The DeepL API is a language translation API that allows other computer programs to send texts and documents to DeepL's servers and receive high-quality translations. This opens a whole universe of opportunities for developers: any translation product you can imagine can now be built on top of DeepL's best-in-class translation technology.
The DeepL Java library offers a convenient way for applications written in Java to interact with the DeepL API. We intend to support all API functions with the library, though support for new features may be added to the library after they’re added to the API.
To use the DeepL Java Library, you'll need an API authentication key. To get a key, please create an account here. With a DeepL API Free account you can translate up to 500,000 characters/month for free.
Java 1.8 or later.
Add this dependency to your project's build file:
implementation "com.deepl.api:deepl-java:1.6.0"
Add this dependency to your project's POM:
<dependency>
<groupId>com.deepl.api</groupId>
<artifactId>deepl-java</artifactId>
<version>1.6.0</version>
</dependency>
Import the package and construct a Translator. The first argument is a string
containing your API authentication key as found in your
DeepL Pro Account.
Be careful not to expose your key, for example when sharing source code.
import com.deepl.api.*;
class Example {
Translator translator;
public Example() throws Exception {
String authKey = "f63c02c5-f056-..."; // Replace with your key
translator = new Translator(authKey);
TextResult result =
translator.translateText("Hello, world!", null, "fr");
System.out.println(result.getText()); // "Bonjour, le monde !"
}
}This example is for demonstration purposes only. In production code, the authentication key should not be hard-coded, but instead fetched from a configuration file or environment variable.
Translator accepts additional options, see Configuration
for more information.
To translate text, call translateText(). The first argument is a string
containing the text you want to translate, or an iterable of strings if you want
to translate multiple texts.
sourceLang and targetLang specify the source and target language codes
respectively. The sourceLang is optional, if it is null the source language
will be auto-detected.
Language codes are case-insensitive strings according to ISO 639-1, for
example 'de', 'fr', 'ja''. Some target languages also include the regional
variant according to ISO 3166-1, for example 'en-US', or 'pt-BR'. The full
list of supported languages is in the API documentation.
There are additional optional arguments to control translation, see Text translation options below.
translateText() returns a TextResult, or a List of TextResults
corresponding to your input text(s). TextResult has the following accessors:
getText()returns the translated text,getDetectedSourceLanguage()returns the detected source language code, andgetBilledCharacters()returns the number of characters billed for the text.
class Example { // Continuing class Example from above
public void textTranslationExamples() throws Exception {
// Translate text into a target language, in this case, French:
TextResult result =
translator.translateText("Hello, world!", null, "fr");
System.out.println(result.getText()); // "Bonjour, le monde !"
// Translate multiple texts into British English
List<TextResult> results =
translator.translateText(List.of("お元気ですか？", "¿Cómo estás?"),
null,
"en-GB");
System.out.println(results.get(0).getText()); // "How are you?"
System.out.println(results.get(0).getDetectedSourceLanguage()); // "ja" the language code for Japanese
System.out.println(results.get(0).getBilledCharacters()); // 7 - the number of characters in the source text "お元気ですか？"
System.out.println(results.get(1).getText()); // "How are you?"
System.out.println(results.get(1).getDetectedSourceLanguage()); // "es" the language code for Spanish
System.out.println(results.get(1).getBilledCharacters()); // 12 - the number of characters in the source text "¿Cómo estás?"
// Translate into German with less and more Formality:
System.out.println(translator.translateText("How are you?",
null,
"de",
new TextTranslationOptions().setFormality(
Formality.Less)).getText()); // 'Wie geht es dir?'
System.out.println(translator.translateText("How are you?",
null,
"de",
new TextTranslationOptions().setFormality(
Formality.More)).getText()); // 'Wie geht es Ihnen?'
}
}In addition to the input text(s) argument, a translateText() overload accepts
a TextTranslationOptions, with the following setters:
setSentenceSplittingMode(): specify how input text should be split into sentences, default:'on'.SentenceSplittingMode.All: input text will be split into sentences using both newlines and punctuation.SentenceSplittingMode.Off: input text will not be split into sentences. Use this for applications where each input text contains only one sentence.SentenceSplittingMode.NoNewlines: input text will be split into sentences using punctuation but not newlines.
setPreserveFormatting(): controls automatic-formatting-correction. Set toTrueto prevent automatic-correction of formatting, default:false.setFormality(): controls whether translations should lean toward informal or formal language. This option is only available for some target languages, see Listing available languages.Formality.Less: use informal language.Formality.More: use formal, more polite language.
setGlossary(): specifies a glossary to use with translation, as a string containing the glossary ID, or aGlossaryInfoobject (this object is returned by glossary lookup functions, for examplelistGlossaries()).setGlossaryId()is also available for backward-compatibility, accepting a string containing the glossary ID.
setContext(): specifies additional context to influence translations, that is not translated itself. Characters in thecontextparameter are not counted toward billing.
See the API documentation for more information and example usage.setTagHandling(): type of tags to parse before translation, options are"html"and"xml".
The following options are only used if setTagHandling() is set to 'xml':
setOutlineDetection(): specifyfalseto disable automatic tag detection, default istrue.setSplittingTags(): list of XML tags that should be used to split text into sentences. Tags may be specified as an array of strings (['tag1', 'tag2']), or a comma-separated list of strings ('tag1,tag2'). The default is an empty list.setNonSplittingTags(): list of XML tags that should not be used to split text into sentences. Format and default are the same as for splitting tags.setIgnoreTags(): list of XML tags that containing content that should not be translated. Format and default are the same as for splitting tags.
For a detailed explanation of the XML handling options, see the API documentation.
To translate documents, call translateDocument() File objects. The first and
second arguments correspond to the input and output files respectively.
Just as for the translateText() function, the sourceLang and
targetLang arguments specify the source and target language codes.
There are additional optional arguments to control translation, see Document translation options below.
class Example { // Continuing class Example from above
public void documentTranslationExamples() throws Exception {
// Translate a formal document from English to German
File inputFile = new File("/path/to/Instruction Manual.docx");
File outputFile = new File("/path/to/Bedienungsanleitung.docx");
try {
translator.translateDocument(inputFile, outputFile, "en", "de");
} catch (DocumentTranslationException exception) {
// If an error occurs during document translation after the document was
// already uploaded, a DocumentTranslationException is thrown. The
// document_handle property contains the document handle that may be used to
// later retrieve the document from the server, or contact DeepL support.
DocumentHandle handle = exception.getHandle();
System.out.printf(
"Error after uploading %s, document handle: id: %s key: %s",
exception.getMessage(),
handle.getDocumentId(),
handle.getDocumentKey());
}
}
}translateDocument() is a convenience function that wraps multiple API calls:
uploading, polling status until the translation is complete, and downloading. If
your application needs to execute these steps individually, you can instead use
the following functions directly:
translateDocumentUpload(),translateDocumentGetStatus()(ortranslateDocumentWaitUntilDone()), andtranslateDocumentDownload()
In addition to the input file, output file, sourceLang and targetLang
arguments, translateDocument() accepts an optional
DocumentTranslationOptions, with the following setters:
setFormality(): same as in Text translation options.setGlossary(): same as in Text translation options.setGlossaryId(): same as in Text translation options.
Glossaries allow you to customize your translations using user-defined terms. Multiple glossaries can be stored with your account, each with a user-specified name and a uniquely-assigned ID.
You can create a glossary with createGlossary() by passing your desired
glossary name, and a GlossaryEntries object specifying the terms to
store in the glossary.
Each glossary applies to a single source-target language pair. Note: Glossaries are only supported for some language pairs, see Listing available glossary languages for more information.
If successful, the glossary is created and stored with your DeepL account, and
a GlossaryInfo object is returned including the ID, name, languages and entry
count.
class Example { // Continuing class Example from above
public void createGlossaryExample() throws Exception {
// Create an English to German glossary with two terms:
GlossaryEntries entries = new GlossaryEntries() {{
put("artist", "Maler");
put("prize", "Gewinn");
}};
GlossaryInfo myGlossary =
translator.createGlossary("My glossary", "en", "de", entries);
System.out.printf("Created '%s' (%s) %s->%s containing %d entries\n",
myGlossary.getName(),
myGlossary.getGlossaryId(),
myGlossary.getSourceLang(),
myGlossary.getTargetLang(),
myGlossary.getEntryCount());
// Example: Created 'My glossary' (559192ed-8e23-...) en->de containing 2 entries
}
}To construct the GlossaryEntries, you can insert entries using typical Map
functions like put(). The fromTsv() function allows creating GlossaryEntries
from TSV data.
You can also create a glossary using a glossary downloaded from the DeepL
website by using createGlossaryFromCsv() with either a CSV file, or a string
containing the CSV data:
class Example { // Continuing class Example from above
public createGlossaryFromCsvExample() throws Exception {
File csvFile = new File("/path/to/glossary_file.csv");
GlossaryInfo myGlossary =
translator.createGlossaryFromCsv("My glossary",
"en",
"de",
csvFile);
}
}The API documentation explains the expected CSV format in detail.
Functions to get, list, and delete stored glossaries are also provided:
getGlossary()takes a glossary ID and returns aGlossaryInfoobject for a stored glossary, or throws an exception if no such glossary is found.listGlossaries()returns a list ofGlossaryInfoobjects corresponding to all of your stored glossaries.deleteGlossary()takes a glossary ID orGlossaryInfoobject and deletes the stored glossary from the server, or throws an exception if no such glossary is found.
class Example { // Continuing class Example from above
public getListDeleteGlossaryExamples() throws Exception {
// Retrieve a stored glossary using the ID
String glossaryId = "559192ed-8e23-...";
GlossaryInfo myGlossary = translator.getGlossary(glossaryId);
// Find and delete glossaries named 'Old glossary'
List<GlossaryInfo> glossaries = translator.listGlossaries();
for (GlossaryInfo glossary : glossaries) {
if (glossary.getName() == "Old glossary") {
translator.deleteGlossary(glossary);
}
}
}
}The GlossaryInfo object does not contain the glossary entries, but instead
only the number of entries in the entry_count property.
To list the entries contained within a stored glossary, use
getGlossaryEntries() providing either the GlossaryInfo object or glossary
ID:
class Example { // Continuing class Example from above
public getGlossaryEntriesExample() throws Exception {
GlossaryEntries entries = translator.getGlossaryEntries(myGlossary);
for (Map.Entry<String, String> entry : entries.entrySet()) {
System.out.println(entry.getKey() + ":" + entry.getValue());
}
// prints:
// artist:Maler
// prize:Gewinn
}
}You can use a stored glossary for text translation by setting the glossary
argument to either the glossary ID or GlossaryInfo object. You must also
specify the source_lang argument (it is required when using a glossary):
class Example { // Continuing class Example from above
public usingGlossaryExample() throws Exception {
String text = "The artist was awarded a prize.";
TextTranslationOptions options =
new TextTranslationOptions().setGlossary(my_glossary);
TextResult resultWithGlossary =
translator.translateText(text, "en", "de", options);
System.out.println(resultWithGlossary.getText()); // "Der Maler wurde mit einem Gewinn ausgezeichnet."
// For comparison, the result without a glossary:
TextResult resultWithoutGlossary =
translator.translateText(text, "en", "de");
System.out.println(resultWithoutGlossary.getText()); // "Der Künstler wurde mit einem Preis ausgezeichnet."
}
}Using a stored glossary for document translation is the same: set the glossary
argument and specify the source_lang argument:
class Example { // Continuing class Example from above
public getListDeleteGlossaryExamples() throws Exception {
String glossaryId = "559192ed-8e23-...";
DocumentTranslationOptions options =
new DocumentTranslationOptions().setGlossary(glossaryId);
File inputFile = new File("/path/to/Instruction Manual.docx");
File outputFile = new File("/path/to/Bedienungsanleitung.docx");
translator.translateDocument(inputFile,
outputFile,
"en",
"de",
options);
}
}The translateDocument() and translateDocumentUpload() functions both
support the glossary argument.
To check account usage, use the getUsage() function.
The returned Usage object contains three usage subtypes: character,
document and teamDocument. Depending on your account type, some usage
subtypes may be null. For API accounts:
usage.characteris non-null,usage.documentandusage.teamDocumentarenull.
Each usage subtype (if valid) has count and limit properties giving the
amount used and maximum amount respectively, and the limit_reached property
that checks if the usage has reached the limit. The top level Usage object has
the any_limit_reached property to check all usage subtypes.
class Example { // Continuing class Example from above
public void getUsageExample() throws Exception {
Usage usage = translator.getUsage();
if (usage.anyLimitReached()) {
System.out.println("Translation limit reached.");
}
if (usage.getCharacter() != null) {
System.out.printf("Character usage: %d of %d%n",
usage.getCharacter().getCount(),
usage.getCharacter().getLimit());
}
if (usage.getDocument() != null) {
System.out.printf("Document usage: %d of %d%n",
usage.getDocument().getCount(),
usage.getDocument().getLimit());
}
}
}You can request the list of languages supported by DeepL for text and documents
using the getSourceLanguages() and getTargetLanguages() functions. They both
return a list of Language objects.
The name property gives the name of the language in English, and the code
property gives the language code. The supportsFormality property only appears
for target languages, and indicates whether the target language supports the
optional formality parameter.
class Example { // Continuing class Example from above
public void getLanguagesExample() throws Exception {
List<Language> sourceLanguages = translator.getSourceLanguages();
List<Language> targetLanguages = translator.getTargetLanguages();
System.out.println("Source languages:");
for (Language language : sourceLanguages) {
System.out.printf("%s (%s)%n",
language.getName(),
language.getCode()); // Example: "German (de)"
}
System.out.println("Target languages:");
for (Language language : targetLanguages) {
if (language.getSupportsFormality()) {
System.out.printf("%s (%s) supports formality%n",
language.getName(),
language.getCode()); // Example: "Italian (it) supports formality"
} else {
System.out.printf("%s (%s)%n",
language.getName(),
language.getCode()); // Example: "Lithuanian (lt)"
}
}
}
}Glossaries are supported for a subset of language pairs. To retrieve those
languages use the getGlossaryLanguages() function, which returns an array
of GlossaryLanguagePair objects. Use the getSourceLanguage() and
getTargetLanguage() functions to check the pair of language codes supported.
class Example { // Continuing class Example from above
public void getGlossaryLanguagesExample() throws Exception {
List<GlossaryLanguagePair> glossaryLanguages =
translator.getGlossaryLanguages();
for (GlossaryLanguagePair glossaryLanguage : glossaryLanguages) {
System.out.printf("%s to %s\n",
glossaryLanguage.getSourceLanguage(),
glossaryLanguage.getTargetLanguage());
// Example: "en to de", "de to en", etc.
}
}
}You can also find the list of supported glossary language pairs in the API documentation.
Note that glossaries work for all target regional-variants: a glossary for the
target language English ("en") supports translations to both American English
("en-US") and British English ("en-GB").
All module functions may raise DeepLException or one of its subclasses. If
invalid arguments are provided, they may raise the standard exceptions
IllegalArgumentException.
If you use this library in an application, please identify the application with
TranslatorOptions.setAppInfo(), which takes the name and version of the app:
class Example { // Continuing class Example from above
public void configurationExample() throws Exception {
TranslatorOptions options =
new TranslatorOptions().setAppInfo("my-java-translation-plugin", "1.2.3");
Translator translator = new Translator(authKey, options);
}
}This information is passed along when the library makes calls to the DeepL API.
Both name and version are required. Please note that setting the User-Agent header
via TranslatorOptions.setHeaders() will override this setting, if you need to use this,
please manually identify your Application in the User-Agent header.
The Translator constructor accepts TranslatorOptions as a second argument,
for example:
class Example { // Continuing class Example from above
public void configurationExample() throws Exception {
TranslatorOptions options =
new TranslatorOptions().setMaxRetries(1).setTimeout(Duration.ofSeconds(
1));
Translator translator = new Translator(authKey, options);
}
}The available options setters are:
setMaxRetries(): maximum number of failed HTTP requests to retry, the default is 5. Note: only failures due to transient conditions are retried e.g. timeouts or temporary server overload.setTimeout(): connection timeout for each HTTP request.setProxy(): provide details about a proxy to use for all HTTP requests to DeepL.setHeaders(): additional HTTP headers to attach to all requests.setServerUrl(): base URL for DeepL API, may be overridden for testing purposes. By default, the correct DeepL API (Free or Pro) is automatically selected.
By default, we send some basic information about the platform the client library is running on with each request, see here for an explanation. This data is completely anonymous and only used to improve our product, not track any individual users. If you do not wish to send this data, you can opt-out when creating your Translator object by calling the setSendPlatformInfo() setter on the TranslatorOptions like so:
class Example { // Continuing class Example from above
public void configurationExample() throws Exception {
TranslatorOptions options =
new TranslatorOptions().setSendPlatformInfo(false);
Translator translator = new Translator(authKey, options);
}
}You can also customize the User-Agent header by setting its value explicitly in the TranslatorOptions object via the header field. Example:
class Example { // Continuing class Example from above
public void configurationExample() throws Exception {
Map<String, String> headers = new HashMap<>();
headers.put("User-Agent", "my custom user agent");
TranslatorOptions options =
new TranslatorOptions().setHeaders(headers);
Translator translator = new Translator(authKey, options);
}
}If you experience problems using the library, or would like to request a new feature, please open an issue.
We welcome Pull Requests, please read the contributing guidelines.
Execute the tests using ./gradlew test. The tests communicate with the DeepL
API using the auth key defined by the DEEPL_AUTH_KEY environment variable.
Be aware that the tests make DeepL API requests that contribute toward your API usage.
The test suite may instead be configured to communicate with the mock-server
provided by deepl-mock. Although most test cases work for either,
some test cases work only with the DeepL API or the mock-server and will be
otherwise skipped. The test cases that require the mock-server trigger server
errors and test the client error-handling. To execute the tests using
deepl-mock, run it in another terminal while executing the tests. Execute the
tests using ./gradlew test with the DEEPL_MOCK_SERVER_PORT and
DEEPL_SERVER_URL environment variables defined referring to the mock-server.