Java8-Guava實戰示例

 

示例一：

跟示例三對比一下，儘可能用示例三

List<InvoiceQueryBean> invoiceQueryBeanList = new ArrayList<>();
List<String> invoices = Lists.newArrayList(Iterators.transform(
        invoiceQueryBeanList.iterator(), new Function<InvoiceQueryBean, String>() {
    @Nullable
    @Override
    public String apply(@Nullable InvoiceQueryBean input) {
        if (StringUtils.isNotBlank(input.getLoanInvoiceId())) {
            return input.getLoanInvoiceId();
        } else {
            return null;
        }
    }
}));
//去除空的
Iterators.removeIf(invoices.iterator(), StringUtils::isBlank);

示例二：

public static List<PersonLoanInvoiceQueryPojo> getInvoiceQueryPojoList(List<InvoiceQueryBean> invoiceQueryBean) {
    return Lists.newArrayList(Iterators.transform(invoiceQueryBean.iterator(),
            input -> input == null ? null :
                    PersonLoanInvoiceQueryPojo.Builder.getInstance()
                            .addLoanInvoiceId(input.getLoanInvoiceId())
                            .addUserName(input.getUserName())
                            .addCertificateKind(input.getCertificateKind())
                            .addCertificateNo(input.getCertificateNo()).addProductName(input.getProductName())
                            .addMerchantName(input.getMerchantName())
                            .addStoreName(input.getStoreName())
                            .addApplyDate(input.getApplyDate()).addLoanAmount(input.getLoanAmount())
                            .addLoanPeriod(input.getLoanPeriod()).addLoanPurpose(input.getLoanPurpose())
                            .addLoanDate(input.getLoanDate()).addRate(input.getRate())
                            .addChannelNo(input.getChannelNo())
                            .addApproveDate(input.getApproveDate())
                            .addReply(input.getReply())
                            .addMarketingCenterId(input.getMarketingCenterId()).build()));
}

public class PersonLoanInvoiceQueryPojo implements Serializable{
    
    private static final long serialVersionUID = -408985049449365784L;

    private String loanInvoiceId;
    
    private String userId;
    
    private String userName;

    public static class Builder {
        private PersonLoanInvoiceQueryPojo instance = new PersonLoanInvoiceQueryPojo();

        private Builder(){}

        public static Builder getInstance() {
            return new Builder();
        }

        public static Builder getInstance(PersonLoanInvoiceQueryPojo instance){
            Builder builder = new Builder();
            builder.instance = instance;
            return builder;
        }

        public Builder addLoanInvoiceId(String loanInvoiceId) {
            this.instance.setLoanInvoiceId(loanInvoiceId);
            return this;
        }

        public Builder addUserId(String userId) {
            this.instance.setUserId(userId);
            return this;
        }

        public Builder addUserName(String userName) {
            this.instance.setUserName(userName);
            return this;
        }

        public PersonLoanInvoiceQueryPojo build() {
            return this.instance;
        }

    }
    
    setters();&getters();
}

 示例三：方法引用

　　方法引用主要有三類：

　　　　（1）指向靜態方法的方法引用，（例如：Integer中的parseInt方法，寫做Integer::parseInt）

　　　　（2）指向任意類型實例方法的方法引用（例如String中的length方法，寫做String::length）

　　　　（3）指向現有對象的實例方法的方法引用（以下例）

import com.google.common.collect.Iterators;
import com.google.common.collect.Lists;

List<CreditPersonalInfoChangeApplySerial> applySerialList = new ArrayList<>();
List<String> operatorNoList = Lists.newArrayList(
            Iterators.transform(applySerialList.iterator(), CreditPersonalInfoChangeApplySerial::getOperatorNo)); //這個叫作lambda的方法引用，注意方法引用的這個方法不須要()

 示例四：

　　Lambad將List轉換成Map

import com.google.common.collect.Maps;

List<QueryUserAppInfoByUserIdListPojo> operatorInfoList = new ArrayList<>();
Map<String, QueryUserAppInfoByUserIdListPojo> operatorMap
            = Maps.uniqueIndex(operatorInfoList.iterator(), QueryUserAppInfoByUserIdListPojo::getUserId);
            
public class QueryUserAppInfoByUserIdListPojo implements Serializable {
    private static final long serialVersionUID = 6876288995978264269L;
    private String userId;
    
    public String getUserId() {
        return this.userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

}

 示例五：

List<UserPojo> list =  new ArrayList<>();
list.forEach(input -> {
    if (input.getCertificateKind().equals(EnumCertificateKind.RESIDENT_IDENTITY_CARD)) {
        userCertificateMap.put(pojo.getUserId(), input);
    }
});

 示例六：

　　遍歷的時候須要使用到元素的索引，很惋惜，Java8 的 Iterable 並無提供一個帶索引的 forEach 方法，自動動手寫一個知足本身的需求。

import java.util.Objects;
import java.util.function.BiConsumer;

/**
 * Iterable 的工具類
 */
public class Iterables {

    public static <E> void forEach(
            Iterable<? extends E> elements, BiConsumer<Integer, ? super E> action) {
        Objects.requireNonNull(elements);
        Objects.requireNonNull(action);

        int index = 0;
        for (E element : elements) {
            action.accept(index++, element);
        }
    }
}

 

public static void main(String[] args) throws Exception {

    List<String> list = Arrays.asList("a", "b", "b", "c", "c", "c", "d", "d", "d", "f", "f", "g");

    Iterables.forEach(list, (index, str) -> System.out.println(index + " -> " + str));
}

 示例七：Iterators.find

注意：find()函數有兩個重載方法，其中一個是帶 defaultValue 的，注意若是別迭代的集合沒有符合條件的數據的話，必定要定義一個默認值。不然會報NoSuchElementException異常

Iterators.find(pojoList.iterator(), input -> input != null, null);

 

參考：