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Java 8: changing values ​​of stream EntrySet

I have the following setup:

Map<Instant, String> items;
...
String renderTags(String text) {
    // Renders markup tags in a string to human readable form
}
...
<?> getItems() {
    // Here is where I need help
}

My problem is that the strings that are map values items

are tagged. I want to be able to getItems()

return all elements, but with syntax strings using the method renderTags(String)

. Something like:

// Doesn't work
items.entrySet().stream().map(e -> e.setValue(renderTags(e.getValue())));

What's the most efficient way to do this?

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4 answers


If you want to get Map

:



Map<Instant, String> getItems() {
    return items.entrySet()
            .stream()
            .collect(Collectors.toMap(
                    Map.Entry::getKey,
                    e -> renderTags(e.getValue())));
}
+9


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If you want to modify an existing map instead of generating a new one (like in your example), there is no need to use this stream at all. Use Map.replaceAll

:

items.replaceAll((k, v) -> renderTags(v));
return items;


If you want to keep the original map intact, please refer to the other answers.

+7


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You can try this with Collectors.toMap()

:

Map<Instant, String> getItems() {
    return items.entrySet().stream()
                .collect(Collectors.toMap(
                            Map.Entry::getKey,
                            entry -> renderTags(entry.getValue())
                         ));
}

By the way, if the name just says "get", you shouldn't convert it at all. The getter can be expected to be simple and inexpensive.

+3


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An alternative could be

Map<Instant, String> getItems() {
return items.entrySet().stream()
           .peek(entry -> entry.setValue(renderTags(entry.getKey())))
           .collect(Collectors.toMap(Map.Entry::getKey,e -> e.getValue()));
}

Useful if you need to perform updates on the stream before calling the collector.

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