import org.junit.Test; import java.util.HashMap; import java.util.Map; public class FlatmapTest { @Test public void test() { Map<Integer, Map<String, Integer>> map = new HashMap<>(); Map<String, Integer> map1 = new HashMap<>(); map1.put(“a”, 1); map1.put(“b”, 2); map.put(1, map1); map1 = new HashMap<>(); map1.put(“c”, 3); map1.put(“d”, 4); map.put(2, map1); Integer sum = map.values().stream() .map(Map::values) .flatMap(i -> i.stream()) .reduce(0, Integer::sum); System.out.println(sum); […]

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Sometimes can be useful extract some specific attribute from a JSON string. This can be done easily with com.google.code.gson library in this way. Let’s consider the following JSON: This is the maven dependancy: And finally the code to extract the value of “field2”:

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If you find you are repeatedly using the same attributes with @Transactional on many different methods, then Spring’s meta-annotation support allows you to define custom shortcut annotations for your specific use cases. For example, defining the following annotations: allows us to write the example from the previous section as As you can see meta-annotations can […]

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