java - 错误的服务配置文件，或构造 Processor 对象时抛出的异常

Question

我正在用 Java 编写一个简单的自定义注释，但遇到了问题。这是我的代码的主要部分。

LogMeCustomAnnotation.java

package fun.n.learn.annotation;

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

// We need this annotation only till before compilation.
@Retention(RetentionPolicy.SOURCE)
// This is a simple custom annotation.
public @interface LogMeCustomAnnotation {

}

LogMeCustomAnnotationProcessor.java

package fun.n.learn.annotation;

import java.util.Set;

import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.Messager;
import javax.annotation.processing.RoundEnvironment;
import javax.annotation.processing.SupportedAnnotationTypes;
import javax.lang.model.element.TypeElement;
import javax.tools.Diagnostic;

// List the custom annotations that are supported.
@SupportedAnnotationTypes({ "fun.n.learn.annotation.LogMeCustomAnnotation" })
// Extend AbstractProcessor. This will let you process.
public class LogMeCustomAnnotationProcessor extends AbstractProcessor {

    @Override
    public boolean process(Set<? extends TypeElement> annotations,
            RoundEnvironment roundEnv) {

        Messager messager = processingEnv.getMessager();
        messager.printMessage(Diagnostic.Kind.NOTE, "I was here.");

        // TODO: Put some meaningful code here. Right now just get it to work.

        // return false;
        // We have already handled these annotations. No more. So return true.
        return true;
    }

}

/src/main/resources/META-INF/services/javax.annotation.processing.Processor

fun.n.learn.annotation.LogMeCustomAnnotationProcessor

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>fun.n.learn</groupId>
    <artifactId>javaCustomAnnotation</artifactId>
    <version>0.1.0</version>

    <build>
        <plugins>
            <plugin>
                <!-- Configure the project to use java 8 version. -->
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.5.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <!-- Disable annotation processing for ourselves. -->
                    <!-- <compilerArgument>-proc:none</compilerArgument> -->
                </configuration>
            </plugin>
        </plugins>
    </build>


</project>

现在，当我运行 mvn -e clean install 时，出现以下问题

[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] Bad service configuration file, or exception thrown while constructing Processor object: javax.annotation.processing.Processor: Provider fun.n.learn.annotation.LogMeCustomAnnotationProcessor not found
[INFO] 1 error

我一定是错过了一个简单的技巧。有什么帮助吗？

Answer 1

默认的 maven 生命周期运行 javac，javax.annotation.processing.Processor 文件作为类路径的一部分。这导致编译器期望文件中列出的注释处理器的编译实例。但是 LogMeCustomAnnotationProcessor 在那一刻没有编译，所以编译器会引发“Bad service configuration file ...”错误。参见 bug report .

为了解决这个问题，可以将maven编译阶段分开，先编译注解处理器，再编译整个项目。

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.5.1</version>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
            <executions>
                <execution>
                    <id>default-compile</id>
                    <configuration>
                        <compilerArgument>-proc:none</compilerArgument>
                        <includes>
                            <include>fun/n/learn/annotation/LogMeCustomAnnotationProcessor.java</include>
                            <!--include dependencies required for LogMeCustomAnnotationProcessor -->
                        </includes>
                    </configuration>
                </execution>
                <execution>
                    <id>compile-project</id>
                    <phase>compile</phase>
                    <goals>
                        <goal>compile</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

default-compile 执行编译 LogMeCustomAnnotationProcessor 并禁用注释处理，以便成功编译。
compile-project 编译整个项目并进行注解处理。