HttpServletResponse
我们在创建Servlet时会覆盖service()方法，或doGet()/doPost(),这些方法都有两个参数，一个为代表请求的request和代表响应response。
service方法中的response的类型是ServletResponse，而doGet/doPost方法的response的类型是HttpServletResponse，HttpServletResponse是ServletResponse的子接口，功能和方法更加强大
response设置响应行
设置响应行的状态码
setStatus(int sc)1
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23package com.rexyan.response;
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 Response extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//通过修改状态码和头的方式实现跳转
response.setStatus(301);
response.setHeader("Location", "http://www.baidu.com");
//实际开发中使用这种方式
response.sendRedirect("http://www.baidu.com");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
response设置响应头
addHeader(String name, String value)
addIntHeader(String name, int value)
addDateHeader(String name, long date)
setHeader(String name, String value) 【经常用】
setDateHeader(String name, long date)
setIntHeader(String name, int value)
其中，add表示添加，而set表示设置1
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19package com.rexyan.response;
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 Response extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setHeader("name", "rex");
response.addHeader("name", "lisi");
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
通过response设置响应体
PrintWriter getWriter()获得字符流 通过字符流的write(Strings)方法可以将字符串设置到response缓冲区中，随后Tomcat会将response缓冲区中的内容组装成Http响应返回给浏览器端。
关于设置中文的乱码问题，原因：response缓冲区的默认编码是iso8859-1，此码表中没有中文，可以通过response的setCharacterEncoding(String charset) 设置response的编码
但我们发现客户端还是不能正常显示文字原因：我们将response缓冲区的编码设置成UTF-8，但浏览器的默认编码是本地系 统的编码，因为我们都是中文系统，所以客户端浏览器的默认编码是GBK，我们可以 手动修改浏览器的编码是UTF-8。
我们还可以在代码中指定浏览器解析页面的编码方式，
通过response的setContentType(String type)方法指定页面解析时的编码是UTF-8
response.setContentType(“text/html;charset=UTF-8”);
上面的代码不仅可以指定浏览器解析页面时的编码，同时也内含setCharacterEncoding的功能，所以在实际开发中只要编写response.setContentType(“text/html;charset=UTF-8”);就可以解决页面输出中文乱码问题。1
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21package com.rexyan.response;
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 Response extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=utf-8");
response.getWriter().write("中国");
//在实际开发中其实只需要使用response.setContentType("text/html;charset=utf-8");设置即可
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
获取文件的绝对路径
1 | String realPath = getServletContext().getRealPath("a.jpg"); |
响应头设置字节
ServletOutputStream getOutputStream()
获得字节流，通过该字节流的write(byte[] bytes)可以向response缓冲区中写入字节，在由Tomcat服务器将字节内容组成Http响应返回给浏览器。1
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32package com.rexyan.response;
import java.io.FileInputStream;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Response extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//传入相对路径通过ServerLetContext获取文件的绝对路径
String realPath = getServletContext().getRealPath("a.jpg");
//使用IO读取文件
FileInputStream fileInputStream = new FileInputStream(realPath);
//将文件写到response缓冲区
ServletOutputStream outputStream = response.getOutputStream();
int len = 0;
byte[] buffer = new byte[1024];
while ((len=fileInputStream.read(buffer))>0) {
outputStream.write(buffer, 0, len);
}
fileInputStream.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
下载文件
1 | package com.rexyan.response; |
文件下载出现乱码
但是，如果下载中文文件，页面在下载时会出现中文乱码或不能显示文件名的情况， 原因是不同的浏览器默认对下载文件的编码方式不同，ie是UTF-8编码方式，而火狐 浏览器是Base64编码方式。所里这里需要解决浏览器兼容性问题，解决浏览器兼容 性问题的首要任务是要辨别访问者是ie还是火狐（其他），通过Http请求体中的User-Agent属性可以辨别1
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15if (agent.contains("MSIE")) {
// IE浏览器
filename = URLEncoder.encode(filename, "utf-8");
filename = filename.replace("+", " ");
} else if (agent.contains("Firefox")) {
// 火狐浏览器
BASE64Encoder base64Encoder = new BASE64Encoder();
filename = "=?utf-8?B?"
+ base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
} else {
// 其它浏览器
filename = URLEncoder.encode(filename, "utf-8");
}
其中agent就是请求头User-Agent的值
代码实现如下：1
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62package com.rexyan.response;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import sun.misc.BASE64Encoder;
public class Response extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String agent = request.getHeader("User-Agent");
String filename = "a.jpg";
String downname = filename;
if (agent.contains("MSIE")) {
// IE浏览器
downname = URLEncoder.encode(filename, "utf-8");
downname = filename.replace("+", " ");
} else if (agent.contains("Firefox")) {
// 火狐浏览器
BASE64Encoder base64Encoder = new BASE64Encoder();
downname = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
} else {
// 其它浏览器
downname = URLEncoder.encode(filename, "utf-8");
}
//若要下载文件，需加上两个头文件
//通过getMimeType传入文件名获取文件的Mime类型
response.setContentType(getServletContext().getMimeType(filename));
//设置头文件,告诉浏览器以下载的方式打开文件
response.setHeader("Content-Disposition", "attachment;filename="+ downname);
//------------------------------------------------------------------
//传入相对路径通过ServerLetContext获取文件的绝对路径
String realPath = getServletContext().getRealPath(filename);
//使用IO读取文件
FileInputStream fileInputStream = new FileInputStream(realPath);
//将文件写到response缓冲区
ServletOutputStream outputStream = response.getOutputStream();
int len = 0;
byte[] buffer = new byte[1024];
while ((len=fileInputStream.read(buffer))>0) {
outputStream.write(buffer, 0, len);
}
fileInputStream.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}