objenesis是一个小型java类库用来实例化一个特定class的对象。
使用objenesis实例化对象
static class City {
private String code;
public City(String code) {
super();
this.code = code;
}
}
@Test
public void test02() {
Objenesis objenesis = new ObjenesisStd();
ObjectInstantiator<City> instantiator = objenesis.getInstantiatorOf(City.class);
City city = instantiator.newInstance();
System.out.println(city);
System.out.println(city.code);
}
执行结果
com.springframework.chapter34.App$City@726f3b58
null
使用JDK自带的Class实例化对象
@Test
public void test03() {
Class<City> clazz = City.class;
try {
City city = clazz.newInstance();
} catch (InstantiationException | IllegalAccessException e) {
e.printStackTrace();
}
}
执行结果
java.lang.InstantiationException: com.springframework.chapter34.App$City
at java.lang.Class.newInstance(Class.java:427)
at com.springframework.chapter34.App.test03(App.java:57)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:538)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:760)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:460)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:206)
Caused by: java.lang.NoSuchMethodException: com.springframework.chapter34.App$City.<init>()
at java.lang.Class.getConstructor0(Class.java:3082)
at java.lang.Class.newInstance(Class.java:412)
... 24 mor
Objenesis Vs class.newInstance
从以上代码可以发现class构造器需要参数,而Objenesis可以绕过去, Objenesis主要应用场景:
1. 序列化,远程调用和持久化 -对象需要实例化并存储为到一个特殊的状态,而没有调用代码。
2. 代理,AOP库和Mock对象 -类可以被子类继承而子类不用担心父类的构造器。
3. 容器框架 -对象可以以非标准的方式被动态实例化。
引自:不使用构造方法创建Java对象: objenesis的基本使用方法