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AWS SDK for Java
Developer Guide

Logging AWS SDK for Java Calls

The AWS SDK for Java is instrumented with Apache Commons Logging, which is an abstraction layer that enables the use of any one of several logging systems at runtime.

Supported logging systems include the Java Logging Framework and Apache Log4j, among others. This topic shows you how to use Log4j. You can use the SDK's logging functionality without making any changes to your application code.

To learn more about Log4j, see the Apache website.

Note

This topic focuses on Log4j 1.x. Log4j2 doesn't directly support Apache Commons Logging, but provides an adapter that directs logging calls automatically to Log4j2 using the Apache Commons Logging interface. For more information, see Commons Logging Bridge in the Log4j2 documentation.

Download the Log4J JAR

To use Log4j with the SDK, you need to download the Log4j JAR from the Apache website. The SDK doesn't include the JAR. Copy the JAR file to a location that is on your classpath.

Log4j uses a configuration file, log4j.properties. Example configuration files are shown below. Copy this configuration file to a directory on your classpath. The Log4j JAR and the log4j.properties file don't have to be in the same directory.

The log4j.properties configuration file specifies properties such as logging level, where logging output is sent (for example, to a file or to the console), and the format of the output. The logging level is the granularity of output that the logger generates. Log4j supports the concept of multiple logging hierarchies. The logging level is set independently for each hierarchy. The following two logging hierarchies are available in the AWS SDK for Java:

  • log4j.logger.com.amazonaws

  • log4j.logger.org.apache.http.wire

Setting the Classpath

Both the Log4j JAR and the log4j.properties file must be located on your classpath. If you're using Apache Ant, set the classpath in the path element in your Ant file. The following example shows a path element from the Ant file for the Amazon S3 example included with the SDK.

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<path id="aws.java.sdk.classpath"> <fileset dir="../../third-party" includes="**/*.jar"/> <fileset dir="../../lib" includes="**/*.jar"/> <pathelement location="."/> </path>

If you're using the Eclipse IDE, you can set the classpath by opening the menu and navigating to Project | Properties | Java Build Path.

Service-Specific Errors and Warnings

We recommend that you always leave the "com.amazonaws" logger hierarchy set to "WARN" to catch any important messages from the client libraries. For example, if the Amazon S3 client detects that your application hasn't properly closed an InputStream and could be leaking resources, the S3 client reports it through a warning message to the logs. This also ensures that messages are logged if the client has any problems handling requests or responses.

The following log4j.properties file sets the rootLogger to WARN, which causes warning and error messages from all loggers in the "com.amazonaws" hierarchy to be included. Alternatively, you can explicitly set the com.amazonaws logger to WARN.

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log4j.rootLogger=WARN, A1 log4j.appender.A1=org.apache.log4j.ConsoleAppender log4j.appender.A1.layout=org.apache.log4j.PatternLayout log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n # Or you can explicitly enable WARN and ERROR messages for the AWS Java clients log4j.logger.com.amazonaws=WARN

Request/Response Summary Logging

Every request to an AWS service generates a unique AWS request ID that is useful if you run into an issue with how an AWS service is handling a request. AWS request IDs are accessible programmatically through Exception objects in the SDK for any failed service call, and can also be reported through the DEBUG log level in the "com.amazonaws.request" logger.

The following log4j.properties file enables a summary of requests and responses, including AWS request IDs.

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log4j.rootLogger=WARN, A1 log4j.appender.A1=org.apache.log4j.ConsoleAppender log4j.appender.A1.layout=org.apache.log4j.PatternLayout log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n # Turn on DEBUG logging in com.amazonaws.request to log # a summary of requests/responses with AWS request IDs log4j.logger.com.amazonaws.request=DEBUG

Here is an example of the log output.

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2009-12-17 09:53:04,269 [main] DEBUG com.amazonaws.request - Sending Request: POST https://rds.amazonaws.com / Parameters: (MaxRecords: 20, Action: DescribeEngineDefaultParameters, SignatureMethod: HmacSHA256, AWSAccessKeyId: ACCESSKEYID, Version: 2009-10-16, SignatureVersion: 2, Engine: mysql5.1, Timestamp: 2009-12-17T17:53:04.267Z, Signature: q963XH63Lcovl5Rr71APlzlye99rmWwT9DfuQaNznkD, ) 2009-12-17 09:53:04,464 [main] DEBUG com.amazonaws.request - Received successful response: 200, AWS Request ID: 694d1242-cee0-c85e-f31f-5dab1ea18bc6 2009-12-17 09:53:04,469 [main] DEBUG com.amazonaws.request - Sending Request: POST https://rds.amazonaws.com / Parameters: (ResetAllParameters: true, Action: ResetDBParameterGroup, SignatureMethod: HmacSHA256, DBParameterGroupName: java-integ-test-param-group-0000000000000, AWSAccessKeyId: ACCESSKEYID, Version: 2009-10-16, SignatureVersion: 2, Timestamp: 2009-12-17T17:53:04.467Z, Signature: 9WcgfPwTobvLVcpyhbrdN7P7l3uH0oviYQ4yZ+TQjsQ=, ) 2009-12-17 09:53:04,646 [main] DEBUG com.amazonaws.request - Received successful response: 200, AWS Request ID: 694d1242-cee0-c85e-f31f-5dab1ea18bc6

Verbose Wire Logging

In some cases, it can be useful to see the exact requests and responses that the AWS SDK for Java sends and receives. You shouldn't enable this logging in production systems because writing out large requests (e.g., a file being uploaded to Amazon S3) or responses can significantly slow down an application. If you really need access to this information, you can temporarily enable it through the Apache HttpClient 4 logger. Enabling the DEBUG level on the apache.http.wire logger enables logging for all request and response data.

The following log4j.properties file turns on full wire logging in Apache HttpClient 4 and should only be turned on temporarily because it can have a significant performance impact on your application.

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log4j.rootLogger=WARN, A1 log4j.appender.A1=org.apache.log4j.ConsoleAppender log4j.appender.A1.layout=org.apache.log4j.PatternLayout log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %c - %m%n # Log all HTTP content (headers, parameters, content, etc) for # all requests and responses. Use caution with this since it can # be very expensive to log such verbose data! log4j.logger.org.apache.http.wire=DEBUG