如何解決這個IlleagalstateException在訪問部署在Tomcat上的restful spring-boot應用程序？

Question

我得到threw exception java.lang.IllegalStateException: getWriter() has already been called for this response at org.apache.catalina.connector.Response.getOutputStream(Response.java:544)

同時通過angular2傳遞我的服務器端代碼（RESTFul，Spring-boot）。兩者都部署在同一臺服務器上（Tomcat 8.0.2）。

下面是我的代碼

@RequestMapping(value="/login", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE) 
public User login() { 
    Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal(); 
    User user = (User) principal; 

    return user; 
} 

怎樣才能解決這個問題？

Answer 1

變化：

@RequestMapping(value="/login", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE) 
public User login(Principal principal) { 
    User user = (User) principal; // take care of the conversion! 
    return user; 
} 

或

@RequestMapping(value="/login", method = RequestMethod.POST, produces = MediaType.APPLICATION_JSON_VALUE) 
public User login(Authentication authentication) { 
    User user = (User) authentication.getPrincipal(); // take care of the conversion! 
    return user; 
}