要模拟的类：
public class PrivateObject {
private String privateString;
public PrivateObject(String privateString) {
this.privateString = privateString;
}
private String getPrivateString() {
return this.privateString;
}
}
使用PowerMock模拟：
// 类实例（class instance）
PrivateObject instance = new PrivateObject ();
// 模拟私有字段/变量（private field/variable）
MemberModifier
.field(PrivateObject .class, "privateString").set(
instance , "hellomock");
// 模拟私有方法（private method）
MemberModifier
.stub(MemberMatcher.method(PrivateObject .class,
"getPrivateString"))
.toReturn(
"Power Mock");
