java

CII for Java: InvoiceXML API Examples

Java code samples for creating, validating, and parsing CII electronic invoices using the InvoiceXML API. Requires Java 15 or later (Java 17 or 21 LTS recommended): Create.java uses text blocks, which were introduced in Java 15. The other examples also compile on Java 8. Runs in Spring Boot, Quarkus, Micronaut, Jakarta EE, Android, AWS Lambda, or plain public static void main console apps.

For background on the CII syntax itself (what it is, when to use it standalone), see the main repository README.

Get your API key

Every example in this folder calls the InvoiceXML REST API. Sign up and generate a free API key here:

→ https://www.invoicexml.com/account/authentication

Pass it as a Bearer token on every request:

Authorization: Bearer YOUR_API_KEY

Important: set apiKey in the examples to the raw key only, without the Bearer prefix. If your account page shows the full header value (e.g. Bearer ixml_a1b2c3...), copy only the part after Bearer . The code adds the prefix itself when building the Authorization header.

Requirements

• Java 15 or later (Java 17 or 21 LTS recommended). Create.java uses text blocks, a Java 15+ feature; the other four examples also compile on Java 8.
• OkHttp 4.x for clean multipart handling and bearer auth

Maven

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.12.0</version>
</dependency>

Gradle

implementation 'com.squareup.okhttp3:okhttp:4.12.0'

OkHttp is the de facto standard HTTP client for modern Java. Java's built-in java.net.http.HttpClient does not support multipart out of the box, so doing this in pure JDK would triple the line count of every example.

Files in this folder

File	Operation	API endpoint
Create.java	Build a CII D16B XML invoice	POST /v1/create/cii
Validate.java	Validate a CII file against the D16B XSD and EN 16931 rules	POST /v1/validate/cii
ExtractJson.java	Parse a CII XML into JSON	POST /v1/extract/json
AiConvert.java	(Experimental) Convert a plain PDF to CII with AI	POST /v1/transform/to/cii
Render.java	Render CII XML into a human-readable PDF	POST /v1/render/cii/to/pdf

Each file is a standalone public class with a main method, runnable with javac and java directly, or as part of any Maven or Gradle project.

Note on the snippets below: they are excerpts from those files. The try blocks have no catch clause, so the enclosing method must declare throws Exception (or at least throws IOException), exactly as the full files do with public static void main(String[] args) throws Exception. Pasting a snippet into a method without that throws clause will not compile ("unreported exception IOException"). When in doubt, copy the complete file.

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Create a CII invoice in Java

String json = """
    {
      "invoice": {
        "invoiceNumber": "CII-2026-001",
        "issueDate": "2026-05-18",
        "currency": "EUR",
        "seller": {
          "name": "Acme GmbH",
          "vatIdentifier": "DE123456789",
          "legalRegistration": { "identifier": "HRB 12345" },
          "postalAddress": { "line1": "Hauptstraße 12", "city": "Berlin", "postCode": "10115", "country": "DE" }
        },
        "buyer": {
          "name": "Globex SAS",
          "postalAddress": { "line1": "15 rue de Rivoli", "city": "Paris", "postCode": "75001", "country": "FR" }
        },
        "paymentDetails": { "paymentAccountIdentifier": "DE89370400440532013000" },
        "lines": [{
          "quantity": 10,
          "priceDetails": { "netPrice": 150.00 },
          "vatInformation": { "rate": 19.00 },
          "item": { "name": "Senior consulting" }
        }]
      }
    }
    """;

RequestBody body = RequestBody.create(json, MediaType.parse("application/json"));

Request request = new Request.Builder()
    .url("https://api.invoicexml.com/v1/create/cii")
    .header("Authorization", "Bearer " + apiKey)
    .post(body)
    .build();

try (Response response = new OkHttpClient().newCall(request).execute()) {
    String xml = response.body().string();
    Files.write(Paths.get("invoice-cii.xml"), xml.getBytes("UTF-8"));
}

Totals and the VAT breakdown are calculated from the line items when omitted, and the document declares urn:cen.eu:en16931:2017 in BT-24.

The response is the CII D16B XML document, validated against the EN 16931 rules before delivery.

Full example: Create.java | API reference

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Validate a CII file in Java

RequestBody body = new MultipartBody.Builder()
    .setType(MultipartBody.FORM)
    .addFormDataPart("file", "invoice.xml",
        RequestBody.create(new File("invoice.xml"), MediaType.parse("application/xml")))
    .build();

Request request = new Request.Builder()
    .url("https://api.invoicexml.com/v1/validate/cii")
    .header("Authorization", "Bearer " + apiKey)
    .post(body)
    .build();

try (Response response = new OkHttpClient().newCall(request).execute()) {
    System.out.println(response.body().string());
}

Returns a JSON validation report listing any rule failures (EN 16931 BR-* and BR-CO-* rules).

Full example: Validate.java | API reference

---

Extract CII data as JSON in Java

Useful for feeding CII invoices into Spring Boot services, message queues, or any pipeline that prefers JSON over XML.

RequestBody body = new MultipartBody.Builder()
    .setType(MultipartBody.FORM)
    .addFormDataPart("file", "invoice.xml",
        RequestBody.create(new File("invoice.xml"), MediaType.parse("application/xml")))
    .build();

try (Response response = new OkHttpClient().newCall(
        new Request.Builder()
            .url("https://api.invoicexml.com/v1/extract/json")
            .header("Authorization", "Bearer " + apiKey)
            .post(body).build()
    ).execute()) {
    String json = response.body().string();
    // Deserialize with Jackson, Gson, or your preferred JSON library.
    // The invoice document sits under the "invoice" key: seller, buyer, lines, totals.
}

Full example: ExtractJson.java | API reference | Sample response

---

(Experimental) Convert a plain PDF to CII with AI

Experimental feature. Human verification required before any production use.

Real-world PDF invoices are often messy: scanned at low quality, irregularly formatted, multi-page, or missing fields that EN 16931 requires. AI extraction can make subtle mistakes that automated validators may not catch: wrong tax category codes, transposed amounts, missing seller VAT identifiers, incorrect currency formatting.

Always review the output before sending it to a customer or tax authority. See the AI conversion notes in the main README.

The endpoint takes the PDF alone; no extra parameters are needed.

Full example: AiConvert.java | API reference

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Render CII as a readable PDF in Java

CII is a machine format with no visual layer, so nobody can read it without tooling. This endpoint renders the XML into a formatted PDF preview, generated fresh from the structured data rather than extracted from any existing PDF layer, which makes it a quick way to eyeball what your XML actually says. The PDF is for reading only; the XML file remains the authoritative invoice for compliance and tax purposes.

RequestBody body = new MultipartBody.Builder()
    .setType(MultipartBody.FORM)
    .addFormDataPart("file", "invoice.xml",
        RequestBody.create(new File("invoice.xml"), MediaType.parse("application/xml")))
    .addFormDataPart("language", "en")   // en, de, or fr
    .build();

Request request = new Request.Builder()
    .url("https://api.invoicexml.com/v1/render/cii/to/pdf")
    .header("Authorization", "Bearer " + apiKey)
    .post(body)
    .build();

try (Response response = new OkHttpClient().newCall(request).execute()) {
    Files.write(Paths.get("invoice-preview.pdf"), response.body().bytes());
}

Full example: Render.java | API reference

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Framework integration

Spring Boot

Return a CII invoice from a REST controller:

@RestController
public class CIIController {

    @GetMapping(value = "/invoices/{id}/cii", produces = MediaType.APPLICATION_PDF_VALUE)
    public ResponseEntity<byte[]> download(@PathVariable String id) throws Exception {
        byte[] pdf = ciiService.create(id);
        return ResponseEntity.ok()
            .header("Content-Disposition", "attachment; filename=\"invoice-" + id + ".pdf\"")
            .body(pdf);
    }
}

Inject the API key from application.properties via @Value("${invoicexml.api-key}").

Quarkus

@Path("/invoices")
public class CIIResource {

    @GET
    @Path("/{id}/cii")
    @Produces("application/pdf")
    public Response download(@PathParam("id") String id) throws Exception {
        byte[] pdf = ciiService.create(id);
        return Response.ok(pdf)
            .header("Content-Disposition", "attachment; filename=\"invoice-" + id + ".pdf\"")
            .build();
    }
}

Android

OkHttp is also Square's library for Android, so the examples run on Android 5.0+ unchanged. Move the call off the main thread using enqueue(), CoroutineScope, or RxJava. For Android 9+ ensure your network security config allows TLS to api.invoicexml.com (it does by default).

AWS Lambda

Bundle OkHttp into your Lambda deployment package or layer. Cold-start latency is minimal because OkHttp is small (~700 KB).

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Common issues

• HTTP 401 Unauthorized: API key missing or invalid. Generate one at invoicexml.com/account/authentication and confirm you are sending Authorization: Bearer YOUR_API_KEY. A frequent cause: pasting the whole Bearer xxx value as apiKey, which sends Bearer Bearer xxx. Set apiKey to the raw key only.
• HTTP 400 Bad Request on Create: a required field is missing or malformed. Frequent causes: IssueDate not in ISO format (YYYY-MM-DD), Currency not in ISO 4217 (EUR, USD), country codes not in ISO 3166-1 alpha-2 (DE, FR).
• RequestBody.create() argument order: OkHttp 4.x reversed the parameter order from 3.x. Use RequestBody.create(File, MediaType) for 4.x. The 3.x signature (MediaType, File) is deprecated but still callable.
• Files.writeString not found: that method requires Java 11+. The examples use Files.write(Path, byte[]) which works on Java 8+.
• TLS handshake failures on old JDKs: enable TLS 1.2 explicitly on Java 8 with -Dhttps.protocols=TLSv1.2,TLSv1.3, or upgrade to Java 11+.
• Schematron BR-CO- failures on Validate*: line totals do not match the header total, or tax category and tax percentage are inconsistent. Recompute totals before posting.

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Resources

• Get an InvoiceXML API key
• Create CII API reference
• Validate CII API reference
• Extract JSON API reference
• Extract XML API reference
• Transform to CII API reference
• OkHttp documentation
• Main repository README