HTTP协议：（2）HTTP请求案例

HttpServletRequest对象核心API

类别	API
请求行	request.getMethod(); 请求方式 request.getRequetURI() / request.getRequetURL() 请求资源 request.getProtocol() 请求http协议版本
请求头	request.getHeader("名称") 根据请求头获取请求值 request.getHeaderNames() 获取所有的请求头名称
实体内容	request.getInputStream() 获取实体内容数据
GET方式获取请求参数	request.getQueryString();
POST方式获取请求参数	request.getInputStream();
GET和POST获取 参数的方法(通用)	request.getParameter("参数名"); 根据参数名获取参数值（注意，只能获取一个值的参数） request.getParameterValue("参数名“)；根据参数名获取参数值（可以获取多个值的参数） request.getParameterNames(); 获取所有参数名称列表

1、获取请求行、请求头、实体内部的信息

package com.rk.http.a_request;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 请求数据的请求行、请求头、实体内容
*/
public class Demo01 extends HttpServlet
{
/*
* 1)tomcat服务器接收到浏览器发送的请求数据，然后封装到HttpServetRequest对象中
* 2)tomcat服务器调用doGet方法，然后把request对象传入到servlet中。
* 3)从request对象取出请求数据。
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
this.doPost(request, response);
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
response.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
printRequestLine(request, response);
printRequestHeaders(request, response);
printRequestBody(request, response);//这里只有通过post方式提交的表单数据才能被打印出来
}

/**
* 请求行
*/
private void printRequestLine(HttpServletRequest request, HttpServletResponse response) throws IOException
{
PrintWriter out = response.getWriter();

String strMethod = request.getMethod();//请求方式
StringBuffer strURL = request.getRequestURL();//请求资源
String strURI = request.getRequestURI();
String strProtocol = request.getProtocol();//http协议

out.write("<h1>请求行(Request Line)</h1>");
out.write("<strong>Request Method</strong>: " + strMethod + "<br/>");
out.write("<strong>Request URI</strong>: " + strURI + "<br/>");
out.write("<strong>Request URL</strong>: " + strURL + "<br/>");
out.write("<strong>Request Protocol</strong>: " + strProtocol + "<br/>");
out.write("<hr/>");
}

/**
* 请求头
*/
private void printRequestHeaders(HttpServletRequest request, HttpServletResponse response) throws IOException
{
PrintWriter out = response.getWriter();
out.write("<h1>请求头(Request Headers)</h1>");

//遍历所有请求头
Enumeration<String> requestHeaders = request.getHeaderNames();//得到所有的请求头名称列表
while(requestHeaders.hasMoreElements())//判断是否有下一个元素
{
String headerName = requestHeaders.nextElement();//取出下一个元素
String headerValue = request.getHeader(headerName);//根据头名称的到头的内容
out.write("<strong>" + headerName + "</strong>: " + headerValue + "<br/>");
}
out.write("<hr/>");
}

/**
* 请求的实体内容
*/
private void printRequestBody(HttpServletRequest request, HttpServletResponse response) throws IOException
{
PrintWriter out = response.getWriter();
out.write("<h1>实体内容(Request Body)</h1>");

ServletInputStream inStream = request.getInputStream();//得到实体内容
byte[] buf = new byte[1024];
int len = 0;
while((len=inStream.readLine(buf, 0, buf.length)) != -1)
{
String strValue = new String(buf, 0, len);
out.print(strValue);
}
out.write("<hr/>");
}

}

2、获取浏览器的类型

获取浏览器的类型主要是依据HTTP请求头中的user-agent。

package com.rk.http.a_request;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 案例：获取浏览器的类型
*/
public class Demo02 extends HttpServlet
{
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");//ContentType可以参照%tomcat%/conf/web.xml文件中的内容
PrintWriter out = response.getWriter();

StringBuilder sb = new StringBuilder();
sb.append("你正在使用的是");
String userAgent = request.getHeader("user-agent");//获取请求头： user-agent

//判断用户使用的浏览器类型
if(userAgent.contains("Chrome"))
{
sb.append("Chrome");
}
else if(userAgent.contains("Firefox"))
{
sb.append("Firefox");
}
else if(userAgent.contains("Trident"))
{
sb.append("IE");
}
else
{
sb.append("未知的");
}
sb.append("浏览器");
out.write(sb.toString());
}
}

3、防止非法链接

防止非法链接主要是依据HTTP请求头中的referer。

package com.rk.http.a_request;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 案例:防止非法链接
* 这是需要下载的资源
*/
public class Demo03 extends HttpServlet
{
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException ,IOException
{
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");

String referer = request.getHeader("referer");//得到referer头
System.out.println("referer: " + referer);

/**
* 判断非法链接：
* 	1）直接访问的话referer==null
*  2）如果当前请求不是来自广告
*/
if((referer == null) || !(referer.contains("/RK007HTTP/ad.html")))
{
response.getWriter().write("当前是非法链接，请回到首页。<a href='/RK007HTTP/ad.html'>首页</a>");
}
else
{
response.getWriter().write("资源正在下载...");
}
}
}

4、获取GET方式和Post方式提交的参数

package com.rk.http.a_request;

import java.io.IOException;
import java.io.InputStream;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 获取GET方式和Post方式提交的参数
*/
public class Demo04 extends HttpServlet
{
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");
String queryString = request.getQueryString();//获取到QueryString
response.getWriter().write("<h1>通过GET方式获取提交的表单参数</h1>");
response.getWriter().write(queryString);
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");
response.getWriter().write("<h1>通过POST方式获取提交的表单参数</h1>");
InputStream inStream = request.getInputStream();//获取到InputStream
byte[] buf = new byte[1024];
int len = 0;
while((len = inStream.read(buf, 0, buf.length)) != -1)
{
String postData = new String(buf,0,len);
response.getWriter().write(postData);
}
}

}

5、请求参数编码问题

参数编码问题的原因：a)浏览器默认情况下以UTF-8编码向Tomcat服务器发送HTTP请求。
同样，Tomcat在接收到HTTP请求时，默认以iso-8859-1进行解码。b)如果HTTP请求中的数据是英文字符，由于UTF-8对iso-8859-1字符集的兼容性，因此不会出现乱码的问题。c)如果HTTP请求中的数据是中文字符，由于字符编码和解码的不同，就会出乱码的情况。要解决乱码的问题，就需要进行编码的转换，思路如下：
String str --> byte[] bytes --> String newString首先，得到到Tomcat接收到的字符串str；其次，用iso-8859-1编码方式获取到字符串str的字节数组bytes；最后，用utf-8编码的方式将字节数组bytes转换为新的字符串newString。GET方式和POST方式解决乱码问题的一些差异通过GET方式传递的参数，只能通过对每一个传递的参数进行编码转换。而通过POST方式传递的参数，除了对每个传递的参数进行编码转换之外，
还有一种简单的方式，就是使用request.setCharacterEncoding("UTF-8");这样后续获取参数时就不需要再进行编码转换了。

package com.rk.http.a_request;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.util.Arrays;
import java.util.Enumeration;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Demo05 extends HttpServlet
{

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.write("<h1>"+request.getMethod()+"方式</h1>");

Enumeration<String> paramEnum =  request.getParameterNames();
while(paramEnum.hasMoreElements())
{
String paramName = paramEnum.nextElement();
if(paramName.equals("hobby"))//如果参数名是hobby，则调用getParameterValues
{
String[] hobbies_iso_8859_1 = request.getParameterValues("hobby");//根据参数名获取参数值（可以获取多个值的同名参数）
String[] hobbies = new String[hobbies_iso_8859_1.length];
for(int i=0;i<hobbies_iso_8859_1.length;i++)
{
hobbies[i] = convertToUTF8Encoding(hobbies_iso_8859_1[i]);
}
out.write(paramName + ": " + Arrays.toString(hobbies) + "<br/>");
}
else
{
String paramValue_iso_8859_1 = request.getParameter(paramName);// 根据参数名得到参数值(只能获取一个值的参数)
String paramValue = convertToUTF8Encoding(paramValue_iso_8859_1);
out.write(paramName + ": " + paramValue + "<br/>");
}

}
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
/**
* 设置参数查询的编码request.setCharacterEncoding("UTF-8");
* 该方法只能对请求实体内容的数据编码起作用。POST提交的数据在实体内容中，所以该方法对POST方法有效！
* GET方法的参数放在URI后面，所以对GET方式无效！！！
* Overrides the name of the character encoding used in the body of this request.
* This method must be called prior to reading request parameters or reading input using getReader().
*/
request.setCharacterEncoding("UTF-8");

response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
out.write("<h1>"+request.getMethod()+"方式</h1>");

Enumeration<String> paramEnum =  request.getParameterNames();
while(paramEnum.hasMoreElements())
{
String paramName = paramEnum.nextElement();
if(paramName.equals("hobby"))//如果参数名是hobby，则调用getParameterValues
{
String[] hobbies = request.getParameterValues("hobby");//根据参数名获取参数值（可以获取多个值的同名参数）
out.write(paramName + ": " + Arrays.toString(hobbies) + "<br/>");
}
else
{
String paramValue = request.getParameter(paramName);// 根据参数名得到参数值(只能获取一个值的参数)
out.write(paramName + ": " + paramValue + "<br/>");
}
}
}

/**
* 手动重新解码(iso-8859-1 字符串-> utf-8 字符串)
*/
private String convertToUTF8Encoding(String orginalString) throws IOException
{
return new String(orginalString.getBytes("iso-8859-1"),"UTF-8");
}

}