HTTPServletRequest getParameterMap() vs getParameterNames

Question

HTTPServletRequest req, has a method getParameterMap() but, the values return a String[] instead of String, for post data as

name=Marry&lastName=John&Age=20.

I see in the post data it's not an array, but getParameterMap() returns array for every key(name or lastName or Age). Any pointers on understanding this in a better way?

The code is available in Approach 2. Approach 1 works completely fine.

Approach 1:

Enumeration<String> parameterNames = req.getParameterNames();

while (parameterNames.hasMoreElements()) {
    String key = (String) parameterNames.nextElement();
    String val = req.getParameter(key);
    System.out.println("A= <" + key + "> Value<" + val + ">");
}

Approach 2:

Map<String, Object> allMap = req.getParameterMap();

for (String key : allMap.keySet()) {
    String[] strArr = (String[]) allMap.get(key);
    for (String val : strArr) {
        System.out.println("Str Array= " + val);
    }
}

score 22 · Accepted Answer · edited Feb 05 '19 at 11:52

22

If you are expecting pre determined parameters then you can use getParameter(java.lang.String name) method.

Otherwise, approaches given above can be used, but with some differences, in HTTP-request someone can send one or more parameters with the same name.

For example:

name=John, name=Joe, name=Mia

Approach 1 can be used only if you expect client sends only one parameter value for a name, rest of them will be ignored. In this example you can only read "John"

Approach 2 can be used if you expect more than one values with same name. Values will be populated as an array as you showed in the code. Hence you will be able to read all values, i.e "John","Joe","Mia" in this example

Documentation

edited Feb 05 '19 at 11:52

Mike

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answered Jan 01 '15 at 15:50

kamoor

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thanks, could you please explain with some post data example, suitable for approach 1 and 2? – NNikN Jan 01 '15 at 15:56
When I try the following url, I get 1 map member (key: r), and its an array with two elements [123123,98734]. https://localhost/app/faces/main.xhtml?r=123123&r=98734 – Harun Dec 07 '15 at 22:35
Often "lost"..is yes, you can (just fine) have ?myQueryStringNameOne=aaa&myQueryStringNameOne=bbb&myQueryStringNameOne=ccc – granadaCoder Dec 17 '20 at 00:42

HTTPServletRequest getParameterMap() vs getParameterNames

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