我正在尝试将大型代码库从 Maven 迁移到 bazel，我发现一些测试写入target/classes and target/test-classes并且生产代码将其读取为类路径上的资源。这是因为 maven Surefire/failsafe 默认从模块目录运行并添加target/classes and target/test-classes到类路径。 对于我来说，要迁移这个大型代码库，唯一合理的解决方案是创建 target、target/classes 和 target/test-classes 文件夹，并将最后两个添加到测试的类路径中。
关于如何实现这一目标有什么想法吗？

Thanks

另一种方法。创建自定义 javaagent 和自定义类加载器，而不是生成测试套件。使用jvm_flags来设置和配置它。

javaagent 有一个 premain 方法。这听起来像是一个自然的地方，可以在常规 main 方法之前执行一些操作，即使它们与类检测、调试、覆盖范围收集或 javaagent 的任何其他常用用途没有任何关系。

自定义javaagent读取系统属性extra.dirs并创建那里指定的目录。然后它读取属性extra.link.path并创建那里指定的符号链接，这样我就可以将资源放置在测试期望的位置，而不必复制它们。

需要类加载器，以便我们可以在运行时修改类路径而无需黑客攻击。最大的优点是该解决方案适用于 Java 10。

自定义类加载器读取系统属性extra.class.path并且（实际上）将其放在前面java.class.path.

以这种方式做事意味着可以使用标准 bazel 规则。

BUILD

runtime_classgen_dirs = ":".join([
            "target/classes",
            "target/test-classes",
])
java_test(
    ...,
    jvm_flags = [
        # agent
        "-javaagent:$(location //tools:test-agent_deploy.jar)",
        "-Dextra.dirs=" + runtime_classgen_dirs,
        # classloader
        "-Djava.system.class.loader=ResourceJavaAgent",
        "-Dextra.class.path=" + runtime_classgen_dirs,
    ],
    ,,,,
    deps = [
        # not runtime_deps, cause https://github.com/bazelbuild/bazel/issues/1566
        "//tools:test-agent_deploy.jartest-agent_deploy.jar"
    ],
    ...,
)

工具/构建

java_binary(
    name = "test-agent",
    testonly = True,
    srcs = ["ResourceJavaAgent.java"],
    deploy_manifest_lines = ["Premain-Class: ResourceJavaAgent"],
    main_class = "ResourceJavaAgent",
    visibility = ["//visibility:public"],
)

工具/资源 JavaAgent.java

import java.io.File;
import java.io.IOException;
import java.lang.instrument.Instrumentation;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;

// https://stackoverflow.com/questions/60764/how-should-i-load-jars-dynamically-at-runtime
public class ResourceJavaAgent extends URLClassLoader {
    private final ClassLoader parent;

    public ResourceJavaAgent(ClassLoader parent) throws MalformedURLException {
        super(buildClassPath(), null);
        this.parent = parent; // I need the parent as backup for SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
        System.out.println("initializing url classloader");
    }

    private static URL[] buildClassPath() throws MalformedURLException {
        final String JAVA_CLASS_PATH = "java.class.path";
        final String EXTRA_CLASS_PATH = "extra.class.path";
        List<String> paths = new LinkedList<>();
        paths.addAll(Arrays.asList(System.getProperty(EXTRA_CLASS_PATH, "").split(File.pathSeparator)));
        paths.addAll(Arrays.asList(System.getProperty(JAVA_CLASS_PATH, "").split(File.pathSeparator)));
        URL[] urls = new URL[paths.size()];
        for (int i = 0; i < paths.size(); i++) {
            urls[i] = Paths.get(paths.get(i)).toUri().toURL(); // important only for resource url, really: this url must be absolute, to pass getClass().getResource("/users.properties").toURI()) with uri that isOpaque == false.
//            System.out.println(urls[i]);
        }
        // this is for spawnVM functionality in tests
        System.setProperty(JAVA_CLASS_PATH, System.getProperty(EXTRA_CLASS_PATH, "") + File.pathSeparator + System.getProperty(JAVA_CLASS_PATH));
        return urls;
    }

    @Override
    public Class<?> loadClass(String s) throws ClassNotFoundException {
        try {
            return super.loadClass(s);
        } catch (ClassNotFoundException e) {
            return parent.loadClass(s);  // we search parent second, not first, as the default URLClassLoader would
        }
    }

    private static void createRequestedDirs() {
        for (String path : System.getProperty("extra.dirs", "").split(File.pathSeparator)) {
            new File(path).mkdirs();
        }
    }

    private static void createRequestedLinks() {
        String linkPaths = System.getProperty("extra.link.path", null);
        if (linkPaths == null) {
            return;
        }
        for (String linkPath : linkPaths.split(",")) {
            String[] fromTo = linkPath.split(":");
            Path from = Paths.get(fromTo[0]);
            Path to = Paths.get(fromTo[1]);
            try {
                Files.createSymbolicLink(from.toAbsolutePath(), to.toAbsolutePath());
            } catch (IOException e) {
                throw new IllegalArgumentException("Unable to create link " + linkPath, e);
            }
        }
    }

    public static void premain(String args, Instrumentation instrumentation) throws Exception {
        createRequestedDirs();
        createRequestedLinks();
    }
}