Improve if-statement for multiple strings
i assume that you don't want to proceed the request, and send error message about missing string  to the user, and also you are not using any MVC framework.

First you need to define a list of parameter names.  Then define the below method,

 List&lt;String&gt; paramNames =  ... // you prepared a list of parameter names

List&lt;String&gt; validate(HttpServletRequest req ) {
   List&lt;String&gt; emptyParams = new ArrayList&lt;&gt;();

   for(String name : paramNames ){
      if(StringUtils.isBlank( req.getParameter(name))){
          emptyParams.add(param);
       }
   }

   return emptyParams;  
 }


Note: StringUtils class comes from the apache common library. 

now the above method can tell you what parameters are empty. you can decide what to do based on the result.  

if you use any mvc framework,  it is better to use form binding logic and validation provided by the framework.