Web3j 继承StaticStruct的类所有属性必须为Public，属性的顺序和数量必须和solidity 里面的struct 属性相同，否则属性少了或者多了的时候会出现错位

Web3j 继承StaticStruct的类所有属性不能为private，因为web3j 是通过长度去截取返回值解析成对应的属性进行赋值的。要获取一个list对象时，web3j是按一个类的所有public属性个数去截取总长度的，再进行解析赋值到没一个属性里

StaticStruct类

import lombok.Data;
import org.web3j.abi.datatypes.Address;
import org.web3j.abi.datatypes.StaticStruct;
import org.web3j.abi.datatypes.Type;
import org.web3j.abi.datatypes.generated.Uint256;@Data
public class ChildStaticStruct extends StaticStruct {public Uint256 attr1;public Uint256 attr2;public Address attr3;public ChildStaticStruct(Uint256 attr1, Uint256 attr2, Address attr3) {super(new Type[]{attr1,attr2,attr3});}
}

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.web3j.abi.FunctionEncoder;
import org.web3j.abi.FunctionReturnDecoder;
import org.web3j.abi.TypeReference;
import org.web3j.abi.datatypes.Address;
import org.web3j.abi.datatypes.DynamicArray;
import org.web3j.abi.datatypes.Function;
import org.web3j.abi.datatypes.Type;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.DefaultBlockParameterName;
import org.web3j.protocol.core.methods.request.Transaction;
import org.web3j.protocol.core.methods.response.EthCall;import java.io.IOException;
import java.util.Arrays;
import java.util.List;public class TestContract {private static final Logger logger = LoggerFactory.getLogger(TestContract.class);private String address;private Web3j web3j;public TestContract(String address, Web3j web3j) {this.address = address;this.web3j = web3j;}public List<ChildStaticStruct> getStaticStructList(String address) throws IOException {List<Type> inputParameters = Arrays.asList( new Address(address));List<TypeReference<?>> outputParameters = Arrays.asList(new TypeReference<DynamicArray<ChildStaticStruct>>(){});Function function = new Function("getStaticStructList",inputParameters,outputParameters);Transaction transaction = Transaction.createEthCallTransaction(null,address, FunctionEncoder.encode(function));EthCall response = web3j.ethCall(transaction, DefaultBlockParameterName.LATEST).send();List<Type> output = FunctionReturnDecoder.decode(response.getValue(),function.getOutputParameters());List<ChildStaticStruct> results = (List<ChildStaticStruct>)output.get(0).getValue();return results;}
}

web3j的TypeDecoder 里的decodeArrayElements 验证了是否为StructType子类，

在currOffset += getSingleElementLength(input, currOffset, cls) * 64)判断了截取的长度

if (StructType.class.isAssignableFrom(cls)) {elements = new ArrayList(length);currOffset = 0;for(currOffset = offset; currOffset < length; currOffset += getSingleElementLength(input, currOffset, cls) * 64) {if (DynamicStruct.class.isAssignableFrom(cls)) {value = decodeDynamicStruct(input, offset + DefaultFunctionReturnDecoder.getDataOffset(input, currOffset, typeReference), TypeReference.create(cls));} else {value = decodeStaticStruct(input, currOffset, TypeReference.create(cls));}elements.add(value);++currOffset;}String typeName = Utils.getSimpleTypeName(cls);return (Type)consumer.apply(elements, typeName);} 

getSingleElementLength 验证了截取长度是根据public属性数量去截取Utils.staticStructNestedPublicFieldsFlatList(type).size()，pirvate计算长度

static <T extends Type> int getSingleElementLength(String input, int offset, Class<T> type) {if (input.length() == offset) {return 0;} else if (!DynamicBytes.class.isAssignableFrom(type) && !Utf8String.class.isAssignableFrom(type)) {return StaticStruct.class.isAssignableFrom(type) ? Utils.staticStructNestedPublicFieldsFlatList(type).size() : 1;} else {return decodeUintAsInt(input, offset) / 32 + 2;}}

 staticStructNestedPublicFieldsFlatList方面里面通过Modifier.isPublic(field.getModifiers())过滤了public  

public static List<Field> staticStructNestedPublicFieldsFlatList(Class<Type> classType) {return (List)staticStructsNestedFieldsFlatList(classType).stream().filter((field) -> {return Modifier.isPublic(field.getModifiers());}).collect(Collectors.toList());}

Modifier 里面比较了Public

public static boolean isPublic(int mod) {return (mod & PUBLIC) != 0;}