Could not convert value of type "java.lang.String" to required type

Im executing the following code will display an error message. How do I resolve this error?

 @RequestMapping(value = "/Testresult", method = RequestMethod.POST)
    @ResponseBody
    public String testresult(
            HttpServletRequest request,
            @Valid TestCustomer<Customer> req
               ,BindingResult resultMsg) 
     {
        String content = "";
        if(resultMsg.hasFieldErrors() ){
            System.out.println("the error counts:" + resultMsg.getErrorCount());

        }
        return resultMsg.getErrorCount;
    }

//TestCustomer.java

public class TestCustomer<T> extends BaseUser {

    @Valid
    private T req;

    public T getReq() {
        return req;
    }

    public void setReq(T req) {
        this.req = req;
    }

}

//BaseUser.java
public class BaseUser {

    @Size(min=3, max=20)
    private String app;

    public String getApp() {
        return app;
    }

    public void setApp(String app) {
        this.app = app;
    }
}
//Customer.java
public class Customer implements Serializable{

    @Size(min=3, max=4)
    private String cust_id;

    private String order_id;

    public String getCust_id() {
        return cust_id;
    }

    public void setCust_id(String cust_id) {
        this.cust_id = cust_id;
    }

    public String getOrder_id() {
        return order_id;
    }

    public void setOrder_id(String order_id) {
        this.order_id = order_id;
    }
}

      

        
        
        
      

    

I am posting the following url

http: // localhost: 8080 / jd / order / Testresult? app = 122 & req = {\ "cust_id \": \ "\", \ "order_id \": \ "122 \"}

Firefox poster error:

/ * ["timestamp": 1436514495544, "status": 500, "error": "Internal server error", "exception": "org.springframework.beans.ConversionNotSupportedException", "message": "Unable to convert value of type" java.lang.String "to the required type" cn.vcredit.jd.emergencymoney.restservice.TestCustomer "; nested exception is java.lang.IllegalStateException: Cannot convert value of type [java.lang.String] to required type [cn.vcredit .jd.emergencymoney.restservice.TestCustomer]: no matching editors found or conversion strategy "] * /