Question

如何将 2 个映射合并为一个具有集合值的映射

<?php
    include ('navbar.php');
?>
<form class = "container m-5" method = "POST" action = "upload.php" encytype = "multipart/form-data">
<input class = "form-control w-25" type = "file" name = "file">
<button class = "btn" type = "submit" name = "Upload">Upload</button>
</form>

<?php
include'connect.php';
$statusMsg = '';

// File upload path
$targetDir = "image";
$fileName = $_FILES["file"]["name"];
$targetFilePath = $targetDir . $fileName;
$fileType = pathinfo($targetFilePath,PATHINFO_EXTENSION);

if(isset($_POST["submit"]) && !empty($_FILES["file"]["name"])){
    // Allow certain file formats
    $allowTypes = array('jpg','png','jpeg','pdf');
    if(in_array($fileType, $allowTypes)){
        // Upload file to server
        if(move_uploaded_file($_FILES["file"]["tmp_name"], $targetFilePath)){
            // Insert image file name into database
            $insert = $db->query("INSERT into userid (FileName) VALUES ('".$fileName."'");
            if($insert){
                $statusMsg = "The file ".$fileName. " has been uploaded successfully.";
            }else{
                $statusMsg = "File upload failed, please try again.";
            } 
        }else{
            $statusMsg = "Sorry, there was an error uploading your file.";
        }
    }else{
        $statusMsg = 'Sorry, only JPG, JPEG, PNG, GIF, & PDF files are allowed to upload.';
    }
}else{
    $statusMsg = 'Please select a file to upload.'; 
}

// Display status message
echo $statusMsg;
?>

这种方式将覆盖该值

Answer 1

您可以像这样使用 merge() 方法。

Map<String, Collection<Integer>> map1 = Map.of(
    "a", List.of(0, 1),
    "b", List.of(10));
Map<String, Collection<Integer>> map2 = Map.of(
    "a", List.of(2, 3),
    "c", List.of(20));
Map<String, Collection<Integer>> map3 = new HashMap<>(map1);
for (Entry<String, Collection<Integer>> e : map2.entrySet())
    map3.merge(e.getKey(), e.getValue(), (v0, v1) -> {
        Collection<Integer> list = new ArrayList<>(v0);
        list.addAll(v1);
        return list;
    });
System.out.println(map3);

输出：

{a=[a0, a1, a2, a3], b=[b0], c=[c1]}

Answer 2

return Stream.concat(map1.entrySet().stream(), map2.entrySet().stream())
         .collect(Collectors.toMap(
               Map.Entry::getKey,
               Map.Entry::getValue,
               (ids1, ids2) -> {
                  final Set<Integer> merged = new HashSet<>(ids1);
                  merged.addAll(ids2);
                  return merged;
               }));

}

如何将 2 个映射合并为一个具有集合值的映射

2 个答案: