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copybara-service merged 2 commits into from
Aug 28, 2024
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add markdown file to help with debugging #263

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add markdown file to help with debugging
lachlan-roberts Aug 27, 2024
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Merge remote-tracking branch 'origin/main' into debuggingGuide
lachlan-roberts Aug 28, 2024
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35 changes: 35 additions & 0 deletions debugging.md
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Expand Up @@ -13,3 +13,38 @@
See the License for the specific language governing permissions and
limitations under the License.
-->

# Google App Engine Java Debugging Guide

## Jetty Debug Logging

To enable debug logging in your web application, add a JUL `logging.properties` file under your application's `WEB-INF` directory.

In your `appengine-web.xml` file, specify the location of the logging file as a system property:

```xml
<system-properties>
<property name="java.util.logging.config.file" value="WEB-INF/logging.properties"/>
</system-properties>
```

For runtimes using the Jetty 9.4 code path (Java 8 - Java 17), there is a known issue where debug logging will not be output unless full debug logging is enabled with `.level=ALL`.

In the Java 21 runtime with Jetty 12, more granular debug logging is available. For example:
```
.level=INFO
org.eclipse.jetty.session.level=ALL
org.eclipse.jetty.server.level=ALL
```

## Jetty Server Dump

A Jetty Server Dump is useful for debugging issues by providing details about Jetty components and their configuration, including thread pools, connectors, contexts, classloaders, servlets, and more.

To enable a Jetty Server Dump after the `AppEngineWebAppContext` is started (which may occur after the first request in RPC mode), use the following system property:

```xml
<system-properties>
<property name="jetty.server.dumpAfterStart" value="true"/>
</system-properties>
```