试图通过resquest对象获取前端请求键值对，即request.getParamMap()
本来代码如下：
Map<String,String> map=request.getParamMap();
Map<String,String> map= request.getParameterMap(); Set<String> set=map.keySet(); Iterator<String> it=set.iterator(); while(it.hasNext()) { String next= it.next(); System.out.println("key:"+next+"->value:"+map.get(next)); } 然而报错，这是为什么呢？看源码，map来自request对象，查看源码即可知道：
/** Returns a java.util.Map of the parameters of this request. * Request parameters * are extra information sent with the request. For HTTP servlets, * parameters are contained in the query string or posted form data. * * @return an immutable java.util.Map containing parameter names as * keys and parameter values as map values. The keys in the parameter * map are of type String. The values in the parameter map are of type * String array. * */返回一个request的请求参数map
重点看划线部分的of type String ，of type String array
就是说key是String
value是String[]
解决后代码：
Map<String,String[]> map= request.getParameterMap(); Set<String> set=map.keySet(); Iterator<String> it=set.iterator(); while(it.hasNext()) { String next= it.next(); System.out.println("key:"+next+"->"); for(String s:map.get(next)) { System.out.println("value:"+s); }}
运行结果就正常了，
这告诉我们，多看源码，抠单词
