python 的安装很耗时，在阿里云镜像中构建会超时。Java 的构建就比较快。所以我们可以从 Python 镜像来添加 Java 环境。

openjdk:8-jdk-alpine 的 Dockerfile（链接） 内容如下：

#
# NOTE: THIS DOCKERFILE IS GENERATED VIA "update.sh"
#
# PLEASE DO NOT EDIT IT DIRECTLY.
#

FROM alpine:3.8

# A few reasons for installing distribution-provided OpenJDK:
#
#  1. Oracle.  Licensing prevents us from redistributing the official JDK.
#
#  2. Compiling OpenJDK also requires the JDK to be installed, and it gets
#     really hairy.
#
#     For some sample build times, see Debian's buildd logs:
#       https://buildd.debian.org/status/logs.php?pkg=openjdk-8

# Default to UTF-8 file.encoding
ENV LANG C.UTF-8

# add a simple script that can auto-detect the appropriate JAVA_HOME value
# based on whether the JDK or only the JRE is installed
RUN { \
		echo '#!/bin/sh'; \
		echo 'set -e'; \
		echo; \
		echo 'dirname "$(dirname "$(readlink -f "$(which javac || which java)")")"'; \
	} > /usr/local/bin/docker-java-home \
	&& chmod +x /usr/local/bin/docker-java-home
ENV JAVA_HOME /usr/lib/jvm/java-1.8-openjdk
ENV PATH $PATH:/usr/lib/jvm/java-1.8-openjdk/jre/bin:/usr/lib/jvm/java-1.8-openjdk/bin

ENV JAVA_VERSION 8u191
ENV JAVA_ALPINE_VERSION 8.191.12-r0

RUN set -x \
	&& apk add --no-cache \
		openjdk8="$JAVA_ALPINE_VERSION" \
	&& [ "$JAVA_HOME" = "$(docker-java-home)" ]

# If you're reading this and have any feedback on how this image could be
# improved, please open an issue or a pull request so we can discuss it!
#
#   https://github.com/docker-library/openjdk/issues

把“FROM alpine:3.8”这一行替换为“FROM python:2.7.15-alpine”：

#
# NOTE: THIS DOCKERFILE IS GENERATED VIA "update.sh"
#
# PLEASE DO NOT EDIT IT DIRECTLY.
#

FROM python:2.7.15-alpine

# A few reasons for installing distribution-provided OpenJDK:
#
# 1. Oracle. Licensing prevents us from redistributing the official JDK.
#
# 2. Compiling OpenJDK also requires the JDK to be installed, and it gets
# really hairy.
#
# For some sample build times, see Debian's buildd logs:
# https://buildd.debian.org/status/logs.php?pkg=openjdk-8
# Default to UTF-8 file.encoding
ENV LANG C.UTF-8
# add a simple script that can auto-detect the appropriate JAVA_HOME value
# based on whether the JDK or only the JRE is installed
RUN { \
        echo '#!/bin/sh'; \
        echo 'set -e'; \
        echo; \
        echo 'dirname "$(dirname "$(readlink -f "$(which javac || which java)")")"'; \
    } > /usr/local/bin/docker-java-home \
    && chmod +x /usr/local/bin/docker-java-home
ENV JAVA_HOME /usr/lib/jvm/java-1.8-openjdk
ENV PATH $PATH:/usr/lib/jvm/java-1.8-openjdk/jre/bin:/usr/lib/jvm/java-1.8-openjdk/bin
ENV JAVA_VERSION 8u191
ENV JAVA_ALPINE_VERSION 8.191.12-r0
RUN set -x \
    && apk add --no-cache \
        openjdk8="$JAVA_ALPINE_VERSION" \
    && [ "$JAVA_HOME" = "$(docker-java-home)" ]
# If you're reading this and have any feedback on how this image could be
# improved, please open an issue or a pull request so we can discuss it!
#
# https://github.com/docker-library/openjdk/issues

然后构建，很快就能生成 Java 8 + Python 2.7 的 Docker 镜像。