Question

我试图从XML文件中检索一些Java Bean的描述。我想在项目@Data中使用lombok对它们进行注释，以自动包含构造函数，equals，hashCode，getters，setter和toString。我想在内存中编译它们，生成一些实例（使用来自相同XML文件的数据）并将它们添加到Drools以最终对该数据做一些推理。

不幸的是，我无法编译这些课程，所以我在寻求你的帮助！

以下代码显示了如何以编程方式在内存中编译Java类：

package example;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.ToolProvider;

public class Simple {

    public static void main(String[] args) throws Exception {
        String name = "Person";
        String content = //
            "public class " + name + " {\n" + //
            "    @Override\n" + //
            "    public String toString() {\n" + //
            "        return \"Hello, world!\";\n" + //
            "    }\n" + //
            "}\n";
        System.out.println(content);

        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        JavaFileManager manager = new MemoryFileManager(compiler.getStandardFileManager(null, null, null));

        List<String> options = new ArrayList<String>();
        options.addAll(Arrays.asList("-classpath", System.getProperty("java.class.path")));

        List<JavaFileObject> files = new ArrayList<JavaFileObject>();
        files.add(new MemoryJavaFileObject(name, content));

        compiler.getTask(null, manager, null, options, null, files).call();

        Object instance = manager.getClassLoader(null).loadClass(name).newInstance();
        System.out.println(instance);
    }

}

其中MemoryFileManager是：

package example;

import java.io.IOException;
import java.security.SecureClassLoader;

import javax.tools.FileObject;
import javax.tools.ForwardingJavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.JavaFileObject.Kind;
import javax.tools.StandardJavaFileManager;

public class MemoryFileManager extends ForwardingJavaFileManager<StandardJavaFileManager> {

    private MemoryJavaClassObject object;

    public MemoryFileManager(StandardJavaFileManager manager) {
        super(manager);
    }

    @Override
    public ClassLoader getClassLoader(Location location) {
        return new SecureClassLoader() {
            @Override
            protected Class<?> findClass(String name) throws ClassNotFoundException {
                byte[] b = object.getBytes();
                return super.defineClass(name, object.getBytes(), 0, b.length);
            }
        };
    }

    @Override
    public JavaFileObject getJavaFileForOutput(Location location, String name, Kind kind, FileObject sibling) throws IOException {
        object = new MemoryJavaClassObject(name, kind);
        return object;
    }

}

和MemoryJavaClassObject是：

package example;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URI;

import javax.tools.SimpleJavaFileObject;

public class MemoryJavaClassObject extends SimpleJavaFileObject {

    protected final ByteArrayOutputStream stream = new ByteArrayOutputStream();

    public MemoryJavaClassObject(String name, Kind kind) {
        super(URI.create("string:///" + name.replace('.', '/') + kind.extension), kind);
    }

    public byte[] getBytes() {
        return stream.toByteArray();
    }

    @Override
    public OutputStream openOutputStream() throws IOException {
        return stream;
    }

}

最后MemoryJavaFileObject是：

package example;

import java.net.URI;

import javax.tools.SimpleJavaFileObject;

public class MemoryJavaFileObject extends SimpleJavaFileObject {

    private CharSequence content;

    protected MemoryJavaFileObject(String className, CharSequence content) {
        super(URI.create("string:///" + className.replace('.', '/') + Kind.SOURCE.extension), Kind.SOURCE);
        this.content = content;
    }

    @Override
    public CharSequence getCharContent(boolean ignoreEncodingErrors) {
        return content;
    }

}

如果我在第一个代码块中运行该示例，我会得到以下输出，如预期的那样：

public class Person {
    @Override
    public String toString() {
        return "Hello, world!";
    }
}

Hello, world!

现在，如果我将lombok.jar添加到我的项目中，并且包含以下示例：

package example;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileManager;
import javax.tools.JavaFileObject;
import javax.tools.ToolProvider;

public class Lombok {

    public static void main(String[] args) throws Exception {
        String name = "Person";
        String content = //
            "import lombok.Data;\n" + //
            "public @Data class " + name + " {\n" + //
            "    private String name;\n" + //
            "}\n";
        System.out.println(content);

        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        JavaFileManager manager = new MemoryFileManager(compiler.getStandardFileManager(null, null, null));

        List<String> options = new ArrayList<String>();
        options.addAll(Arrays.asList("-classpath", System.getProperty("java.class.path")));

        List<JavaFileObject> files = new ArrayList<JavaFileObject>();
        files.add(new MemoryJavaFileObject(name, content));

        compiler.getTask(null, manager, null, options, null, files).call();

        Object instance = manager.getClassLoader(null).loadClass(name).newInstance();
        System.out.println(instance);
    }

}

不幸的是，我没有得到预期的输出，而是：

import lombok.Data;
public @Data class Person {
    private String name;
}

/Person.java:2: warning: Can't initialize javac processor due to (most likely) a class loader     problem: java.lang.NoClassDefFoundError: com/sun/tools/javac/processing/JavacProcessingEnvironment
public @Data class Person {
             ^
      at lombok.javac.apt.Processor.init(Processor.java:84)
      at lombok.core.AnnotationProcessor$JavacDescriptor.want(AnnotationProcessor.java:87)
      at lombok.core.AnnotationProcessor.init(AnnotationProcessor.java:141)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment$ProcessorState.<init>(JavacProcessingEnvironment.java:500)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment$DiscoveredProcessors$ProcessorStateIterator.next(JavacProcessingEnvironment.java:597)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.discoverAndRunProcs(JavacProcessingEnvironment.java:690)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1800(JavacProcessingEnvironment.java:91)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.run(JavacProcessingEnvironment.java:1035)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1176)
      at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1173)
      at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:859)
      at com.sun.tools.javac.main.Main.compile(Main.java:523)
      at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
      at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
      at example.Lombok.main(Lombok.java:42)
  Caused by: java.lang.ClassNotFoundException: com.sun.tools.javac.processing.JavacProcessingEnvironment
      at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
      at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
      at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
      ... 15 more
1 warning
Person@39aeed2f

请注意，由于显示了典型输出，因此编译了类并执行了默认的toString()方法。另请注意，如果我运行前一个示例，现在我得到以下内容：

public class Person {
    @Override
    public String toString() {
        return "Hello, world!";
    }
}

/Person.java:1: warning: Can't initialize javac processor due to (most likely) a class loader problem: java.lang.NoClassDefFoundError: com/sun/tools/javac/processing/JavacProcessingEnvironment
public class Person {
       ^
      at lombok.javac.apt.Processor.init(Processor.java:84)
      at lombok.core.AnnotationProcessor$JavacDescriptor.want(AnnotationProcessor.java:87)
      at lombok.core.AnnotationProcessor.init(AnnotationProcessor.java:141)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment$ProcessorState.<init>(JavacProcessingEnvironment.java:500)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment$DiscoveredProcessors$ProcessorStateIterator.next(JavacProcessingEnvironment.java:597)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.discoverAndRunProcs(JavacProcessingEnvironment.java:690)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1800(JavacProcessingEnvironment.java:91)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.run(JavacProcessingEnvironment.java:1035)
      at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1176)
      at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1173)
      at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:859)
      at com.sun.tools.javac.main.Main.compile(Main.java:523)
      at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
      at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
      at example.Simple.main(Simple.java:44)
  Caused by: java.lang.ClassNotFoundException: com.sun.tools.javac.processing.JavacProcessingEnvironment
      at java.net.URLClassLoader$1.run(URLClassLoader.java:372)
      at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
      at java.security.AccessController.doPrivileged(Native Method)
      at java.net.URLClassLoader.findClass(URLClassLoader.java:360)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
      at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
      at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
      ... 15 more
1 warning
Hello, world!

显然，通过查看异常传递的警告消息，lombok没有正确挂钩给定的编译器。不幸的是，我无法找到任何有用的信息。我只能认为lombok无法正确使用Java JDK 8.我是对的吗？

你知道其他解决这个问题的方法吗？

Answer 1

感谢Holger，我成功地解决了这个问题。

问题是由于类路径中缺少tools.jar引起的。这是因为Eclipse默认将Java环境识别为JRE而不是JDK。

最重要的是，Java JDK可能 - 或者可能不是，具体取决于您拥有的版本 - 具有tools.jar文件。

如果你有Java 7或8，那么你应该在$JAVA_HOME/lib/tools.jar中拥有这样的库。

如果您使用的是Java 6，则该文件不存在，但$JAVA_HOME/Classes/classes.jar提供了相同的功能。

编译器是Java 6中添加的功能，因此如果您想使用它并且您拥有旧版本的Java，则应首先更新您的环境。

现在，有几种方法可以将tools.jar（或classes.jar）包含到项目的类路径中;因为我使用gradle，所以我决定将它作为依赖项引入，如下面的代码片段所示：

dependencies {
    compile files("${System.properties['java.home']}/../lib/tools.jar")
    compile 'org.projectlombok:lombok:1.14.4'
    testCompile 'junit:junit:4.11'
}

希望这个小小的解释可以帮助其他人面临类似的问题！

干杯！

使用`lombok`注释和Java JDK 8在内存中编译Java类

1 个答案: