The S3 object key and bucket name are passed into your Lambda function via the event parameter. You can then get the object from S3 and read its contents.
Basic code to retrieve bucket and object key from the Lambda event
is as follows:
exports.handler = function(event, context, callback) {
const bkt = event.Records[0].s3.bucket.name;
const key = decodeURIComponent(event.Records[0].s3.object.key.replace(/+/g, ' '));
};
Once you have the bucket and key, you can call getObject to retrieve the object:
const AWS = require('aws-sdk');
const s3 = new AWS.S3();
exports.handler = function(event, context, callback) {
// Retrieve the bucket & key for the uploaded S3 object that
// caused this Lambda function to be triggered
const Bucket = event.Records[0].s3.bucket.name;
const Key = decodeURIComponent(event.Records[0].s3.object.key.replace(/+/g, ' '));
// Retrieve the object
s3.getObject({ Bucket, Key }, function(err, data) {
if (err) {
console.log(err, err.stack);
callback(err);
} else {
console.log("Raw text:
" + data.Body.toString('ascii'));
callback(null, null);
}
});
};
Here's an updated JavaScript example using ES6-style code and promises, minus error-handling:
const AWS = require('aws-sdk');
const s3 = new AWS.S3();
exports.handler = async (event, context) => {
const Bucket = event.Records[0].s3.bucket.name;
const Key = decodeURIComponent(event.Records[0].s3.object.key.replace(/+/g, ' '));
const data = await s3.getObject({ Bucket, Key }).promise();
console.log("Raw text:
" + data.Body.toString('ascii'));
};
A number of posters have asked for the equivalent in Java, so here's an example:
package example;
import java.net.URLDecoder;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import com.amazonaws.services.lambda.runtime.events.S3Event;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3Client;
import com.amazonaws.services.s3.event.S3EventNotification.S3EventNotificationRecord;
public class S3GetTextBody implements RequestHandler<S3Event, String> {
public String handleRequest(S3Event s3event, Context context) {
try {
S3EventNotificationRecord record = s3event.getRecords().get(0);
// Retrieve the bucket & key for the uploaded S3 object that
// caused this Lambda function to be triggered
String bkt = record.getS3().getBucket().getName();
String key = record.getS3().getObject().getKey().replace('+', ' ');
key = URLDecoder.decode(key, "UTF-8");
// Read the source file as text
AmazonS3 s3Client = new AmazonS3Client();
String body = s3Client.getObjectAsString(bkt, key);
System.out.println("Body: " + body);
return "ok";
} catch (Exception e) {
System.err.println("Exception: " + e);
return "error";
}
}
}
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