How can I use apache camel bindy to convert java pojo to fixed length string that has a list attribute?

Question

I have a java pojo class as the following?

@FixedLengthRecord
public class Request {
    @DataField(pos = 1, length = 15)
    private String string1;

    @DataField(pos = 16, length = 8)
    private String string2;

    @DataField(pos = 24)
    @ManytoOne(mappedTo="classpath:Record")
    private List<Record> records;
}

public class Record{
   
    @DataField(pos = 24, length = 10)
    private String string3;

    @DataField(pos = 34, length = 10)
    private String string4;

    @DataField(pos = 44, length = 8)
    private String string5;
}

I want to convert the pojo class to fixedLength string using apache camel? But the List attributes never gets converted to fixed length string. Is there a way to do this using just one route?

I tried the following:

public class CamelBindyUtility extends RouteBuilder {

    @Override
    public void configure() throws Exception {
 
        from("direct:marshal")
            .marshal().bindy(BindyFixedLengthDataFormat.class, Request.class)
            .to("mock:marshalled");
    }
}

It does not change the List attribute to the necessary fixed length?

Answer 1

To convert a POJO class to a fixed-length string using Apache Camel, especially when dealing with List properties, special measures need to be taken since Apache Camel's Bindy component doesn't natively support serializing or deserializing list properties within a POJO directly into a fixed-length format. However, you can achieve this requirement by combining Camel's capabilities with some programming techniques.

Example:

Create a Custom Processor: First, you need to create a custom processor (Processor) in which you will write logic to manually convert the Request object and its contained List into a fixed-length string format.

Processor Logic: In the custom processor, you need to iterate over the List<Record> in the Request and generate a fixed-length string for each Record. These strings will then be combined with the other fields of the Request object to form the final fixed-length string.

Implementing the Custom Processor

You can improve on this later by using reflection to achieve more flexible processing.

import org.apache.camel.Exchange;
import org.apache.camel.Processor;

public class FixedLengthProcessor implements Processor {
    @Override
    public void process(Exchange exchange) throws Exception {
        Request request = exchange.getIn().getBody(Request.class);
        StringBuilder fixedLengthString = new StringBuilder();

        // Process the basic properties of Request
        fixedLengthString.append(formatString(request.getString1(), 15));
        fixedLengthString.append(formatString(request.getString2(), 8));

        // Iterate over List<Record> and process each Record
        for (Record record : request.getRecords()) {
            fixedLengthString.append(formatString(record.getString3(), 10));
            fixedLengthString.append(formatString(record.getString4(), 10));
            fixedLengthString.append(formatString(record.getString5(), 8));
        }

        // Set the processed fixed-length string as the message body
        exchange.getIn().setBody(fixedLengthString.toString());
    }

    private String formatString(String input, int length) {
        if (input == null) input = "";
        if (input.length() > length) {
            return input.substring(0, length);
        } else {
            return String.format("%1$-" + length + "s", input);
        }
    }
}

Configuring the Camel Route: you can create a route that receives messages from an endpoint, processes them through the custom processor, and then sends the result to another endpoint.

from("direct:start")
    .process(new FixedLengthProcessor())
    .to("file://output?fileName=fixedLengthOutput.txt")