Eclipse RCP 整合 IoC 容器實戰：基於 ASM 字節碼增強與 Java Agent 的無侵入依賴注入

動機：RCP 插件間解耦痛點

• Eclipse RCP 基於 **插件 + 擴展點** 機制，插件間物理依賴強 (需在 `MANIFEST.MF` `Require-Bundle`)。
• 單例服務 (數據源、日志、偏好設置) 獲取方式碎片化：`Platform.getService()`、`Activator.getDefault().getService()`、JNDI 等。
• 期望：**聲明式依賴注入** (`@Inject`/`@Autowired`)，容器自動裝配，業務代碼零容器 API 污染。

技術棧選型

核心註解定義

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Serviceable {} // 標記類需容器管理

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Injected {
    boolean optional() default false; // 依賴可選
}
// 用法示例
@Serviceable
public class ViewPartImpl extends ViewPart {
    private IFortuneCookie cookie;
    
    @Injected(optional = false)
    public void setCookie(IFortuneCookie cookie) { this.cookie = cookie; }
}

Java Agent 字節碼增強流程

public class IOCTransformer implements ClassFileTransformer {
    @Override
    public byte[] transform(ClassLoader loader, String className, Class redefined,
                            ProtectionDomain pd, byte[] bytecode) {
        // 1. 掃描類註解
        ClassReader cr = new ClassReader(bytecode);
        ClassAnnotationVisitor cav = new ClassAnnotationVisitor(new ConstructorVisitor());
        cr.accept(cav, ClassReader.SKIP_DEBUG);
        
        // 2. 若無 @Serviceable 或無構造器，直接返回
        if (cav.getConstructors().isEmpty()) return null;
        
        // 3. 增強所有構造器：插入 ServiceLocator.service(this)
        ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
        ClassConstructorWriter ccw = new ClassConstructorWriter(cav.getConstructors(), cw);
        cr.accept(ccw, 0);
        return cw.toByteArray();
    }
    
    // Agent 入口
    public static void premain(String args, Instrumentation inst) {
        inst.addTransformer(new IOCTransformer());
    }
}

ASM Visitor 關鍵邏輯

// 識別 @Serviceable 類註解
class ClassAnnotationVisitor extends ClassVisitor {
    private boolean serviceable = false;
    private ConstructorVisitor cv;
    
    @Override
    public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
        if (visible && desc.equals("Lcom/example/Serviceable;")) serviceable = true;
        return super.visitAnnotation(desc, visible);
    }
    @Override
    public MethodVisitor visitMethod(int access, String name, String desc, String sig, String[] ex) {
        return serviceable ? cv.visitMethod(access, name, desc, sig, ex) : null; // 非目標類直接忽略
    }
}

// 收集構造器
class ConstructorVisitor extends MethodVisitor {
    private List constructors = new ArrayList<>();
    @Override
    public void visitMethod(int access, String name, String desc, String sig, String[] ex) {
        if (name.equals("") && Type.getReturnType(desc).equals(Type.VOID_TYPE)) {
            constructors.add(new ConstructorInfo(access, desc));
        }
    }
}

// 增強構造器：插入靜態方法調用
class ClassConstructorWriter extends ClassVisitor {
    @Override
    public MethodVisitor visitMethod(int access, String name, String desc, String sig, String[] ex) {
        MethodVisitor mv = super.visitMethod(access, name, desc, sig, ex);
        if (isTargetConstructor(name, desc)) {
            return new MethodVisitor(Opcodes.ASM5, mv) {
                @Override
                public void visitCode() {
                    super.visitCode();
                    // 插入: ServiceLocator.service(this)
                    mv.visitVarInsn(Opcodes.ALOAD, 0); // this
                    mv.visitMethodInsn(Opcodes.INVOKESTATIC,
                        "com/example/ServiceLocator", "service",
                        "(Ljava/lang/Object;)V", false);
                }
            };
        }
        return mv;
    }
}

ServiceLocator 容器實現 (Eclipse 插件)

public class ServiceLocator {
    private static ServiceLocator INSTANCE = new ServiceLocator();
    private Map, IServiceFactory> factories = new ConcurrentHashMap<>();
    private Set