# Redirect

## redirect重定向流程

參考資料:(<http://www.51gjie.com/javaweb/955.html>)

客戶發送一個請求到服務器，服務器匹配servlet，這都和請求轉發一樣，servlet處理完之後調用了sendRedirect()這個方法，這個方法是response的方法，所以，當這個servlet處理完之後，看到response. senRedirect()方法，立即向客戶端返回這個響應，響應行告訴客戶端你必須要再發送一個請求，去訪問test.jsp，緊接著客戶端受到這個請求後，立刻發出一個新的請求，去請求test.jsp,這裡兩個請求互不干擾，相互獨立，在前面request裡面setAttribute()的任何東西，在後面的request裡面都獲得不了。可見，在sendRedirect()裡面是兩個請求，兩個響應。

### response.sendRedirect重定向跳轉

```
@RequestMapping(value="/testredirect",method = { RequestMethod.POST, RequestMethod.GET })  
public ModelAndView testredirect(HttpServletResponse response){  
    response.sendRedirect("/index");
    return null; 
}
```

### ViewResolver直接跳轉

```
@RequestMapping(value="/testredirect",method = { RequestMethod.POST, RequestMethod.GET })  
public  String testredirect(HttpServletResponse response){  
    return "redirect:/index";  
} 
```

#### 帶參數

```
@RequestMapping("/testredirect")
public String testredirect(Model model, RedirectAttributes attr) {
    //跳轉地址帶上test參數
    attr.addFlashAttribute("test", "51gjie");
    //u2參數不會跟隨在URL後面
    attr.addFlashAttribute("u2", "51gjie");
	  return "redirect:/user/users";
}
```

### ModelAndView重定向

```
@RequestMapping(value="/restredirect",method = {RequestMethod.POST, RequestMethod.GET})  
public ModelAndView restredirect(String userName){  
    ModelAndView model = new ModelAndView("redirect:/main/index");    
    return model;  
}
```

#### 帶參數

```
@RequestMapping(value="/toredirect",method = {RequestMethod.POST, RequestMethod.GET})  
public ModelAndView toredirect(String userName){  
    ModelAndView model = new ModelAndView("/main/index");   
    //把userName參數帶入到控制器的RedirectAttributes
    model.addObject("userName", userName);  
    return model;  
}
```

### 總結

1\. redirect重定向可以跳轉到任意服務器，可以用在系統間的跳轉。

2\. Spring MVC中redirect重定向，參數傳遞可以直接拼接url也可以使用RedirectAttributes來處理，由於是不同的請求，重定向傳遞的參數會在地址欄顯示，所以傳遞時要對中文編碼進行處理。


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