Mockito原理剖析—PowerMockito Mock静态方法原理、如何抑制静态初始化

文章目录

• • PowerMockito如何进行静态类的Mock
  • 如何抑制静态初始化

PowerMockito如何进行静态类的Mock

核心相关类

org.powermock.core.classloader.javassist.JavassistMockClassLoader

org.powermock.core.transformers.javassist.InstrumentMockTransformer

流程

PowerMockito通过自定义ClassLoader，在加载类之前，修改字节码中方法调用方的调用入口—将方法调用委托至MockGateway，从而实现方法拦截。

MockGateway

几种状态说明

状态	说明
PROCEED	进行实际的调用
SUPPRESS	对于Field，返回默认值 对于Method，抑制方法调用

几种方法说明

方法	说明
newInstanceCall	用于替换new {Class}(...)类型调用
fieldCall	用于替换dot access的属性访问
staticConstructorCall	用于替换静态初始化函数调用
constructorCall	用于替换构造函数调用
methodCall	用于替换普通方法调用

代码修改示例：

修改前

package powermock;

/**
 * @author lidelin.
 */
public class StaticMethodProvider {

    static {
        System.out.println("static init");
    }

    public static void provide() {
        System.out.println("ok");
    }

}

修改后

package powermock;

import java.io.PrintStream;
import javassist.runtime.Desc;
import org.powermock.core.MockGateway;
import org.powermock.core.classloader.PowerMockModified;

public class StaticMethodProvider implements PowerMockModified {
    public StaticMethodProvider() {
    }

    public static void provide() {
        Object var0 = MockGateway.methodCall(Desc.getClazz("powermock.StaticMethodProvider"), "provide", new Object[0], Desc.getParams("()"), "");
        if (var0 == MockGateway.PROCEED) {
            var0 = null;
            PrintStream var1 = null;
            Object var2 = MockGateway.fieldCall(var0, Desc.getClazz("java.lang.System"), "out", Desc.getType("Ljava/io/PrintStream;"));
            if (var2 == MockGateway.PROCEED) {
                var1 = System.out;
            } else {
                var1 = (PrintStream)var2;
            }

            PrintStream var10000 = var1;
            String var6 = "ok";
            PrintStream var5 = var10000;
            Object var3 = null;
            if (var5 != null) {
                var3 = var5;
            } else {
                var3 = Desc.getClazz("java.io.PrintStream");
            }

            Object var4 = MockGateway.methodCall(var3, "println", new Object[]{var6}, Desc.getParams("(Ljava/lang/String;)V"), "");
            if (var4 == MockGateway.PROCEED) {
                var5.println(var6);
                var2 = null;
            }

        }
    }

    static {
        PrintStream var0 = null;
        PrintStream var1 = null;
        Object var2 = MockGateway.fieldCall(var0, Desc.getClazz("java.lang.System"), "out", Desc.getType("Ljava/io/PrintStream;"));
        if (var2 == MockGateway.PROCEED) {
            var1 = System.out;
        } else {
            var1 = (PrintStream)var2;
        }

        PrintStream var10000 = var1;
        String var5 = "static init";
        var0 = var10000;
        Object var3 = null;
        if (var0 != null) {
            var3 = var0;
        } else {
            var3 = Desc.getClazz("java.io.PrintStream");
        }

        Object var4 = MockGateway.methodCall(var3, "println", new Object[]{var5}, Desc.getParams("(Ljava/lang/String;)V"), "");
        if (var4 == MockGateway.PROCEED) {
            var0.println(var5);
            var2 = null;
        }
    }
}

如何抑制静态初始化

org.powermock.core.transformers.javassist.SuppressStaticInitializerMockTransformer

通过ClassLoader加载类时，使用ClassTransformer将静态初始化域替换为空方法

Note：这会导致静态Field无法被初始化