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<>Response响应数据
<>1. response将字符数据返回到浏览器
需要两步：
* 通过response对象获取字符输出流PrintWriter writer = resp.getWriter();
* 通过字符输出流写数据：writer.writer(“aaa”);
案例
浏览器中打印出字符 /** * 响应字符数据：设置字符数据的响应体 */ @WebServlet("/resp3") public class
ResponseDemo3 extends HttpServlet { @Override protected void doGet(
HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException { response.setContentType(
"text/html;charset=utf-8"); //1. 获取字符输出流 PrintWriter writer = response.getWriter
(); writer.write("aaa"); } @Override protected void doPost(HttpServletRequest
request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response); } }
还可以返回html字符串，并且浏览器能解析出来，如下：
PrintWriter writer = response.getWriter();
//content-type，告诉浏览器返回的数据类型是HTML类型数据，这样浏览器才会解析HTML标签 response.setHeader(
"content-type","text/html"); writer.write("<h1>aaa</h1>");
注意： 一次请求响应结束后，response对象就会被销毁，所以不要手动关闭流
提醒 如果要返回一个中文字符串你好，需要设置响应数据编码为utf-8
//设置响应的数据格式及数据的编码 response.setContentType("text/html;charset=utf-8"); writer.
write("你好");
<>2. response响应字节数据
需要将字节数据写回到浏览器，我们需要两个步骤：
* 通过response对象获取字节输出流：servletOutputStream outputStream =
resp.getOutputStream();
* 通过字节输出流写数据：outputStream。write(字节数据)；
1.返回一个图片文件到浏览器，如下： /** * 响应字节数据：设置字节数据的响应体 */ @WebServlet("/resp4") public
class ResponseDemo4 extends HttpServlet { @Override protected void doGet(
HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException { //1. 读取文件 FileInputStream fis = new
FileInputStream("d://a.jpg"); //2. 获取response字节输出流 ServletOutputStream os =
response.getOutputStream(); //3. 完成流的copy byte[] buff = new byte[1024]; int len
= 0; while ((len = fis.read(buff))!= -1){ os.write(buff,0,len); } fis.close(); }
@Override protected void doPost(HttpServletRequest request, HttpServletResponse
response) throws ServletException, IOException { this.doGet(request, response);
} }
上述代码中，对于流的copy的代码还是比较复杂的，所以我们可以使用别人提供好的方法来简化代码的开发，具体的步骤如下：
* pom.xml添加依赖 <dependency> <groupId>commons-io</groupId> <artifactId>commons-
io</artifactId> <version>2.6</version> </dependency>
* 调用工具类方法 //fis:输入流 //os:输出流 IOUtils.copy(fis,os);
优化代码之后：
/** * 响应字节数据：设置字节数据的响应体 */ @WebServlet("/resp4") public class ResponseDemo4
extends HttpServlet { @Override protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException { //1. 读取文件
FileInputStream fis = new FileInputStream("d://a.jpg"); //2. 获取response字节输出流
ServletOutputStream os = response.getOutputStream(); //3. 完成流的copy IOUtils.copy(
fis,os); fis.close(); } @Override protected void doPost(HttpServletRequest
request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response); } }