How to read a file in AWS Lambda Function written in Java ?

Question

I have written an AWS Lambda Handler as below :

package com.lambda;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.r         


        

Answer 1

If the file is located under resources folder, you can use it directly in lambda by using something like the following code:

final BufferedReader br = new BufferedReader(new FileReader("/flows/cancellation/MessageArray.json"));

I wanted to read a json file, you can have different use case, but the code works.

Answer 2

If the file in located under resources directory, then the following solution should work:

String fileName = "resources/config.json";

Path path = Paths.get(this.getClass().getResource("/").toURI());
Path resourceLocation = path.resolve(fileName);

try(InputStream configStream = Files.newInputStream(resourceLocation)) {
            //use your file stream as you need.
}

Here the most important part is "resources/config.json", it must not be "/resources/config.json", because the file location is /var/task/resources/config.json in lambda, I checked.

Hope this helps who still face problem in reading file in aws lambda.

Answer 3

This is how I did it, let's say this is how your project structure looks like -

And you want to read the file config.properties which is inside the project-dir/resources directory.

The code for reading the content of the file would be -

InputStream input = null;
try {
    Path path = Paths.get(PropertyUtility.class.getResource("/").toURI());

    // The path for config file in Lambda Instance -
    String resourceLoc = path + "/resources/config.properties";

    input = new FileInputStream(resourceLoc);
} catch(Exception e) {
    // Do whatever
}

If you are following this project structure and using this code, then it will work in AWS Lambda.

PropertyUtility is just a utility class that I have created to read the contents of the config file. The PropertyUtility class looks like this -

As you can see in the above code, the path of the config file is different in the local system and in Lambda Instance.

In your local machine, PropertyUtility.class.getResource("/") points to bin, that is why you have to do path.getParent(), to point it to the project-directory which is HelloLambda in this example.

For the Lambda Instance, PropertyUtility.class.getResource("/") points directly to the project-directory.

Answer 4

I have made following changes in my code and now its works perfect :

Majorly changed following two lines :

ClassLoader classLoader = getClass().getClassLoader();

File cityFile = new File(classLoader.getResource("City.db").getFile());

package com.lambda;


import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.LambdaLogger;
import com.amazonaws.services.lambda.runtime.RequestStreamHandler;
import java.io.*;

public class TestDetailsHandler implements RequestStreamHandler {


    public void  handleRequest(InputStream input,OutputStream output,Context context){

        // Get Lambda Logger
        LambdaLogger logger = context.getLogger();

        // Receive the input from Inputstream throw exception if any

        ClassLoader classLoader = getClass().getClassLoader();

        File cityFile = new File(classLoader.getResource("City.db").getFile());
        FileInputStream fis = null;

        try {
            fis = new FileInputStream(cityFile);

            System.out.println("Total file size to read (in bytes) : "
                    + fis.available());

            int content;
            while ((content = fis.read()) != -1) {
                // convert to char and display it
                System.out.print((char) content);
            }

        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fis != null)
                    fis.close();
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
    }