HttpServletResponse相关

叁歲伎倆 2022-04-10 06:09 164阅读 0赞

**目录**

返回给客户端数据：字节流和字符流

解决返回字节流和字符流乱码问题

万能解决乱码

文件下载

tomcat提供的默认下载方式

手动编写的DownloadServlet

--------------------

## 返回给客户端数据：字节流和字符流 ##

package com.zhujunwei.httpServletResponse;
    
    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 HttpServletResponse01 extends HttpServlet {
    	
    	private static final long serialVersionUID = 1L;
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		
    		/**
    		 * 返回给客户端数据两种方式：字节流和字符流方式
    		 * 一次只能执行其中的一个
    		 */
    //		byWriter(resp);
    		byOutputStream(resp);
    		
    		//设置当前这个请求的处理状态码
    //		resp.setStatus(sc);
    		
    		//设置一个头
    //		resp.setHeader(name, value);
    		
    		//设置相应的类型，以及编码
    //		resp.setContentType(type);
    	}
    
    	/**
    	 * 以字节流的方式写数据
    	 * @param resp
    	 * @throws IOException
    	 */
    	private void byOutputStream(HttpServletResponse resp) throws IOException {
    		resp.getOutputStream().write("getOutputStream().write()".getBytes());
    	}
    
    	/**
    	 * 以字符流的方式写数据
    	 * @param resp
    	 * @throws IOException
    	 */
    	@SuppressWarnings("unused")
    	private void byWriter(HttpServletResponse resp) throws IOException {
    		resp.getWriter().write("<h1>getWriter().write()</h1><br>");
    	}
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    }

结果：

getOutputStream().write()

## 解决返回字节流和字符流乱码问题 ##

package com.zhujunwei.httpServletResponse;
    
    import java.io.IOException;
    import java.io.UnsupportedEncodingException;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class HttpServletResponse02 extends HttpServlet {
    	
    	private static final long serialVersionUID = 1L;
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		
    		//字符流输出
    //		writerEncoding(resp);
    		//字节流输出
    		outPutStreamEncoding(resp);
    		
    	}
    	
    	/**
    	 * 解决字节流输出乱码
    	 * @param resp
    	 * @throws IOException
    	 * @throws UnsupportedEncodingException
    	 */
    	private void outPutStreamEncoding(HttpServletResponse resp) throws IOException, UnsupportedEncodingException {
    		//1、指定浏览器看这份数据使用的码表
    		resp.setHeader("Content-Type", "text/html; charset=UTF-8");
    		//2、指定输出的中文用的码表
    		resp.getOutputStream().write("我是最帅的。。".getBytes());
    	}
    	/**
    	 * 解决字符流输出乱码
    	 * @param resp
    	 * @throws IOException
    	 */
    	@SuppressWarnings("unused")
    	private void writerEncoding(HttpServletResponse resp) throws IOException {
    		//这里写出去的文字，默认使用的是ISO-8859-1，我们可以指定写出去的时候，使用什么编码写
    		//1、指定输出到客户端的时候，这些文字使用UTF-8
    		resp.setCharacterEncoding("UTF-8");
    		//2、直接规定浏览器看这份数据的时候，使用什么编码看
    		resp.setHeader("Content-Type", "text/html; charset=UTF-8");
    		
    		resp.getWriter().write("我是最帅的。。。");
    	}
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    }

结果：

我是最帅的。。

## 万能解决乱码 ##

package com.zhujunwei.httpServletResponse;
    
    import java.io.IOException;
    import java.io.UnsupportedEncodingException;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class HttpServletResponse03 extends HttpServlet {
    	
    	private static final long serialVersionUID = 1L;
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		
    		//只需要设置这一行就可以不管是字节或者字符流都不会乱码
    		resp.setContentType("text/html; charset=UTF-8");
    		//字符流输出
    		writerEncoding(resp);
    		//字节流输出
    //		outPutStreamEncoding(resp);
    		
    	}
    	
    	/**
    	 * 解决字节流输出乱码
    	 * @param resp
    	 * @throws IOException
    	 * @throws UnsupportedEncodingException
    	 */
    	@SuppressWarnings("unused")
    	private void outPutStreamEncoding(HttpServletResponse resp) throws IOException, UnsupportedEncodingException {
    		resp.getOutputStream().write("我真的是最帅的。。".getBytes());
    	}
    	/**
    	 * 解决字符流输出乱码
    	 * @param resp
    	 * @throws IOException
    	 */
    	private void writerEncoding(HttpServletResponse resp) throws IOException {
    		resp.getWriter().write("我真的是最帅的。。。");
    	}
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    }

结果

我真的是最帅的。。。

## 文件下载 ##

### tomcat提供的默认下载方式 ###

Tomcat提供的有文件下在的默认Servlet，如果浏览器能打开这种文件的话会自动打开，不会弹出下载框。

我们在项目里面放置几个文件供测试使用

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70][]

download.html

<!DOCTYPE html>
    <html>
    <head>
    <meta charset="UTF-8">
    <title>Insert title here</title>
    </head>
    <body>
    	<h2>tomcat提供的默认下载方式</h2>
    	<a href="download/test.txt">test.txt</a><br>
    	<a href="download/m1.jpg">m1.jpg</a><br>
    	<a href="download/download.rar">download.rar</a><br>
    	<hr>
    	<h2>手动写下载方法</h2>
    	<a href="DownloadServlet?fileName=test.txt">test.txt</a><br>
    	<a href="DownloadServlet?fileName=m1.jpg">m1.jpg</a><br>
    	<a href="DownloadServlet?fileName=download.rar">download.rar</a><br>
    	 
    </body>
    </html>

### 手动编写的DownloadServlet ###

package com.zhujunwei.download;
    
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.io.OutputStream;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class DownloadServlet extends HttpServlet{
    	
    	private static final long serialVersionUID = 1L;
    
    	@Override
    	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		
    		//1、获取要下载的文件名字
    		String fileName = req.getParameter("fileName");
    		
    		//2、获取这个文件在tomcat里面的绝对路径地址
    		String path = getServletContext().getRealPath("download/"+fileName);
    		//让浏览器收到这份资源的时候，以下载的方式提醒用户，而不是直接展示
    		resp.setHeader("Content-Disposition", "attachment; filename="+fileName);
    		
    		//3、转换成输入流
    		InputStream is = new FileInputStream(path);
    		OutputStream os = resp.getOutputStream();
    		
    		int len = 0 ;
    		byte[] buffer = new byte[1024];
    		while((len = is.read(buffer))!=-1) {
    			os.write(buffer,0,len);
    		}
    		os.close();
    		is.close();
    	}
    	
    	@Override
    	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    		doGet(req, resp);
    	}
    }

结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70 1][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70]: /images/20220402/a959d762d43347868b4c66ae7c5b6b20.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70 1]: /images/20220402/dea412798e004f3bb005cdf977dd7f85.png