I have a quite complex xsd file that describe some objects (it\'s not important, but it\'s the DATEX II standard) Do you know if there is an automatic way to create an html
The answer to this depends on the intended user base, how you want your users to access your forms, and the technology stack you have in place already or you're willing to deploy.
If your users are quality control analysts, and so the intent is to have them use that generated UI to manage test cases, then a handful of commercial tools have this ability. A quick search on Google for terms such as "generate ui forms from XSD to test web services" should give you on first page the major players in this space (I won't name names to avoid conflict of interests). There are differences in how vendors approach this, that have to do with the time it takes to generate these forms from large bodies of XML Schema, which in turn translate into different degrees of usability. Given what I see in DATEX, from a complexity perspective, you may have a hard time to find a free tool for this...
If your users are rather data entry specialists, then the above are not the tools you want them to use. Without knowing much about your environment (I see your java-ee tag, but still not clear how it would relate to this task), one model could be a combination of InfoPath with SharePoint; while the process to generate the form is not fully automatic, it comes close to that. It is XSD driven, in the sense that at design time you drag and drop XSD on a design form, that allows you to build some really nice UI. Follow their competition on your particular technology stack and you may have your answer. Or, you can go to this site that lists XForms implementations; IBM's form designer, much like InfoPath, can use XML Schema for design, etc.
If this is for developers to get some XML, another alternative might also be to go with an Excel based (or SharePoint lists) approach and generate XML from that data (you give away cost to acquire something to build specific to your requirements tooling, here assuming people that are really familiar with spreadsheets instead).
Given how DATEX model looks like, you'll have to do some manual customizations anyway, if you plan to use the extensibility model, or if you choose to build different forms for different scenarios i.e. instead of one big form that'll give you all descendents for the abstract payloadPublication in some drop down, to just a specific, simple form e.g. MeasurementSiteTablePublication.