How to Dynamically Capture Java Method Logs Without Restarting Your Cloud‑Native App

Real‑world systems are complex and traditional observability (trace, log, metric) often captures information at fixed points, making it hard to investigate unexpected issues. Log governance lets you configure rules in the console to collect data at any point without restarting the application.

Scenario: Debugging a Failed Database Call

Consider a simple request chain that calls a database. When an error occurs, you need the call stack, method parameters, return values, and exceptions to pinpoint the cause. Using log governance, you can create a rule that targets the /sql endpoint, enable exception filtering, and select stack trace collection.

After applying the rule, the system writes logs containing the full Java stack trace, for example:

at com.mysql.cj.jdbc.ClientPreparedStatement.executeQuery(ClientPreparedStatement.java:989)
at com.alibaba.druid.pool.DruidPooledPreparedStatement.executeQuery(DruidPooledPreparedStatement.java:213)
at com.alibabacloud.mse.demo.service.DruidCon.doCommond(DruidCon.java:57)
at com.alibabacloud.mse.demo.service.DruidService.query(DruidService.java:15)
at com.alibabacloud.mse.demo.BApplication$AController.sql(BApplication.java:89)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

The stack includes your own business methods (e.g., com.alibabacloud.mse.demo.service.DruidCon.doCommond and com.alibabacloud.mse.demo.service.DruidService.query), which you can further investigate.

Targeted Rule for a Specific Method

To capture parameters and other details for a particular method, add a new rule that specifies the method name (e.g., doCommond). Enable exception filtering and select request parameters in the output fields.

The resulting log entry is emitted in JSON format, such as:

{
  "appName": "app-b",
  "attributes": {
    "mse.tag": "base",
    "mse.param": "{\"sql\":\"select * from log_demo where id = ?\",\"id\":\"1\"}",
    "mse.app.tag": "base",
    "mse.service.type": "CUSTOM"
  },
  "endTime": 1665974434728,
  "ip": "10.0.0.166",
  "name": "com.alibabacloud.mse.demo.service.DruidCon:doCommond(java.lang.String,int)",
  "needRecord": true,
  "parentId": -4669550334584716586,
  "ruleIdSet": [288],
  "spanId": -8047278153886744300,
  "startTime": 1665974434725,
  "statusCode": 2,
  "traceId": "ea1a00009d16659744347231724d0001"
}

This demonstrates that log governance can collect arbitrary information at any Java method point without adding code or restarting the service, greatly simplifying troubleshooting of issues that are hard to reproduce in test environments.

Exporting Logs to a Log Service

After enabling log governance, logs are automatically rolled to a local file ( /home/admin/.opt/ArmsAgent/logs/mse-log-governance.log or, when using OneAgent,

/home/admin/.opt/ArmsAgent/plugins/ArmsAgent/logs/mse-log-governance.log

). To analyze them centrally, you can configure Alibaba Cloud SLS Logtail to collect the file.

Log path: /home/admin/.opt/ArmsAgent/logs/mse-log-governance.log Enable the Docker file switch if the logs are from a Docker container.

Enable the K8s deployment switch for Kubernetes environments.

Select JSON mode for parsing.

In the SLS console, you may let the system auto‑create indexes or manually add indexes for fields such as statusCode, ruleIdSet, name, and appName to facilitate queries.

Viewing and Analyzing Collected Logs

After a short delay, the logs appear in the SLS console where you can use the built‑in query and analysis tools to filter, search, and visualize the collected data.

Conclusion

Log governance provides zero‑code, dynamic data collection at any point in a Java application, reducing the need for redeployment and helping resolve hard‑to‑reproduce issues. Collected data is stored as JSON, compatible with OpenTelemetry standards, and can be forwarded to log services like SLS for further processing.