1.由于浏览器的同源策略，前后端分离的时候会出现跨域的问题。
java 的解决方案是：
手写一个corsFilter 实现 Filter . 然后在 doFilter 方法中定义：
笔者用的springboot ，其他架构可能配置方式有所不同

@Component
@ServletComponentScan
@WebFilter(urlPatterns = "/*",filterName = "CorsFilter")
public class CorsFilter implements Filter {
	
	private static Logger log = Logger.getLogger(CorsFilter.class);
	
	@Value("${curvar}")
	private String curvar;


    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    	log.info("添加自定义注解 {}" +curvar);
    	System.out.print("添加自定义注解" + curvar);
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
    		throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) servletResponse;

		//跨域
        response.setHeader("Access-Control-Allow-Origin", "*");
		//跨域 Header
        response.setHeader("Access-Control-Allow-Methods", "*");
        response.setHeader("Access-Control-Allow-Headers", "Content-Type,XFILENAME,XFILECATEGORY,XFILESIZE");
        filterChain.doFilter(servletRequest, servletResponse);
    }

    @Override
    public void destroy() {

    }

}

前端的调用不受影响：

--------------------------------------- JS代码开始-------------------------------------------------------------------

$("#btnButton").click(function () {
	var userName=$('#userName').val();  
    var password=$('#password').val();  
    var age=$('#age').val();  
	var email=$('#email').val();  
    var userbean={userName:userName,password:password,age:age,email:email};
 console.log(userbean);	
    //Ajax调用处理
	$.ajax({  
        type: "POST",  
        contentType : "application/json ; charset=utf-8",  
        url:"http://127.0.0.1:8080/user/addUser",  
        data:JSON.stringify(userbean),  
        dataType: "json",  
        async: false,  
        success:function(data){  
            alert("..");  
        }  
     });  
});

--------------------------------------- JS代码结束-------------------------------------------------------------------

唯一要注意的是 data需要 转成 json

data:JSON.stringify(userbean);