        }
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
    }
}

Nine 、 Resource access method

1. Absolute path

Absolute path access to resources is expressed directly in ”/” As a project Content Path. This method is applicable to ”/” As a project Content Path

<form action="/getInfo.do" method="post">

2. Relative paths

The relative path access resource indicates that it will be relative to the project Content Path As a relative path . This method is applicable to the specific... Specified for the project Content Path

<form action="getInfo.do" method="post">

Ten 、 Get request header information

req.getHeader(“headerKey”)

According to the key Get corresponding value

String headerValue = req.getHeader(“headerKey”);

.

req.getHeaderNames()

Get all in the request header key, This method returns the enumeration class

Enumeration<>

// Get request header information 
public class GetRequestHeaderServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        this.doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        String header = req.getHeader("Accept-Language");
        Enumeration<String> headerNames = req.getHeaderNames();
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        while (headerNames.hasMoreElements()){
    
            String key = headerNames.nextElement();
            String value = req.getHeader(key);
            out.println("key:"+key+" Value:"+value+"<br/>");
        }
        out.println("</BODY>");
        out.println("</HTML>");
    }
}

web.xml:

<servlet>
        <servlet-name>getRequestHeaderServlet</servlet-name>
        <servlet-class>servlet.GetRequestHeaderServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>getRequestHeaderServlet</servlet-name>
        <url-pattern>/getHeader.do</url-pattern>
    </servlet-mapping>

result ： Insert picture description here

11、 ... and 、 Get request header case

demand ： Write a Servlet, If the browser language is zh-CN, Show “ Hello , Smart Chinese ！”, If the browser language is set to en-US, Then it shows “Hello,American”

// Get request header case 
public class LanguageServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        this.doPost(req,resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        String header = req.getHeader("accept-language");
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter out = resp.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC '-//W3C//DTD HTML 4.0 Transitional//EN'>");
        out.println("<HTML>");
        out.println("<HEAD><TITLE> ITBZ </TITLE><HEAD>");
        out.println("<BODY>");
        if (header.indexOf("zh-CN") != -1){
    
            out.println(" Hello , Smart Chinese ！");
        }else if(header.indexOf("en-US") != -1){
    
            out.println("hello,American");
        }else{
    
            out.println(" I'm sorry , The language is not supported ！");
        }
        out.println("</BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }
}

web.xml:

    <servlet>
        <servlet-name>languageServlet</servlet-name>
        <servlet-class>servlet.LanguageServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>languageServlet</servlet-name>
        <url-pattern>/language.do</url-pattern>
    </servlet-mapping>
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