Convert PDF to Image (JPG, PNG) with ComPDFKit API and Java

Tutorials | ComPDFKit API · PDF to Image · Java Fri. 12 Apr. 2024

With ComPDFKit API library for Java, you not only have the capability to convert PDFs to images but also to and from other formats such as Word, Excel, PPT, images, HTML, JSON, and more. Try to use our 30 + PDF API tools online for free. Beyond just PDF conversion, our API libraries empower you to:

• Merge, split, insert, extract, and delete specific PDF pages

• OCR, watermark, or compress PDFs

• Compare documents (including content comparison and overlay comparison)

• Extract the images from the selected pages from PDFs

• Analyze and recognize text, images, paragraphs, headings, tables, etc. from PDFs

• Extract unstructured data from PDFs and save as structured data

To add converting PDF to images feature in Java projects in a few minutes, you can get started with the following steps.

Creating a Free API Account on ComPDFKit

In the first place, you could create a free ComPDFKit API account to get the credential of our API Java library. This free trial allows you to process 1000 documents per month, and you'll be able to access all our PDF API tools. After successfully log in your account, you'll enter the page below, providing an overview of your plan details.

Alt text: compdfkit api account dashboard

Setup Java Environment

1. Install Java 8 or above if you haven't already.

2. Run javac -version to verify your install.

3. Verify the JDK bin folder is included in the PATH variable (method varies by OS).

4. Install Maven using your preferred tool if you haven't already.

5. For this tutorial, you'll use IntelliJ IDEA as your primary code editor. To get started, create a new project called pdf_to_jpg. You can choose any location, but make sure to select Java as the language, Maven as the build system.

- Creating a Sample Project

- Install two libraries:

- OkHttp — This library makes API requests.

- JSON — This library will parse the JSON payload.

Open the pom.xml file and add the following dependencies to your project:

<dependencies>
    <dependency>
        <groupId>com.squareup.okhttp3</groupId>
        <artifactId>okhttp</artifactId>
        <version>4.9.2</version>
    </dependency>
</dependencies>

6. Open the main.java file and paste the code as in step2:

Use Java API Library to Convert PDF to Images

Step 1. Obtaining the API Key for Authentication

After you've verified your email, you can get your API key from the dashboard. In the menu on the left, click API Keys. You'll see the following page, which is an overview of your keys:

Get API Key for authentication

Now You need to replace public_key and secret_key with accessToken in the publicKey and secretKey authentication return values you get from the console.

import java.io.*;
import okhttp3.*;
public class main {
  public static void main(String []args) throws IOException{
    OkHttpClient client = new OkHttpClient().newBuilder()
      .build();
    MediaType mediaType = MediaType.parse("text/plain");
    // Building request parameters
    RequestBody body = RequestBody.create(mediaType, "{\n    \"publicKey\": \"{{public_key}}\",\n    \"secretKey\": \"{{secret_key}}\"\n}");
    Request request = new Request.Builder()
      .url("https://api-server.compdf.com/server/v1/oauth/token")
      .method("POST", body)
      .build();
    // Request results
    Response response = client.newCall(request).execute();
  }
}

Step 2: Run the Project to Convert PDF to Images

1. Creating Task for JPG and PNG

You need to replace the accessToken which was obtained from the previous step, and replace the language type you want to display the error information. After replacing them, you will get the taskId in the response data.

- PDF to JPG

import java.io.*;
import okhttp3.*;
public class main {
  public static void main(String []args) throws IOException{
    OkHttpClient client = new OkHttpClient().newBuilder()
      .build();
    MediaType mediaType = MediaType.parse("text/plain");
    // Building request parameters
    RequestBody body = RequestBody.create(mediaType, "");
    Request request = new Request.Builder()
      //pdf to jpg
      .url("https://api-server.compdf.com/server/v1/task/pdf/jpg?language={{language}}")
      .method("GET", body)
      .addHeader("Authorization", "Bearer {{accessToken}}")
      .build();
    // Request results
    Response response = client.newCall(request).execute();
  }
}

- PDF to PNG

import java.io.*;
import okhttp3.*;
public class main {
  public static void main(String []args) throws IOException{
    OkHttpClient client = new OkHttpClient().newBuilder()
      .build();
    MediaType mediaType = MediaType.parse("text/plain");
    // Building request parameters
    RequestBody body = RequestBody.create(mediaType, "");
    Request request = new Request.Builder()
      //pdf to png
      .url("https://api-server.compdf.com/server/v1/task/pdf/png?language={{language}}")
      .method("GET", body)
      .addHeader("Authorization", "Bearer {{accessToken}}")
      .build();
    // Request results
    Response response = client.newCall(request).execute();
  }
}

2. Uploading Files

Replace the file you want to convert, the taskId obtained in the previous step, the language type you want to display the error information, and the accessToken obtained in the first step.

Parameters:

pages：Value range: 1 to the maximum number of pages in the document (default: all pages).

imgDpi：Value range 72-1500 (default 300 , JPG support only).

import java.io.*;
import okhttp3.*;
public class main {
 public static void main(String []args) throws IOException{
   OkHttpClient client = new OkHttpClient().newBuilder()
    .build();
   MediaType mediaType = MediaType.parse("text/plain");
   // Building request parameters
   RequestBody body = new MultipartBody.Builder().setType(MultipartBody.FORM)
    .addFormDataPart("file","{{file}}",
   RequestBody.create(MediaType.parse("application/octet-stream"),
                                         new File("")))
    .addFormDataPart("taskId","{{taskId}}")
    .addFormDataPart("language","{{language}}")
   // PNG Param
   //.addFormDataPart("parameter","{ \"pages\":[1]}")
   // JPG Param
   //.addFormDataPart("parameter","{ \"imgDpi\": \"300\",\"pages\":[1]}")
    .addFormDataPart("password","")
    .build();
   Request request = new Request.Builder()
    .url("https://api-server.compdf.com/server/v1/file/upload")
    .method("POST", body)
    .addHeader("Authorization", "Bearer {{accessToken}}")
    .build();
   // Request results
   Response response = client.newCall(request).execute();
}
}

3. Processing Files

Replace the taskId you obtained from the Create task, and the accessToken obtained in the first step, and replace the language type you want to display the error information.

import java.io.*;
import okhttp3.*;
public class main {
public static void main(String []args) throws IOException{
  OkHttpClient client = new OkHttpClient().newBuilder()
    .build();
  MediaType mediaType = MediaType.parse("text/plain");
  RequestBody body = RequestBody.create(mediaType, "");
  // Building request parameters
  Request request = new Request.Builder()
    .url("https://api-server.compdf.com/server/v1/execute/start?taskId={{taskId}}&language={{language}}")
    .method("GET", body)
    .addHeader("Authorization", "Bearer {{accessToken}}")
    .build();
  // Request results
  Response response = client.newCall(request).execute();
}
}

4. Getting Task Information

Replace taskId with the taskId you obtained from the step "Create the task", access_token replaced by access_token obtained in the first step.

import java.io.*;
import okhttp3.*;
public class main {
 public static void main(String []args) throws IOException{
   OkHttpClient client = new OkHttpClient().newBuilder()
    .build();
   MediaType mediaType = MediaType.parse("text/plain");
   RequestBody body = RequestBody.create(mediaType, "");
   // Building request parameters
   Request request = new Request.Builder()
    .url("https://api-server.compdf.com/server/v1/task/taskInfo?taskId={{taskId}}")
    .method("GET", body)
    .addHeader("Authorization", "Bearer {{accessToken}}")
    .build();
   // Request results
   Response response = client.newCall(request).execute();
}
}

Final Words

You can now seamlessly integrate the PDF-to-image conversion capability into your current applications or systems through our PDF to Image API for Java. If you're interested in delving deeper into utilizing ComPDFKit's API library, our comprehensive documentation offers detailed tutorials on various functionalities such as converting images to PDFs, editing PDF pages, and more. Sign up a free ComPDFKit API account and explore our documentation for comprehensive insights into maximizing the potential of our API library.