Maven 与运行环境：从“能编译”走到“能请求”

import java.util.*;
public class Main {
    record Range(int low, int high) {
        Range {
            if (low < 1 || low > high) throw new IllegalArgumentException("bad range");
        }
    }
    record Choice(String status, Integer version, int low, int high) {}
    static Choice select(List<Range> requirements, List<Integer> installed) {
        int low = 1, high = Integer.MAX_VALUE;
        for (Range r : requirements) {
            // 累积交集：下界只能上升，上界只能下降。
            low = Math.max(low, r.low());
            high = Math.min(high, r.high());
        }
        if (low > high) return new Choice("CONFLICT", null, low, high);
        Integer chosen = null;
        for (int version : installed) {
            if (version < 1) throw new IllegalArgumentException("bad installed version");
            // 扫描可行候选，保留最小值而不依赖输入顺序。
            if (version >= low && version <= high &&
                    (chosen == null || version < chosen)) chosen = version;
        }
        // 区分约束冲突和仅缺少已安装候选。
        return new Choice(chosen == null ? "NOT_INSTALLED" : "SELECTED", chosen, low, high);
    }
    static void eq(Object expected, Object actual) {
        if (!Objects.equals(expected, actual)) throw new AssertionError(actual);
    }
    public static void main(String[] args) {
        eq(new Choice("SELECTED",17,17,17), select(
            List.of(new Range(17,21),new Range(17,17)),List.of(21,11,17)));
        eq("CONFLICT", select(List.of(new Range(17,17),new Range(21,21)),List.of(17,21)).status());
        eq("NOT_INSTALLED", select(List.of(new Range(17,17)),List.of(11,21)).status());
        eq(Integer.valueOf(17), select(List.of(new Range(17,21)),List.of(21,17,17)).version());
        eq("NOT_INSTALLED", select(List.of(),List.of()).status());
        try { new Range(21,17); throw new AssertionError("invalid range"); }
        catch (IllegalArgumentException expected) {}
        System.out.println("PASS 6 toolchain constraint tests");
    }
}