This tutorial shows how to OCR an image and export the OCR results to a JSON file in a Java application using the LEADTOOLS SDK.
Overview | |
---|---|
Summary | This tutorial covers how to save OCR results to JSON in a Java application. |
Completion Time | 30 minutes |
Project | Download tutorial project (2 KB) |
Platform | Java Application |
IDE | Eclipse / IntelliJ |
Runtime License | Download LEADTOOLS |
Try it in another language |
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Get familiar with the basic steps of creating a project by reviewing the Add References and Set a License tutorial, before working on the Export OCR Results to JSON - Java tutorial.
Start with a copy of the project created in the Add References and Set a License tutorial. If that project is unavailable, follow the steps in that tutorial to create it.
The references needed depend upon the purpose of the project. References can be added by local .jar
files located at <INSTALL_DIR>\LEADTOOLS21\Bin\Java
.
For this project, the following references are needed:
gson.jar
leadtools.jar
leadtools.caching.jar
leadtools.codecs.jar
leadtools.document.jar
leadtools.document.writer.jar
leadtools.document.pdf.jar
leadtools.ocr.jar
leadtools.pdf.jar
leadtools.svg.jar
For a complete list of which JAR files are required for your application, refer to Files to be Included with your Java Application.
The License unlocks the features needed for the project. It must be set before any toolkit function is called. For details, including tutorials for different platforms, refer to Setting a Runtime License.
There are two types of runtime licenses:
Note
Adding LEADTOOLS local references and setting a license are covered in more detail in the Add References and Set a License tutorial.
With the project created, the references added, and the license set, coding can begin.
Open the _Main.java
class in the Project Explorer. Add the following statements to the import
block at the top.
import com.google.gson.*;
import java.io.File;
import java.io.IOException;
import java.nio.file.*;
import java.util.*;
import leadtools.*;
import leadtools.document.*;
import leadtools.ocr.*;
Inside the run()
method, add the following to set the library path to where the C DLL files are located, as well as load the LEADTOOLS libraries that were previously imported. Also, add two new String
values that will represent the input file and the directory to output the JSON to. For the purposes of this tutorial, the PDF in the following file path is used: <INSTALL_DIR>\LEADTOOLS21\Resources\Images\leadtools.pdf
public static void main(String[] args) throws IOException {
new _Main().run(args);
}
private void run(String[] args) {
try {
Platform.setLibPath("C:\\LEADTOOLS21\\Bin\\CDLL\\x64");
Platform.loadLibrary(LTLibrary.LEADTOOLS);
Platform.loadLibrary(LTLibrary.DOCUMENT);
Platform.loadLibrary(LTLibrary.DOCUMENT_WRITER);
Platform.loadLibrary(LTLibrary.OCR);
SetLicense();
String file = "C:\\LEADTOOLS21\\Resources\\Images\\leadtools.pdf";
String outputDirectory = "C:\\LEADTOOLS21\\Resources\\Images";
OcrEngine ocrEngine = InitOcrEngine();
OCRandSaveResults(ocrEngine, file, outputDirectory);
}
catch(Exception ex) {
System.err.println(ex.getMessage());
ex.printStackTrace();
}
}
Add a new method to the _Main
class called InitOcrEngine()
. Call this method inside the run()
method below the call to the SetLicense()
method and the setting of the String
values, as shown above. Add the below code to return the initialized OcrEngine
.
OcrEngine InitOcrEngine()
{
// Initialize OCR engine
OcrEngine ocrEngine = OcrEngineManager.createEngine(OcrEngineType.LEAD);
ocrEngine.startup(null, null, null, "C:\\LEADTOOLS21\\Bin\\Common\\OcrLEADRuntime");
return ocrEngine;
}
Add another method at the bottom of the _Main
class called OCRandSaveResults(OcrEngine ocrEngine, String file, String outputDirectory)
. Call the newly created method in the run()
method after the OcrEngine ocrEngine = InitOcrEngine();
line of code, as shown above.
void OCRandSaveResults(OcrEngine ocrEngine, String file, String outputDirectory) throws IOException
{
LoadDocumentOptions options = new LoadDocumentOptions();
options.setFirstPageNumber(1);
options.setLastPageNumber(-1);
LEADDocument document = DocumentFactory.loadFromFile(file, options);
document.getText().setOcrEngine(ocrEngine);
List<DocumentPageText> documentPageTexts = new ArrayList<DocumentPageText>();
for (DocumentPage page : document.getPages())
{
// Parse the text and build the DocumentPageText object
DocumentPageText pageText = page.getText();
pageText.buildText();
pageText.buildWords();
documentPageTexts.add(pageText);
}
// Get the filename and create the output directory
File fileWithoutExt = new File(file.substring(0, file.lastIndexOf(".")));
String fileName = fileWithoutExt.getName();
String outputDir = PathCombine(outputDirectory, fileName + "-results");
Files.createDirectory(Path.of(outputDir));
// Save the recognized words to JSON
Gson gson = new Gson();
var json = gson.toJson(documentPageTexts);
var jsonPath = PathCombine(outputDir, fileName + "-words.json");
Files.write(Path.of(jsonPath), json.getBytes());
}
Next, add a new method to the _Main
class called PathCombine(String... paths)
. This method will be called twice inside the OCRandSaveResults()
method, as shown above. Add the below code to combine the file paths and return the corresponding String
.
public String PathCombine(String... paths)
{
File file = new File(paths[0]);
for (int i = 1; i < paths.length ; i++) {
file = new File(file, paths[i]);
}
return file.getPath();
}
Run the project by pressing Ctrl + F11, or by selecting Run -> Run.
If the steps were followed correctly, the application will OCR the given document and create a JSON file containing the recognition results in the specified output directory.
Download the resulting JSON here.
This tutorial showed how to run OCR on a document and export the results to JSON. Also, it covered how to use the IOcrEngine
interface, along with the LEADDocument
, DocumentPage
and DocumentPageText
classes.