我在php上发送json编码的对象；
在php上，我首先处理对象的简单字段（int、string、data），一切正常。
当我尝试获取数组字段时，我使用“}”而不是[1,2，…n]（如果我在硬代码数据上尝试php，一切都正常）
我的类（java）1）

public class Sight {
    public Sight() {
        this.id = -1;
        this.name = "";
        this.photo = "";
        this.info = "";
        this.area_id = -1;
        this.area = "";
        this.update_date = new Date();
        this.coordinates = "";
        this.categoryId = -1;
        this.category = "";
        this.other_categories = new ArrayList<>();
        this.tags_values = new ArrayList<>();
        this.rate = -1;
    }

    @Expose
    @SerializedName("object_id")
    private int id;
    @Expose
    @SerializedName("name")
    private String name;
    @Expose
    @SerializedName("photo")
    private String photo;
    @Expose
    @SerializedName("info")
    private String info;
    @Expose
    @SerializedName("area_id")
    private int area_id;
    @Expose
    @SerializedName("area_name")
    private String area;
    @Expose
    @SerializedName("update_date")
    private Date update_date;
    @Expose
    @SerializedName("coordinates")
    private String coordinates;
    @Expose
    @SerializedName("category_id")
    private int categoryId;
    @Expose
    @SerializedName("category_name")
    private String category;
    @Expose
    @SerializedName("other_categories")
    public List<Integer> other_categories;
    @Expose
    @SerializedName("tags_values")
    public List<Integer> tags_values;
    @Expose
    @SerializedName("success")
    private Boolean success;
    @Expose
    @SerializedName("message")
    private String message;
    @Expose
    @SerializedName("rate")
    private int rate;
}

php代码：

<?php
    require_once "conn.php";
    $result =  array();

    $content = trim(file_get_contents("php://input"));
    $input = json_decode($content , true);

    //this lines only for debug!!! --->

      //to get json code of php-object
    array_push($result, json_encode($input));

      // to get array
    $temp = $content['other_categories'];
    array_push($result, json_encode($temp));

        //to get decoded array
    $temp = json_decode($content['other_categories'] , true);
    array_push($result, json_encode($temp));

    //these lines only for debag!! ---<

    $newname = $connection->real_escape_string($input['name']);
    $description = $connection->real_escape_string($input['info']);
    $area_id = $connection->real_escape_string($input['area_id']);
    $category_id = $connection->real_escape_string($input['category_id']);
    $tags = $connection->real_escape_string($input['tags_values']);
    $other_categories= $connection->real_escape_string($input['other_categories']);
    $photo = $connection->real_escape_string($input['photo']);
    $coordinates = $connection->real_escape_string($input['coordinates']);

    $query_insert_object =  "INSERT INTO `object`(`name`, `photo`, `info`, `area_id`, `update_date`, `coordinates`)
    VALUES ('$newname', '$photo', '$description', $area_id, NOW(), '$coordinates')";

    $query_id = "SELECT object_id FROM object ORDER BY object_id DESC LIMIT 1";
    if ($res = mysqli_query($connection, $query_insert_object)){

         $temp = mysqli_query($connection, $query_id);
         $id = mysqli_fetch_assoc($temp)['object_id'];
         $query_insert_main_category = "INSERT INTO `category_of_object`(`object_id`, `category_id`, `main`)
         VALUES ('$id','$category_id',1)";
         if ($res1 = mysqli_query($connection, $query_insert_main_category)){

             //code exactly go here, but cicles for and foreach never run ( $other_categories = null and $tags = null )
            for ($i = 1; $i < count($other_categories); $i++){

                $value=$other_categories[$i];
                 array_push($result, $value);
                $query_insert_other_categories = "INSERT INTO `category_of_object`(`object_id`, `category_id`, `main`)
                   VALUES ($id, $value ,0)";
                 if(!($res2 = mysqli_query($connection, $query_insert_other_categories)))
                 {
                     array_push($result, mysqli_error($connection));
                     echo "categories";
                 };

            }
            foreach ($tags as $value) {
                array_push($result, $value);
                 $query_insert_tags = "INSERT INTO `various_of_objects`(`various_of_characteristic_id`, `object_id`)
                 VALUES ('$value','$id')";

                 if (!($res3 = mysqli_query($connection, $query_insert_tags)))
                 {
                     array_push($result, mysqli_error($connection));
                     //echo "tags";
                 };
            }

            // Any of there line below I don't have in result! And all queries work fine on hard code data.
        } else{
            array_push($result, mysqli_error($connection));
            //echo "category";
            }
    } else {
        array_push($result, mysqli_error($connection));
       // echo "object";
    }

     echo json_encode($result);
    mysqli_close($connection);
?>

3/你怎么看，我在结果里放了一些数据进行调试。这是我的结果（来自php），result.size（）=3:php对象：（array_push（$result，json_encode（$input））；）

result[0] = 
"{"area_name":"",
"area_id":12,
"category_name":"",
"category_id":1,
"coordinates":"50, 60",
"object_id":-1,"info":"",
"name":"ewdfew",
"other_categories":[2,3,4,5],
"photo":"ewdfew 2511.7730756090899.jpg",
"rate":-1,
"tags_values":[1],
"update_date":"Dec 5, 2020 11:46:49 PM"}"

如您所见，有几个字段是空的，但我不使用它们！我需要数组，其他的类别和标签
数组(

array_push($result, json_encode($temp));
           $temp = json_decode($content['other_categories'] , true);
           array_push($result, json_encode($temp));:

和结果

result[1] = ""{""
result[2] = "null"

我用“{”代替数组。
非常感谢您的建议！我真的需要帮助。