There are two main ways to get parameters in the spring MVC background control layer: one is request.getParameter("name"), the other is to get parameters directly with the annotation @ RequestParam. Here's the main comment
1, Basic use, get submitted parameters
Back end code:
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@RequestMapping(path = { "/list" }, method = RequestMethod.GET) public String listUser(@RequestParam(defaultValue = "1", required = false) Integer pageIndex, Model model,String keyWord, UserSerachEnum type, @RequestParam(defaultValue = "user", required = false) String folder) { .... }
Front end code:
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<tr> <td><img src='<c:url value="/upload/$.png"></c:url>' style="width: 100px; height: 100px"></td> <td>$</td> <td>$</td> <td><a href='<c:url value="/user/update?id=$"></c:url>'>modify</a>   <a href='<c:url value="/user/remove?id=$"></c:url>'>delete</a></td> </tr>
Front end interface:
Execution result:
test1
123
You can see that spring will automatically enter by encapsulating the parameter name. We can use the parameter name directly
2, Handling of various abnormal situations
1. You can specify a parameter name for the incoming parameter
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@RequestParam String inputStr // The following parameter is specified as aa. If the front end does not pass the aa parameter name, an error will be reported @RequestParam(value="aa") String inputStr
Error message:
HTTP Status 400 - Required String parameter 'aa' is not present
2. You can ask whether the front-end parameters configured by @ RequestParam must be passed through required=false or true
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// If required=false, the parameter will be given a value of null. If required=true, there must be @RequestMapping("testRequestParam") public String filesUpload(@RequestParam(value="aa", required=true) String inputStr, HttpServletRequest request)
3. If the parameter annotated with @ RequestMapping is of int basic type, but required=false, an error will be reported if the parameter value is not passed, because if the value is not passed, the value will be assigned as null to int, which is not allowed
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@RequestMapping("testRequestParam") public String filesUpload(@RequestParam(value="aa", required=true) String inputStr, @RequestParam(value="inputInt", required=false) int inputInt ,HttpServletRequest request) { // ... omitted return "index"; }