排查了3个多小时，因为一个简单的错误，发现一个强大的参数解析工具，记录一下。
背景
Nodejs 通过 tether 调用 Java Dubbo 服务。请求类的某个参数对象 EsCondition 有 fieldName, op, value 三个字段，value 的参数值正确解析， fieldName, op 的参数值解析为 null 。 深入到 Dubbo 源码进行单步调试定位到，发现字段 fieldName, op 缺少 setter 方法。 加上之后就正常了。
JavaBean约定
定位到问题后，有一种如梦方醒的感觉。问题就是这么简单，可是却花了很多时间。如果我注意到一个类里有 a, b, c 三个字段， c 解析成功了，有 getter/setter 方法，而 b, c 没有 setter 方法，通过仔细对比或许就可以解决这个问题。
事实上， Java 与框架进行交互有个基本的约定： JavaBean 约定， JavaBean 中的每个实例属性都有 setter/getter 方法。完整的约定如下：
- 有一个 public 默认构造器（尤其要有无参构造器）；
- 属性设置成 private， 使用 public 的 getter，setter 方法访问，同时getter，setter 方法与属性名也需要对应。例如属性 name，getter 方法就要写成
public String getName(){ return name; }。 - 实现序列化接口。
如果缺乏默认构造器，那么在构造 Java 入参对象会有问题； 如果缺失 getter / setter ，在设置或获取入参对象的字段的值就会有问题。事实上，很多框架都使用了反射的方式，通过 getter/setter 方法来操作 JavaBean 中的字段来进行操作。因此，保证 JavaBean 约定，是与众多框架进行交互的重要前提。 而要保证 JavaBean 约定，只要自动生成 setter/getter 方法，或者在类上增加一个 @Getter, @ Setter, 或 @Data 注解即可。JavaBeans 的百科： “JavaBeans”
约定胜于配置。 建立一些约定进行简单处理，往往比灵活而复杂处理各种配置更加容易理解。 读者可阅： “约定优于配置”
PojoUtils
这里有个强大的参数解析类 com.alibaba.dubbo.common.utils.PojoUtils，用于将嵌套的 Map 转换成嵌套的对象。特别实用。PoJoUtils 与 CompatibleTypeUtils, ReflectUtils, ClassHelper 联合实现了这个功能。 这里先给出一个测试用例。
package shared.util;
import com.google.common.collect.ImmutableMap;
import org.junit.Test;
import shared.utils.PojoUtils;
import zzz.study.apidesign.export.common.Condition;
import zzz.study.apidesign.export.common.ExportParam;
import zzz.study.apidesign.export.common.SearchParam;
import zzz.study.patterns.composite.escondition.Match;
import zzz.study.patterns.composite.escondition.Op;
import zzz.study.patterns.composite.escondition.Range;
import java.util.Arrays;
import java.util.Objects;
public class PojoUtilsTest {
@Test
public void testRealize() {
ExportParam exportParam = new ExportParam();
exportParam.setBizType("order");
exportParam.setCategory("baozhengjin");
exportParam.setSource("wsc");
exportParam.setRequestId("request"+System.currentTimeMillis());
exportParam.setExtra(ImmutableMap.of("account", "qin"));
exportParam.setStrategy("standard");
SearchParam searchParam = new SearchParam();
searchParam.setBizId(123L);
searchParam.setStartTime(151456798L);
searchParam.setEndTime(153456789L);
searchParam.setConditions(Arrays.asList(
new Condition("name", Op.eq, "sisi"),
new Condition("pay_time", Op.range, new Range(152987654L, 153987654)),
new Condition("state", Op.in, Arrays.asList(5,6)),
new Condition("goods_title", Op.match, new Match("走过路过不要错过", "100%"))
));
exportParam.setSearch(searchParam);
Object paramGeneralized = PojoUtils.generalize(exportParam);
ExportParam exportParamRestored = (ExportParam) PojoUtils.realize(paramGeneralized, ExportParam.class);
assert Objects.equals(exportParamRestored, exportParam);
}
}
generalize 将一个对象转换成 Map，在 dubbo 服务端，realize 将 Map 还原为对象。
代码实现
读者可以引用 dubbo 2 以上版本，查看 com.alibaba.dubbo.common.utils.PojoUtils 这个类的实现。里面分不同情况进行了解析，同时使用了递归技术来对嵌套的结果进行解析。
/*
* Copyright 1999-2011 Alibaba Group.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.alibaba.dubbo.common.utils;
import java.lang.reflect.Array;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Proxy;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Hashtable;
import java.util.IdentityHashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.TreeMap;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ConcurrentSkipListMap;
/**
* PojoUtils. Travel object deeply, and convert complex type to simple type.
* <p>
* Simple type below will be remained:
* <ul>
* <li> Primitive Type, also include <b>String</b>, <b>Number</b>(Integer, Long), <b>Date</b>
* <li> Array of Primitive Type
* <li> Collection, eg: List, Map, Set etc.
* </ul>
* <p>
* Other type will be covert to a map which contains the attributes and value pair of object.
*
* @author william.liangf
* @author ding.lid
*/
public class PojoUtils {
private static final ConcurrentMap<String, Method> NAME_METHODS_CACHE = new ConcurrentHashMap<String, Method>();
private static final ConcurrentMap<Class<?>, ConcurrentMap<String, Field>> CLASS_FIELD_CACHE =
new ConcurrentHashMap<Class<?>, ConcurrentMap<String, Field>>();
public static Object[] generalize(Object[] objs) {
Object[] dests = new Object[objs.length];
for (int i = 0; i < objs.length; i ++) {
dests[i] = generalize(objs[i]);
}
return dests;
}
public static Object[] realize(Object[] objs, Class<?>[] types) {
if (objs.length != types.length)
throw new IllegalArgumentException("args.length != types.length");
Object[] dests = new Object[objs.length];
for (int i = 0; i < objs.length; i ++) {
dests[i] = realize(objs[i], types[i]);
}
return dests;
}
public static Object[] realize(Object[] objs, Class<?>[] types, Type[] gtypes) {
if (objs.length != types.length
|| objs.length != gtypes.length)
throw new IllegalArgumentException("args.length != types.length");
Object[] dests = new Object[objs.length];
for (int i = 0; i < objs.length; i ++) {
dests[i] = realize(objs[i], types[i], gtypes[i]);
}
return dests;
}
public static Object generalize(Object pojo) {
return generalize(pojo, new IdentityHashMap<Object, Object>());
}
@SuppressWarnings("unchecked")
private static Object generalize(Object pojo, Map<Object, Object> history) {
if (pojo == null) {
return null;
}
if (pojo instanceof Enum<?>) {
return ((Enum<?>)pojo).name();
}
if (pojo.getClass().isArray()
&& Enum.class.isAssignableFrom(
pojo.getClass().getComponentType())) {
int len = Array.getLength(pojo);
String[] values = new String[len];
for (int i = 0; i < len; i ++) {
values[i] = ((Enum<?>)Array.get(pojo, i)).name();
}
return values;
}
if (ReflectUtils.isPrimitives(pojo.getClass())) {
return pojo;
}
if (pojo instanceof Class) {
return ((Class)pojo).getName();
}
Object o = history.get(pojo);
if(o != null){
return o;
}
history.put(pojo, pojo);
if (pojo.getClass().isArray()) {
int len = Array.getLength(pojo);
Object[] dest = new Object[len];
history.put(pojo, dest);
for (int i = 0; i < len; i ++) {
Object obj = Array.get(pojo, i);
dest[i] = generalize(obj, history);
}
return dest;
}
if (pojo instanceof Collection<?>) {
Collection<Object> src = (Collection<Object>)pojo;
int len = src.size();
Collection<Object> dest = (pojo instanceof List<?>) ? new ArrayList<Object>(len) : new HashSet<Object>(len);
history.put(pojo, dest);
for (Object obj : src) {
dest.add(generalize(obj, history));
}
return dest;
}
if (pojo instanceof Map<?, ?>) {
Map<Object, Object> src = (Map<Object, Object>)pojo;
Map<Object, Object> dest= createMap(src);
history.put(pojo, dest);
for (Map.Entry<Object, Object> obj : src.entrySet()) {
dest.put(generalize(obj.getKey(), history), generalize(obj.getValue(), history));
}
return dest;
}
Map<String, Object> map = new HashMap<String, Object>();
history.put(pojo, map);
map.put("class", pojo.getClass().getName());
for (Method method : pojo.getClass().getMethods()) {
if (ReflectUtils.isBeanPropertyReadMethod(method)) {
try {
map.put(ReflectUtils.getPropertyNameFromBeanReadMethod(method),
generalize(method.invoke(pojo), history));
} catch (Exception e) {
throw new RuntimeException(e.getMessage(), e);
}
}
}
// public field
for(Field field : pojo.getClass().getFields()) {
if (ReflectUtils.isPublicInstanceField(field)) {
try {
Object fieldValue = field.get(pojo);
// public filed同时也有get/set方法，如果get/set存取的不是前面那个 public field 该如何处理
if (history.containsKey(pojo)) {
Object pojoGenerilizedValue = history.get(pojo);
if (pojoGenerilizedValue instanceof Map
&& ((Map)pojoGenerilizedValue).containsKey(field.getName())) {
continue;
}
}
if (fieldValue != null) {
map.put(field.getName(), generalize(fieldValue, history));
}
} catch (Exception e) {
throw new RuntimeException(e.getMessage(), e);
}
}
}
return map;
}
public static Object realize(Object pojo, Class<?> type) {
return realize0(pojo, type, null , new IdentityHashMap<Object, Object>());
}
public static Object realize(Object pojo, Class<?> type, Type genericType) {
return realize0(pojo, type, genericType, new IdentityHashMap<Object, Object>());
}
private static class PojoInvocationHandler implements InvocationHandler {
private Map<Object, Object> map;
public PojoInvocationHandler(Map<Object, Object> map) {
this.map = map;
}
@SuppressWarnings("unchecked")
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (method.getDeclaringClass() == Object.class) {
return method.invoke(map, args);
}
String methodName = method.getName();
Object value = null;
if (methodName.length() > 3 && methodName.startsWith("get")) {
value = map.get(methodName.substring(3, 4).toLowerCase() + methodName.substring(4));
} else if (methodName.length() > 2 && methodName.startsWith("is")) {
value = map.get(methodName.substring(2, 3).toLowerCase() + methodName.substring(3));
} else {
value = map.get(methodName.substring(0, 1).toLowerCase() + methodName.substring(1));
}
if (value instanceof Map<?,?> && ! Map.class.isAssignableFrom(method.getReturnType())) {
value = realize0((Map<String, Object>) value, method.getReturnType(), null, new IdentityHashMap<Object, Object>());
}
return value;
}
}
@SuppressWarnings("unchecked")
private static Collection<Object> createCollection(Class<?> type, int len) {
if (type.isAssignableFrom(ArrayList.class)) {
return new ArrayList<Object>(len);
}
if (type.isAssignableFrom(HashSet.class)) {
return new HashSet<Object>(len);
}
if (! type.isInterface() && ! Modifier.isAbstract(type.getModifiers())) {
try {
return (Collection<Object>) type.newInstance();
} catch (Exception e) {
// ignore
}
}
return new ArrayList<Object>();
}
private static Map createMap(Map src) {
Class<? extends Map> cl = src.getClass();
Map result = null;
if (HashMap.class == cl) {
result = new HashMap();
} else if (Hashtable.class == cl) {
result = new Hashtable();
} else if (IdentityHashMap.class == cl) {
result = new IdentityHashMap();
} else if (LinkedHashMap.class == cl) {
result = new LinkedHashMap();
} else if (Properties.class == cl) {
result = new Properties();
} else if (TreeMap.class == cl) {
result = new TreeMap();
} else if (WeakHashMap.class == cl) {
return new WeakHashMap();
} else if (ConcurrentHashMap.class == cl) {
result = new ConcurrentHashMap();
} else if (ConcurrentSkipListMap.class == cl) {
result = new ConcurrentSkipListMap();
} else {
try {
result = cl.newInstance();
} catch (Exception e) { /* ignore */ }
if (result == null) {
try {
Constructor<?> constructor = cl.getConstructor(Map.class);
result = (Map)constructor.newInstance(Collections.EMPTY_MAP);
} catch (Exception e) { /* ignore */ }
}
}
if (result == null) {
result = new HashMap<Object, Object>();
}
return result;
}
@SuppressWarnings({ "unchecked", "rawtypes" })
private static Object realize0(Object pojo, Class<?> type, Type genericType, final Map<Object, Object> history) {
if (pojo == null) {
return null;
}
if (type != null && type.isEnum()
&& pojo.getClass() == String.class) {
return Enum.valueOf((Class<Enum>)type, (String)pojo);
}
if (ReflectUtils.isPrimitives(pojo.getClass())
&& ! (type != null && type.isArray()
&& type.getComponentType().isEnum()
&& pojo.getClass() == String[].class)) {
return CompatibleTypeUtils.compatibleTypeConvert(pojo, type);
}
Object o = history.get(pojo);
if(o != null){
return o;
}
history.put(pojo, pojo);
if (pojo.getClass().isArray()) {
if (Collection.class.isAssignableFrom(type)) {
Class<?> ctype = pojo.getClass().getComponentType();
int len = Array.getLength(pojo);
Collection dest = createCollection(type, len);
history.put(pojo, dest);
for (int i = 0; i < len; i ++) {
Object obj = Array.get(pojo, i);
Object value = realize0(obj, ctype, null, history);
dest.add(value);
}
return dest;
} else {
Class<?> ctype = (type != null && type.isArray() ? type.getComponentType() : pojo.getClass().getComponentType());
int len = Array.getLength(pojo);
Object dest = Array.newInstance(ctype, len);
history.put(pojo, dest);
for (int i = 0; i < len; i ++) {
Object obj = Array.get(pojo, i);
Object value = realize0(obj, ctype, null, history);
Array.set(dest, i, value);
}
return dest;
}
}
if (pojo instanceof Collection<?>) {
if (type.isArray()) {
Class<?> ctype = type.getComponentType();
Collection<Object> src = (Collection<Object>)pojo;
int len = src.size();
Object dest = Array.newInstance(ctype, len);
history.put(pojo, dest);
int i = 0;
for (Object obj : src) {
Object value = realize0(obj, ctype, null, history);
Array.set(dest, i, value);
i ++;
}
return dest;
} else {
Collection<Object> src = (Collection<Object>)pojo;
int len = src.size();
Collection<Object> dest = createCollection(type, len);
history.put(pojo, dest);
for (Object obj : src) {
Type keyType = getGenericClassByIndex(genericType, 0);
Class<?> keyClazz = obj.getClass() ;
if ( keyType instanceof Class){
keyClazz = (Class<?>)keyType;
}
Object value = realize0(obj, keyClazz, keyType, history);
dest.add(value);
}
return dest;
}
}
if (pojo instanceof Map<?, ?> && type != null) {
Object className = ((Map<Object, Object>)pojo).get("class");
if (className instanceof String) {
try {
type = ClassHelper.forName((String)className);
} catch (ClassNotFoundException e) {
// ignore
}
}
Map<Object, Object> map ;
// 返回值类型不是方法签名类型的子集 并且 不是接口类型
if (!type.isInterface() && !type.isAssignableFrom(pojo.getClass())) {
try {
map = (Map<Object, Object>) type.newInstance();
Map<Object, Object> mapPojo = (Map<Object, Object>) pojo;
map.putAll(mapPojo);
map.remove("class");
} catch (Exception e) {
//ignore error
map = (Map<Object, Object>)pojo;
}
}else {
map = (Map<Object, Object>)pojo;
}
if (Map.class.isAssignableFrom(type) || type == Object.class) {
final Map<Object, Object> result = createMap(map);
history.put(pojo, result);
for (Map.Entry<Object, Object> entry : map.entrySet()) {
Type keyType = getGenericClassByIndex(genericType, 0);
Type valueType = getGenericClassByIndex(genericType, 1);
Class<?> keyClazz;
if ( keyType instanceof Class){
keyClazz = (Class<?>)keyType;
} else {
keyClazz = entry.getKey() == null ? null : entry.getKey().getClass();
}
Class<?> valueClazz;
if ( valueType instanceof Class){
valueClazz = (Class<?>)valueType;
} else {
valueClazz = entry.getValue() == null ? null : entry.getValue().getClass() ;
}
Object key = keyClazz == null ? entry.getKey() : realize0(entry.getKey(), keyClazz, keyType, history);
Object value = valueClazz == null ? entry.getValue() : realize0(entry.getValue(), valueClazz, valueType, history);
result.put(key, value);
}
return result;
} else if (type.isInterface()) {
Object dest = Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), new Class<?>[]{type}, new PojoInvocationHandler(map));
history.put(pojo, dest);
return dest;
} else {
Object dest = newInstance(type);
history.put(pojo, dest);
for (Map.Entry<Object, Object> entry : map.entrySet()) {
Object key = entry.getKey();
if (key instanceof String) {
String name = (String) key;
Object value = entry.getValue();
if (value != null) {
Method method = getSetterMethod(dest.getClass(), name, value.getClass());
Field field = getField(dest.getClass(), name);
if (method != null) {
if (! method.isAccessible())
method.setAccessible(true);
Type ptype = method.getGenericParameterTypes()[0];
value = realize0(value, method.getParameterTypes()[0], ptype, history);
try {
method.invoke(dest, value);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException("Failed to set pojo " + dest.getClass().getSimpleName() + " property " + name
+ " value " + value + "(" + value.getClass() + "), cause: " + e.getMessage(), e);
}
} else if (field != null) {
value = realize0(value, field.getType(), field.getGenericType(), history);
try {
field.set(dest, value);
} catch (IllegalAccessException e) {
throw new RuntimeException(
new StringBuilder(32)
.append("Failed to set filed ")
.append(name)
.append(" of pojo ")
.append(dest.getClass().getName())
.append( " : " )
.append(e.getMessage()).toString(),
e);
}
}
}
}
}
if (dest instanceof Throwable) {
Object message = map.get("message");
if (message instanceof String) {
try {
Field filed = Throwable.class.getDeclaredField("detailMessage");
if(! filed.isAccessible()) {
filed.setAccessible(true);
}
filed.set(dest, (String) message);
} catch (Exception e) {
}
}
}
return dest;
}
}
return pojo;
}
/**
* 获取范型的类型
* @param genericType
* @param index
* @return List<Person> 返回Person.class ,Map<String,Person> index=0 返回String.class index=1 返回Person.class
*/
private static Type getGenericClassByIndex(Type genericType, int index){
Type clazz = null ;
//范型参数转换
if (genericType instanceof ParameterizedType){
ParameterizedType t = (ParameterizedType)genericType;
Type[] types = t.getActualTypeArguments();
clazz = types[index];
}
return clazz;
}
private static Object newInstance(Class<?> cls) {
try {
return cls.newInstance();
} catch (Throwable t) {
try {
Constructor<?>[] constructors = cls.getConstructors();
if (constructors != null && constructors.length == 0) {
throw new RuntimeException("Illegal constructor: " + cls.getName());
}
Constructor<?> constructor = constructors[0];
if (constructor.getParameterTypes().length > 0) {
for (Constructor<?> c : constructors) {
if (c.getParameterTypes().length <
constructor.getParameterTypes().length) {
constructor = c;
if (constructor.getParameterTypes().length == 0) {
break;
}
}
}
}
return constructor.newInstance(new Object[constructor.getParameterTypes().length]);
} catch (InstantiationException e) {
throw new RuntimeException(e.getMessage(), e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e.getMessage(), e);
} catch (InvocationTargetException e) {
throw new RuntimeException(e.getMessage(), e);
}
}
}
private static Method getSetterMethod(Class<?> cls, String property, Class<?> valueCls) {
String name = "set" + property.substring(0, 1).toUpperCase() + property.substring(1);
Method method = NAME_METHODS_CACHE.get(cls.getName() + "." + name + "(" +valueCls.getName() + ")");
if(method == null){
try {
method = cls.getMethod(name, valueCls);
} catch (NoSuchMethodException e) {
for (Method m : cls.getMethods()) {
if (ReflectUtils.isBeanPropertyWriteMethod(m)
&& m.getName().equals(name)) {
method = m;
}
}
}
if(method != null){
NAME_METHODS_CACHE.put(cls.getName() + "." + name + "(" +valueCls.getName() + ")", method);
}
}
return method;
}
private static Field getField(Class<?> cls, String fieldName) {
Field result = null;
if (CLASS_FIELD_CACHE.containsKey(cls)
&& CLASS_FIELD_CACHE.get(cls).containsKey(fieldName)) {
return CLASS_FIELD_CACHE.get(cls).get(fieldName);
}
try {
result = cls.getField(fieldName);
} catch (NoSuchFieldException e) {
for(Field field : cls.getFields()) {
if (fieldName.equals(field.getName())
&& ReflectUtils.isPublicInstanceField(field)) {
result = field;
break;
}
}
}
if (result != null) {
ConcurrentMap<String, Field> fields = CLASS_FIELD_CACHE.get(cls);
if (fields == null) {
fields = new ConcurrentHashMap<String, Field>();
CLASS_FIELD_CACHE.putIfAbsent(cls, fields);
}
fields = CLASS_FIELD_CACHE.get(cls);
fields.putIfAbsent(fieldName, result);
}
return result;
}
public static boolean isPojo(Class<?> cls) {
return ! ReflectUtils.isPrimitives(cls)
&& ! Collection.class.isAssignableFrom(cls)
&& ! Map.class.isAssignableFrom(cls);
}
}