How to filter out empty or null values using java 8?

Question

I have a parameter map and I am trying to build the complete url by appending the request parameters to the url.

Following code is what I have done so far to extract key values from the parameter map.

Map<String, String[]> parameters = request.getParameterMap();

String params = parameters.entrySet()
                .stream()
                .map(e -> e.getKey() + "=" + String.join(",", e.getValue()))
                .collect(Collectors.joining("&"));
String url = requestUrl + "?" + params;

My url currently prints something similar to following if I pass value only to the year parameter:

/student/query?Id=&grade=&year=2018

I want to print something like:

/student/query?year=2018

If I do not pass value for a certain parameter I do not want it to be printed.

How can I fix this?

You should [encode](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/URLEncoder.html#encode(java.lang.String,java.lang.String)) each key and value. — VGR, Sep 28 '18 at 14:50

xingbin · Accepted Answer · 2018-09-28T15:14:22.217

2

You can use filter which only keeps String[] that contains non-empty strings:

            .filter(e -> {
                String[] value = e.getValue();
                if (value == null || value.length == 0) {
                    return false;
                } else {
                    for (String element : value) {
                        if (element != null && !element.isEmpty()) {
                            return true;
                        }
                    }
                    return false;
                }
            })

edited Sep 28 '18 at 15:14

answered Sep 28 '18 at 14:49

xingbin

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I have tried this and it still prints the `/student/query?Id=&grade=&year=2018` – BlueStar Sep 28 '18 at 14:59
@BlueStar What is your input `parameters`? – xingbin Sep 28 '18 at 15:00
I can query a student on 3 parameters. Id, grade and year. If I just pass year as the parameter I want the value of my url variable to be `/student/query?year=2018` – BlueStar Sep 28 '18 at 15:03

How to filter out empty or null values using java 8?

1 Answers1