Spring Boot 4.2.0-RC1 默认 Ubuntu 26.04，bindings 会启动失败

Spring Boot 4.2.0-RC1 一跑 spring-boot:build-image，默认 builder 已经换成 paketobuildpacks/ubuntu-resolute-builder，镜像基线是 Ubuntu 26.04（Resolute Raccoon）。4.1.1 和 4.2.0-M2 还是 builder-noble-java-tiny（24.04）。同一次默认构建还会塞进 spring-cloud-bindings 2.0.4，容器一启动就因为找不到 org.springframework.boot.env.EnvironmentPostProcessor 挂掉；这个接口在 4.0 标了 forRemoval，4.2 里已经删掉。关掉 bindings 之后镜像能起来，curl 返回 hello-42-rc1。

环境是 Spring Boot 4.2.0-RC1、Spring Framework 7.1.0-RC1、JDK 21.0.12.1，BOM 从 Spring Milestone 拉。发行说明见 Spring Boot 4.2.0-RC1 Release Notes，标签 v4.2.0-RC1（2026-10-22T17:04:34Z）。站点上 Spring Boot 4.2.0-M2：LDAPS SSL Bundle 与 OTLP 语义约定 还停在 M2，这篇按 RC1 实际构建和启动写。

默认 builder 换成 ubuntu-resolute

gh-51249 把默认 builder 切到 resolute，里程碑就是 4.2.0-RC1。BuildRequest 里的常量对得上：

# 4.2.0-RC1
static final String DEFAULT_BUILDER_IMAGE_NAME = "paketobuildpacks/ubuntu-resolute-builder";
static final String DEFAULT_RUN_IMAGE_NAME = "paketobuildpacks/ubuntu-resolute-run-tiny";

# 4.1.1 / 4.2.0-M2
static final String DEFAULT_BUILDER_IMAGE_NAME = "paketobuildpacks/builder-noble-java-tiny";

不配 builder、直接 mvn spring-boot:build-image，日志里拉到的就是 resolute：

[INFO]  > Pulled builder image 'paketobuildpacks/ubuntu-resolute-builder@sha256:e0e63bcda06248417da1ecc96047671a97e3afda665755f238b5bf78730a5f75'
[INFO]  > Pulled run image 'paketobuildpacks/ubuntu-resolute-run-tiny@sha256:8c0c4ab9e41e11ea7ead2f359e469c9bf64ec2f3bb8ab92041061b345354ff16'
[INFO] Successfully built image 'docker.io/library/boot42-rc1-demo:local'
[INFO] BUILD SUCCESS

builder 镜像标签和 /etc/os-release：

stack=io.buildpacks.stacks.resolute version=26.04

PRETTY_NAME="Ubuntu 26.04.1 LTS"
NAME="Ubuntu"
VERSION_ID="26.04"
VERSION="26.04.1 LTS (Resolute Raccoon)"
VERSION_CODENAME=resolute

应用镜像标签带 io.buildpacks.stacks.resolute.tiny 和 org.springframework.boot.version=4.2.0-RC1。发行说明里写：不配 builder 时 run image 默认 ubuntu-resolute-run-tiny（无 shell）；自己指定 builder 才会跟到带 shell 的 ubuntu-resolute-run。要留在 24.04 就把 builder 设回 paketobuildpacks/builder-noble-java-tiny。

默认塞进的 spring-cloud-bindings 让容器起不来

第一次默认构建时 creator 下载了 bindings 2.0.4：

[INFO]     [creator]         $BP_SPRING_CLOUD_BINDINGS_DISABLED   false                      whether to contribute Spring Boot cloud bindings support
[INFO]     [creator]         Downloading from https://repo1.maven.org/maven2/org/springframework/cloud/spring-cloud-bindings/2.0.4/spring-cloud-bindings-2.0.4.jar
[INFO] Successfully built image 'docker.io/library/boot42-rc1-demo:with-bindings'

docker run 立刻失败：

Caused by: java.lang.IllegalArgumentException: Unable to instantiate factory class [org.springframework.cloud.bindings.boot.BindingFlattenedEnvironmentPostProcessor] for factory type [org.springframework.context.ApplicationListener]
Caused by: java.lang.NoClassDefFoundError: org/springframework/boot/env/EnvironmentPostProcessor
Caused by: java.lang.ClassNotFoundException: org.springframework.boot.env.EnvironmentPostProcessor

Boot 4.1.1 的 spring-boot jar 里还有 org.springframework.boot.env.EnvironmentPostProcessor，源码标着 @Deprecated(since = "4.0.0", forRemoval = true)，说明里写 for removal in 4.2.0，改用 org.springframework.boot.EnvironmentPostProcessor。4.2.0-RC1 的 jar 里这个旧接口已经没了，bindings 2.0.4 还在引用旧包名。这是对着两个版本的 class 列表和 4.1.1 源码对出来的，不是猜的。

在 spring-boot-maven-plugin 里加上：

<image>
  <env>
    <BP_SPRING_CLOUD_BINDINGS_DISABLED>true</BP_SPRING_CLOUD_BINDINGS_DISABLED>
  </env>
</image>

重建后 creator 显示 $BP_SPRING_CLOUD_BINDINGS_DISABLED true，不再下 bindings jar。容器起来后：

2026-10-22T17:26:40.006Z  INFO 1 --- [boot42-rc1-demo] [           main] o.s.boot.tomcat.TomcatWebServer          : Tomcat started on port 8080 (http) with context path '/'
2026-10-22T17:26:40.012Z  INFO 1 --- [boot42-rc1-demo] [           main] c.e.boot42.Boot42Rc1DemoApplication      : Started Boot42Rc1DemoApplication in 1.583 seconds (process running for 1.909)
curl=hello-42-rc1

properties-migrator 的 fail 开关

RC1 还给 spring-boot-properties-migrator 加了 spring.properties.migrator.fail，取值 never（默认）、on-error、on-warning。依赖进 runtime 即可。

改名键（warning）配 on-error 时进程仍退出 0；换成已删除的 spring.banner.image.width（error）再配 on-error，启动失败：

$ java -jar target/boot42-rc1-demo-0.0.1-SNAPSHOT.jar --spring.banner.image.width=76 --spring.properties.migrator.fail=on-error
The use of configuration keys that are no longer supported was found in the environment:

Property source 'commandLineArgs':
	Key: spring.banner.image.width
		Reason: Support for image banners has been removed.

java.lang.IllegalStateException: Found configuration keys that need to be migrated
exit=1

改名键配 on-warning 同样 exit=1：

$ java -jar target/boot42-rc1-demo-0.0.1-SNAPSHOT.jar --spring.resources.add-mappings=false --spring.properties.migrator.fail=on-warning
The use of configuration keys that have been renamed was found in the environment:

Property source 'commandLineArgs':
	Key: spring.resources.add-mappings
		Replacement: spring.web.resources.add-mappings

java.lang.IllegalStateException: Found configuration keys that need to be migrated
exit=1

默认不设 fail（等同 never）时两种键都只打日志，进程 exit=0。

版本边界

Ubuntu resolute 默认 builder、run image 兼容检查改看 distro 标签、spring.properties.migrator.fail，都是 4.2.0-RC1 Release Notes 明文新内容；4.1.x / 4.2.0-M2 的 BuildRequest 仍指向 noble。org.springframework.boot.env.EnvironmentPostProcessor 的删除落在 4.2，4.1.1 里还能加载到。bindings 启动失败是这次默认构建实测到的，发行说明没有单独写这一条。