Day17
Example: Statistics of the number of visits
Create a variable of type int and save it in the ServletContext domain, so that all servlets can access it
Thought:
Initially there is no attribute in ServletCOntext to save the amount of visits
On the first access, create a variable, set the value to 1, and save it in the ServletContext
When accessed later, fetched from it, the value is incremented by 1.
//Steps: Get it first, and make a judgment based on the obtained value. If it is empty, it is the first access, and it will be created directly. If it is not empty, add 1 and then store it.
ServletContext context = this.getServletContext();
Integer count = (Integer)context.getAttribute("count");
if(count==null){
context.setAttribute("count", 1);
}
else {
count+=1;
context.setAttribute("count", count);
}
PrintWriter pw = response .getWriter ();
pw.print(count);
}
Get resources on the classpath: For a javaweb project, the classpath is /WEN-INF/CLASS
and /WEB-INF/lib every jar package!
// get ClassLoader
ClassLoader loader = this.getClass().getClassLoader();
// call the method
InputStream input = loader.getResourceAsStream("index.jap");
// Read the input stream content and convert it to a string
String s = IOUtils.toString(input);
System.out.println(s);
Response
Type is HttpServletResponse
setError(int sc)--à send error status code, such as 404 500
setError(int sc,String info) send error status code and add error message
setStatus(int sc)-à send the correct status code
response header
The response header is a key-value pair that can have multiple values of one name
setHeader(String name, String value) is used for single-value response headers,
For example: response .setHeader( "sss" , "SSS" );
addHeader(Stringname , String value), multi-valued response header (less used)
setIntHeader(Stringname , String value)
Response headers of type int for a single value
setDataHerder(Stringname , long value)
Response headers of type milliseconds for a single value
Response headers are automatically refreshed
PrintWriter writer = response.getWriter();
writer.print("huangying");
response.setHeader("Refresh","5;URL=/java10_1/Cservlet");
|
refresh time, jump address |
|
keywords |
Disable browser caching
Three sentences:
response.setHeader("Cache-Control", "no-cache");
response.setHeader("pargam", "no-cache");
response.setDateHeader("expires", -1);
response has two streams
ServletOutputStream: used to send byte data to the client
ServletOutputSteam out = response.getOutputStream();
Print Writer: used to send character data to the client! Need to set encoding
PrintWriter writer = response.getWriter();
cannot be used at the same time
Read an image into a byte array
String path = " image absolute path " ;
FileInputStream in = new FileInputStream(path);
byte[] bytes = IOUtils.toString(path);
response.getOutputStream().write(bytes);
|
Request uri: project name + servlet path |
redirect
response.sendRedirect("http://www.baidu.com");
request
Encapsulates all client request data
Get common information:
Get client IP
String request.getRemoteAddr();
Get request method:
Request.getMethod(); The return value is get or post deflation to call the do method
Get request headers:
String getHeader(String name); for single-value headers
Int getIntHeader(String name); applies to request headers of type int
Long getDateHeader(String name); applies to request headers of single-value millisecond type
Enumeration<String>getHeader(String name), suitable for multi-value request headers
// get client IP
String ip = request.getRemoteAddr();
System.out.println(ip);
// get request method
String mothod = request.getMethod();
System.out.println(mothod);
// Get client segment information
String user = request.getHeader("User-Agent");
System.out.println(user);
Get request URL:
String getScheme (); Get the protocol name
String getServerName(); Get the server name
String getServlerPort (); Get the server port number
String getContextPath (); Get the project address
String getServletPath (); Get the servlet address
String getQueryString (); get parameters
String getRequestURI (); get uri
String getRequestURL(); Get the request URL
Use referer request header to prevent anti-leech
If it is a local request, it will run to Baidu normally, otherwise it will go to index.jsp
String str = request.getHeader("Referer");
System.out.println(str);
if(!str.contains("localhost")||str==null){
response.sendRedirect("index.jsp");
}
else{
response.sendRedirect("http://www.baidu.com");
}
}
request request parameters
getparameter(parameter name); returns the value of the parameter
String[] name =request.getparamentValue(parameter name); if a parameter corresponds to multiple values, such as a check box
Enumeration names =request.getParamentNames(); returns all parameter names, which is an array
Map<String,String[]> map =request.getParamentMap();, get all request parameters, in the encapsulated map