Replacing variables in a word document template with java

Yes, you can do it using Apache-POI. Your variable names must be unique. See the following code

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import org.apache.poi.hwpf.HWPFDocument;
import org.apache.poi.hwpf.usermodel.CharacterRun;
import org.apache.poi.hwpf.usermodel.Paragraph;
import org.apache.poi.hwpf.usermodel.Range;
import org.apache.poi.hwpf.usermodel.Section;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;

public class HWPFTest {
    public static void main(String[] args){
        String filePath = "F:\\Sample.doc";
        POIFSFileSystem fs = null;        
        try {            
            fs = new POIFSFileSystem(new FileInputStream(filePath));            
            HWPFDocument doc = new HWPFDocument(fs);
            doc = replaceText(doc, "$VAR", "MyValue1");
            saveWord(filePath, doc);
        }
        catch(FileNotFoundException e){
            e.printStackTrace();
        }
        catch(IOException e){
            e.printStackTrace();
        }
    }

    private static HWPFDocument replaceText(HWPFDocument doc, String findText, String replaceText){
        Range r1 = doc.getRange(); 

        for (int i = 0; i < r1.numSections(); ++i ) { 
            Section s = r1.getSection(i); 
            for (int x = 0; x < s.numParagraphs(); x++) { 
                Paragraph p = s.getParagraph(x); 
                for (int z = 0; z < p.numCharacterRuns(); z++) { 
                    CharacterRun run = p.getCharacterRun(z); 
                    String text = run.text();
                    if(text.contains(findText)) {
                        run.replaceText(findText, replaceText);
                    } 
                }
            }
        } 
        return doc;
    }

    private static void saveWord(String filePath, HWPFDocument doc) throws FileNotFoundException, IOException{
        FileOutputStream out = null;
        try{
            out = new FileOutputStream(filePath);
            doc.write(out);
        }
        finally{
            out.close();
        }
    }
}

Recently I had to solve the same problem but with a .docx document. And trying the approach above resulted as the following error (As reported in this post):

org.apache.poi.poifs.filesystem.OfficeXmlFileException: The supplied data appears to be in the Office 2007+ XML. You are calling the part of POI that deals with OLE2 Office Documents. You need to call a different part of POI to process this data (eg XSSF instead of HSSF)

Finally, I had to change the code as follow (in my case the .docx file is inside the resource folder):

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URISyntaxException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import org.apache.poi.xwpf.usermodel.XWPFDocument;

public class XWPFTest {

    public static void main(String[] args) throws URISyntaxException, IOException {
        String resourcePath = "template.docx";
        Path templatePath = Paths.get(XWPFTest.class.getClassLoader().getResource(resourcePath).toURI());
        XWPFDocument doc =  new XWPFDocument(Files.newInputStream(templatePath));
        doc = replaceTextFor(doc, "UNIQUE_VAR", "MyValue1");
        saveWord("C:\\document.docx", doc);
    }

    private static XWPFDocument replaceTextFor(XWPFDocument doc, String findText, String replaceText){
        doc.getParagraphs().forEach(p ->{
            p.getRuns().forEach(run -> {
                String text = run.text();
                if(text.contains(findText)) {
                    run.setText(text.replace(findText, replaceText), 0);
                } 
            });
        });

        return doc;
    }

    private static void saveWord(String filePath, XWPFDocument doc) throws FileNotFoundException, IOException{
        FileOutputStream out = null;
        try{
            out = new FileOutputStream(filePath);
            doc.write(out);
        }
        catch(Exception e) {
            e.printStackTrace();
        }
        finally{
            out.close();
        }
    }

}

P.S. I had to remove the $ because in .docx are managed are separate runs so I had to opt for the approach of a unique var name. I needed the following Apache POI dependencies:

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi</artifactId>
    <version>3.17</version>
</dependency>
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-ooxml</artifactId>
    <version>3.17</version>
</dependency>
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-scratchpad</artifactId>
    <version>3.17</version>
</dependency>