<?php

function getConnection() {
    $connection = false;
    $uri = 'mongodb://rwuser:1234567a@10.66.148.142:27017/admin?authMechanism=MONGODB-CR';
    $maxRetries = 5;
    for( $counts = 1; $counts <= $maxRetries; $counts++ ) {
        try {
            $connection = new MongoClient($uri);
        } catch( Exception $e ) {
     // 或者 根据需要使用下面的catch代码行，注意那一个“\\”，某些框架使用命名空间时需要用到。
     // } catch( \\Exception $e ) {
            continue;
        }
        break;
    }
    return $connection;
}

$connection = getConnection();

if($connection) {
        $db = $connection->testdb;
        $collection = $db->testcollection;

        $one = $collection->findOne();

        var_dump($one);
}