# Monitor Java applications

Choose Actuator, Micrometer, JMX Exporter or built-in application metrics, then scrape them with Categraf or Prometheus.

Last reviewed 2026-10-11

By the end of this page, you will choose a suitable Java metrics endpoint and connect JVM or application metrics to Nightingale. Nightingale v9 does not scrape Java processes itself. Use **Categraf v0.5.17**, Prometheus or vmagent.

## Actuator[​](#actuator "Direct link to Actuator")

For a Spring Boot application, prefer Actuator. This example uses dependency management from **Spring Boot 3.5.x**:

```
<dependency>

  <groupId>org.springframework.boot</groupId>

  <artifactId>spring-boot-starter-actuator</artifactId>

</dependency>

<dependency>

  <groupId>io.micrometer</groupId>

  <artifactId>micrometer-registry-prometheus</artifactId>

</dependency>
```

Let the application's Spring Boot BOM manage versions instead of mixing Micrometer release lines. Expose the endpoint in `application.properties`:

```
management.server.port=8081

management.endpoints.web.exposure.include=health,prometheus
```

Allow the collector to access the management port. Adjust paths and credentials for Spring Security, proxies and custom application contexts.

```
curl --fail http://127.0.0.1:8081/actuator/prometheus
```

**Expected result**: Prometheus text with JVM metrics, not a login page, JSON error or 404. See the [Spring Boot 3.5 metrics documentation](https://docs.spring.io/spring-boot/3.5/reference/actuator/metrics.html).

## Micrometer[​](#micrometer "Direct link to Micrometer")

Without Spring Boot, use `micrometer-registry-prometheus`, register application meters with a shared `PrometheusMeterRegistry`, and serve its `scrape()` output over HTTP.

Package names vary between Micrometer and Prometheus client versions. Follow the [official example](https://docs.micrometer.io/micrometer/reference/implementations/prometheus.html) for your dependencies instead of copying old imports.

A registry without an HTTP endpoint cannot be scraped. Adding a registry dependency without binding JVM meters does not create all JVM metrics automatically.

## JMX[​](#jmx "Direct link to JMX")

For an application you cannot modify but that exposes MBeans, use the JMX Exporter Java Agent. This HTTP-mode example uses **JMX Exporter 1.3.0**. Put the jar and `jmx.yaml` in the working directory:

```
rules:

  - pattern: ".*"
```

```
java -javaagent:./jmx_prometheus_javaagent-1.3.0.jar=9404:./jmx.yaml -jar ./app.jar

curl --fail http://127.0.0.1:9404/metrics
```

**Expected result**: port 9404 returns Prometheus metrics. The broad rule is for initial verification; narrow it to required MBeans and restrict endpoint access for production. Use the [1.3.0 documentation](https://prometheus.github.io/jmx_exporter/1.3.0/java-agent/http-mode/) for the package and options.

## Built-in component metrics[​](#component-metrics "Direct link to Built-in component metrics")

Reuse a component's existing Prometheus endpoint rather than adding a second JMX collection path. Some middleware and service frameworks already expose `/metrics`; verify the format and authentication first. Metric names and labels vary, so choose matching dashboards and rules.

## Connect and verify[​](#verify "Direct link to Connect and verify")

Add the actual endpoint to `conf/input.prometheus/prometheus.toml`. This example matches the Actuator configuration above:

```
[[instances]]

urls = ["http://127.0.0.1:8081/actuator/prometheus"]

url_label_key = "instance"

url_label_value = "{{.Host}}"
```

```
./categraf --test --inputs prometheus
```

**Expected result**: metrics such as `jvm_` without scraping or parsing errors. Restart collection and check that new samples arrive in Nightingale's destination store. If Prometheus or vmagent already scrapes the application, register its store as a datasource without adding another scrape path.

## Next[​](#next "Direct link to Next")

* [Prometheus datasource](https://n9e.github.io/docs/data/prometheus.md)
* [Process monitoring](https://n9e.github.io/docs/practice/proc.md)