About the servlet response of sethead and addhead

response.sethead ("name", "liudehua1");
response.addhead ("name", "liudehua2");
response.sethead ("name", "liudehua3");

The third line of code , would have replaced the two previous name , or just replace one yet.
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to write a servlet to test the following .

URL url = new URL("http://localhost:8080/apps/Servlet/Test");
 		URLConnection uc = url.openConnection();
 		Map<String, List<String>> headers = uc.getHeaderFields();
 		System.out.println(headers);

glance .
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write their own code to try
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someone to help answer the following questions Why , thank you.
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setHeader will reset the value of the same key , if not new . addHeader will correspond to the same key value into an array.