如何使用自定义过滤器在插件中获取博客帖子数据？

I am trying to get blog post data in a custom plugin but I couldn't. I get NULL value in var_dump line. Is there any chance to get global $post in custom plugin?

<?php 

class Plugin {

    public function __construct() {
        add_filter( 'filter_1', [ $this, 'function_1' ], 1, 2 );
        add_filter( 'filter_1', [ $this, 'function_2' ], 2, 2 );
    }

    public function register() {
        return apply_filters( 'filter_1', true, "xyz" );
    }

    public function function_1( $param1, $param2 ) {
        global $post;
        var_dump($post);

        return $param_1;
    }

    public function function_2( $param1, $param2 ) {
        return $param_1;
    }
}

$plugin = new Plugin;
$plugin->register();

I think you are looking for $_POST variable. This variable will be available globally after request: http://php.net/manual/en/reserved.variables.post.php

Finally I get a solution:

$request = "test";
$post = new \WP_Query( array( 'pagename' => $request ) );