【Java】使用Stream API处理Map并返回新的Map_java stream 返回map

import java.util.HashMap;
import java.util.Map;
import java.util.stream.Collectors;
 
public class Main {
    public static void main(String[] args) {
        // Create a HashMap to store the original key-value pairs
        Map<String, Object> originalMap = new HashMap<>();
        // Add some key-value pairs to the originalMap
        originalMap.put("key1", "Hello");
        originalMap.put("key2", 42);
        originalMap.put("key3", "World");
        originalMap.put("key4", 3.14);
 
        // Use Java Stream API to process the originalMap and create a new map
        Map<String, Object> newMap = originalMap.entrySet().stream()
                .collect(Collectors.toMap(
                        // Keep the original key for each entry
                        Map.Entry::getKey,
                        // Lambda function to process each entry
                        entry -> {
                            // Get the value of the current entry
                            Object value = entry.getValue();
                            // Check if the value is an instance of String
                            if (value instanceof String) {
                                // Perform some operation for String type values (e.g., convert to uppercase)
                                return ((String) value).toUpperCase();
                            } else {
                                // Perform some operation for non-String type values (e.g., convert to string and append "_converted")
                                return value.toString() + "_converted";
                            }
                        }
                ));
 
        // Print the original and new maps to the console
        System.out.println("Original Map: " + originalMap);
        System.out.println("New Map: " + newMap);
    }
}

使用entrySet()方法返回一个包含键值对的Set集合，然后转Stream并对其执行操作，接着在收集器collect当中对map的value做不同的处理并返回