Generate Document from JSON Data Source Leave feedback

Overview

GroupDocs.Assembly for Java enables you to generate documents directly from JSON data sources. The JsonDataSource class automatically parses JSON and makes it available to your templates, supporting both simple and complex JSON structures.

The main classes involved are:

JsonDataSource - loads and parses JSON data
DocumentAssembler - assembles documents from templates
DataSourceInfo - wraps the data source

Here are the steps to generate documents from JSON:

Create or obtain JSON data (from file, API, or string)
Instantiate JsonDataSource with the JSON data
Create a template document with expression tags referencing JSON properties
Use DocumentAssembler to assemble the template with JsonDataSource
Save the assembled document

Note
JsonDataSource automatically recognizes JSON types (numbers, booleans, dates, strings) and makes them available with proper types in templates, enabling numeric operations and date formatting.

Generate Document from JSON File

The simplest way to use JSON data is from a file:

import com.groupdocs.assembly.*;

public static void generateFromJsonFile() throws Exception
{
    JsonDataSource jsonDataSource = new JsonDataSource("data.json");

    DocumentAssembler assembler = new DocumentAssembler();
    assembler.assembleDocument("Template.docx", "Output.docx",
        new DataSourceInfo(jsonDataSource, "data"));
}

Generate Document from JSON String

The String parameter of the JsonDataSource constructor is a file path. To use JSON content held in a string, wrap it into an InputStream:

import com.groupdocs.assembly.*;
import java.io.*;
import java.nio.charset.StandardCharsets;

public static void generateFromJsonString() throws Exception
{
    String jsonString = "{"
        + "\"name\": \"John Doe\","
        + "\"age\": 30,"
        + "\"email\": \"john.doe@example.com\","
        + "\"active\": true"
        + "}";

    try (InputStream jsonStream = new ByteArrayInputStream(jsonString.getBytes(StandardCharsets.UTF_8)))
    {
        JsonDataSource jsonDataSource = new JsonDataSource(jsonStream);

        DocumentAssembler assembler = new DocumentAssembler();
        assembler.assembleDocument("Template.docx", "Output.docx",
            new DataSourceInfo(jsonDataSource, "person"));
    }
}

Working with JSON Arrays

When your JSON root is an array, JsonDataSource treats it as a collection:

import com.groupdocs.assembly.*;
import java.io.*;
import java.nio.charset.StandardCharsets;

public static void generateFromJsonArray() throws Exception
{
    String jsonArray = "["
        + "{ \"name\": \"John\", \"age\": 30 },"
        + "{ \"name\": \"Jane\", \"age\": 28 },"
        + "{ \"name\": \"Bob\", \"age\": 35 }"
        + "]";

    try (InputStream jsonStream = new ByteArrayInputStream(jsonArray.getBytes(StandardCharsets.UTF_8)))
    {
        JsonDataSource jsonDataSource = new JsonDataSource(jsonStream);

        DocumentAssembler assembler = new DocumentAssembler();
        assembler.assembleDocument("Template.docx", "Output.docx",
            new DataSourceInfo(jsonDataSource, "people"));
    }
}

Template Example for JSON Object

For a JSON object like {"name": "John", "age": 30}, your template can reference properties directly:

Name: <<[data.name]>>
Age: <<[data.age]>>

Template Example for JSON Array

For a JSON array, use a foreach data band to iterate:

<<foreach [in people]>>
Name: <<[name]>>, Age: <<[age]>>
<</foreach>>

Working with Nested JSON Objects

JsonDataSource handles nested JSON structures automatically:

import com.groupdocs.assembly.*;
import java.io.*;
import java.nio.charset.StandardCharsets;

public static void generateFromNestedJson() throws Exception
{
    String nestedJson = "{"
        + "\"company\": \"ABC Corp\","
        + "\"address\": {"
        + "    \"street\": \"123 Main St\","
        + "    \"city\": \"New York\","
        + "    \"zip\": \"10001\""
        + "},"
        + "\"employees\": ["
        + "    { \"name\": \"John\", \"position\": \"Developer\" },"
        + "    { \"name\": \"Jane\", \"position\": \"Manager\" }"
        + "]"
        + "}";

    try (InputStream jsonStream = new ByteArrayInputStream(nestedJson.getBytes(StandardCharsets.UTF_8)))
    {
        JsonDataSource jsonDataSource = new JsonDataSource(jsonStream);

        DocumentAssembler assembler = new DocumentAssembler();
        assembler.assembleDocument("Template.docx", "Output.docx",
            new DataSourceInfo(jsonDataSource, "company"));
    }
}

Template for nested JSON:

Company: <<[company.company]>>
Address: <<[company.address.street]>>, <<[company.address.city]>> <<[company.address.zip]>>

Employees:
<<foreach [in company.employees]>>
- <<[name]>>, <<[position]>>
<</foreach>>

Configure JSON Data Load Options

You can configure how JsonDataSource parses JSON:

import com.groupdocs.assembly.*;

public static void generateWithJsonOptions() throws Exception
{
    JsonDataLoadOptions options = new JsonDataLoadOptions();
    options.setAlwaysGenerateRootObject(true); // Always create root object
    options.setSimpleValueParseMode(JsonSimpleValueParseMode.STRICT); // Strict type parsing

    JsonDataSource jsonDataSource = new JsonDataSource("data.json", options);

    DocumentAssembler assembler = new DocumentAssembler();
    assembler.assembleDocument("Template.docx", "Output.docx",
        new DataSourceInfo(jsonDataSource, "data"));
}

In the default JsonSimpleValueParseMode.LOOSE mode, the types of JSON simple values are determined by parsing their string representations, so a string such as "42" becomes a number. In the STRICT mode, the types are determined by the JSON notation, so "42" remains a string.

Warning
By default, if a root JSON element is an object with only one property that is an object or array, the engine skips the root object. Call setAlwaysGenerateRootObject(true) to always include it.

Advanced Usage Topics

To learn more about working with complex JSON structures, date-time parsing, and advanced JsonDataSource options, please refer to the advanced usage section.

More resources

GitHub Examples

You may easily run the code above and see the feature in action in our GitHub examples:

Free Online Apps

Along with the full-featured Java library, we provide simple but powerful free online apps.

To assemble documents from templates and data sources, you can use the online apps from the GroupDocs.Assembly App Product Family.

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