解决反射Introspector.getBeanInfo()得到的writeMethodRef与Lombok注解@Accessors(chain = true)冲突导致空指针问题
一、报错信息，空指针异常
java.lang.RuntimeException: java.lang.NullPointerException
at com.bailian.pay.mer.platform.pay.controller.dto.CommonDto.lambda$fromJSON$1(CommonDto.java:61)
at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
at java.util.stream.ReferencePipeline$Head.forEach(ReferencePipeline.java:647)
at com.bailian.pay.mer.platform.pay.controller.dto.CommonDto.fromJSON(CommonDto.java:53)
at com.bailian.pay.mer.platform.pay.service.impl.TransConfigServiceImpl.lambda$main$19(TransConfigServiceImpl.java:1620)
at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
at java.util.ArrayList$Itr.forEachRemaining(ArrayList.java:901)
at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566)
at com.bailian.pay.mer.platform.pay.service.impl.TransConfigServiceImpl.main(TransConfigServiceImpl.java:1634)
Caused by: java.lang.NullPointerException
at com.bailian.pay.mer.platform.pay.controller.dto.CommonDto.lambda$fromJSON$1(CommonDto.java:58)
... 13 more
二、错误解析
1、看哪有异常，定位后发现是json的反序列化出现了空指针异常，用的是自己写的反射逻辑实现
2、一路debug下来发现是 通过json反射为实体类出了问题，p.getWriteMethod()为空导致了空指针问题
/**
* 从JSON 转实体类
*/
@SneakyThrows
public void fromJSON(JSONObject o){
if(o != null){
PropertyDescriptor[] info = beanInfo();
if(info != null){
Arrays.stream(info).forEach(
p -> {
try {
Object value = o.getObject(p.getName(),p.getPropertyType());
if(value != null){
p.getWriteMethod().invoke(this,value);
}
} catch (Exception e) {
throw new RuntimeException(e);
}
}
);
}
}
}
/**
* 通过内省获取bean的所有属性
*/
@SneakyThrows
private PropertyDescriptor[] beanInfo(){
BeanInfo info = Introspector.getBeanInfo(this.getClass());
return info.getPropertyDescriptors();
}
3、进入 getWriteMethod() 方法发现 writeMethodRef 为空
4、那就往上找，发现是 info.getPropertyDescriptors() 的问题，而这个只是个get方法，所以需要看 Introspector.getBeanInfo(Class<?> beanClass) 方法
5、往下debug，发现返回的beanInfo通过了new Introspector(beanClass, null, USE_ALL_BEANINFO).getBeanInfo()方法
6、再往下看发现是getTargetPropertyInfo()返回的writeMethodRef为空
7、进入getTargetPropertyInfo()方法
private PropertyDescriptor[] getTargetPropertyInfo() {
// Check if the bean has its own BeanInfo that will provide
// explicit information.
PropertyDescriptor[] explicitProperties = null;
if (explicitBeanInfo != null) {
explicitProperties = getPropertyDescriptors(this.explicitBeanInfo);
}
if (explicitProperties == null && superBeanInfo != null) {
// We have no explicit BeanInfo properties. Check with our parent.
addPropertyDescriptors(getPropertyDescriptors(this.superBeanInfo));
}
for (int i = 0; i < additionalBeanInfo.length; i++) {
addPropertyDescriptors(additionalBeanInfo[i].getPropertyDescriptors());
}
if (explicitProperties != null) {
// Add the explicit BeanInfo data to our results.
addPropertyDescriptors(explicitProperties);
} else {
// Apply some reflection to the current class.
// First get an array of all the public methods at this level
Method methodList[] = getPublicDeclaredMethods(beanClass);
// Now analyze each method.
for (int i = 0; i < methodList.length; i++) {
Method method = methodList[i];
if (method == null) {
continue;
}
// skip static methods.
int mods = method.getModifiers();
if (Modifier.isStatic(mods)) {
continue;
}
String name = method.getName();
Class<?>[] argTypes = method.getParameterTypes();
Class<?> resultType = method.getReturnType();
int argCount = argTypes.length;
PropertyDescriptor pd = null;
if (name.length() <= 3 && !name.startsWith(IS_PREFIX)) {
// Optimization. Don't bother with invalid propertyNames.
continue;
}
try {
if (argCount == 0) {
if (name.startsWith(GET_PREFIX)) {
// Simple getter
pd = new PropertyDescriptor(this.beanClass, name.substring(3), method, null);
} else if (resultType == boolean.class && name.startsWith(IS_PREFIX)) {
// Boolean getter
pd = new PropertyDescriptor(this.beanClass, name.substring(2), method, null);
}
} else if (argCount == 1) {
if (int.class.equals(argTypes[0]) && name.startsWith(GET_PREFIX)) {
pd = new IndexedPropertyDescriptor(this.beanClass, name.substring(3), null, null, method, null);
} else if (void.class.equals(resultType) && name.startsWith(SET_PREFIX)) {
// Simple setter
pd = new PropertyDescriptor(this.beanClass, name.substring(3), null, method);
if (throwsException(method, PropertyVetoException.class)) {
pd.setConstrained(true);
}
}
} else if (argCount == 2) {
if (void.class.equals(resultType) && int.class.equals(argTypes[0]) && name.startsWith(SET_PREFIX)) {
pd = new IndexedPropertyDescriptor(this.beanClass, name.substring(3), null, null, null, method);
if (throwsException(method, PropertyVetoException.class)) {
pd.setConstrained(true);
}
}
}
} catch (IntrospectionException ex) {
// This happens if a PropertyDescriptor or IndexedPropertyDescriptor
// constructor fins that the method violates details of the deisgn
// pattern, e.g. by having an empty name, or a getter returning
// void , or whatever.
pd = null;
}
if (pd != null) {
// If this class or one of its base classes is a PropertyChange
// source, then we assume that any properties we discover are "bound".
if (propertyChangeSource) {
pd.setBound(true);
}
addPropertyDescriptor(pd);
}
}
}
processPropertyDescriptors();
// Allocate and populate the result array.
PropertyDescriptor result[] =
properties.values().toArray(new PropertyDescriptor[properties.size()]);
// Set the default index.
if (defaultPropertyName != null) {
for (int i = 0; i < result.length; i++) {
if (defaultPropertyName.equals(result[i].getName())) {
defaultPropertyIndex = i;
}
}
}
return result;
}
8、主要看看这两段代码，第一段为获取方法的入参和出参，第二段判断只有入参的参数为一个，返回值是void，且方法名以set作为前缀的，才会被当做writeMethod，即写入方法。
像BeanCopier依赖Introspector的writeMethod对目标类赋值的工具，在转换使用了@Accessors(chain = true)注解的类时，在获取属性描述PropertyDescriptor就不会返回这个属性的writeMethod属性，就相当于该类的属性没有“写入方法”，这就造成了拷贝对象过程中出现空指针问题。
String name = method.getName();
Class<?>[] argTypes = method.getParameterTypes();
Class<?> resultType = method.getReturnType();
else if (argCount == 1) {
if (int.class.equals(argTypes[0]) && name.startsWith(GET_PREFIX)) {
pd = new IndexedPropertyDescriptor(this.beanClass, name.substring(3), null, null, method, null);
} else if (void.class.equals(resultType) && name.startsWith(SET_PREFIX)) {
// Simple setter
pd = new PropertyDescriptor(this.beanClass, name.substring(3), null, method);
if (throwsException(method, PropertyVetoException.class)) {
pd.setConstrained(true);
}
}
}
三、解决方法
1、去掉@Accessors(chain = true)注解
2、使用其他的反序列化手段，比如FastJson
Dto dto = JSON.toJavaObject(json, Dto.class)
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