Lambda多条件分组（实战）

最新推荐文章于 2025-05-23 10:05:52 发布

tian.tian

最新推荐文章于 2025-05-23 10:05:52 发布

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本文链接：https://blog.youkuaiyun.com/li_tiantian/article/details/103850632

本文通过两个示例详细介绍了如何使用Lambda表达式在Java中进行多条件的实体类分组操作，涵盖从实体类定义到具体分组逻辑的实现过程。

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一、实体类

import java.io.Serializable;
import lombok.Data;

@Data
public class ReceiptApply implements Serializable {
	private Integer billCode; // 订单号
	private String receiptName; // 收款人姓名
	private String bankName; // 收款银行
	private String receiptAccountNumber; // 收款账号
	private Integer money; // 收款金额
	private Byte isDeleted;
}


import java.io.Serializable;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data                              //get，set
@NoArgsConstructor                 //无参构造
@AllArgsConstructor                //有参构造
public class ReceiptBankInfo implements Serializable {
	private String receiptName; // 收款人姓名
	private String bankName; // 收款银行
	private String receiptAccountNumber; // 收款账号
}

二、示例一

import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.toList;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.List;
import org.junit.Test;
import com.alibaba.fastjson.JSON;

public class LambdaGroupByTest {

	@Test
	public void groupByTest() {
        // 简单条件分组
        Map<String, List<ReceiptApply>> map = exportUrlBeans.stream()
                             .collect(groupingBy(ReceiptApply::getReceiptAccountNum));

		// 按 收款人姓名、收款银行、收款账号 分组
		HashMap<ReceiptBankInfo, List<ReceiptApply>> map = getReceiptApplys().stream()
				.collect(groupingBy(d -> new ReceiptBankInfo(d.getReceiptName(), d.getBankName(), d.getReceiptAccountNumber()),
				HashMap::new, toList()));
		
		System.out.println(JSON.toJSONString(map));
	}
	
	// 注意：返回 Collection，不要返回List
	private Collection<ReceiptApply> getReceiptApplys() {
		Collection<ReceiptApply> receiptApplys = new ArrayList<>();
		receiptApplys.add(getReceiptApplys(10001, "张三", "中国建设银行", "receiptAccountNumber0001", 100, (byte) 0));
		receiptApplys.add(getReceiptApplys(10002, "张三", "中国建设银行", "receiptAccountNumber0001", 200, (byte) 0));
		receiptApplys.add(getReceiptApplys(10003, "张三", "中国建设银行", "receiptAccountNumber0001", 300, (byte) 0));
		receiptApplys.add(getReceiptApplys(10004, "李四", "工商银行", "receiptAccountNumber0002", 100, (byte) 0));
		receiptApplys.add(getReceiptApplys(10005, "李四", "工商银行", "receiptAccountNumber0002", 200, (byte) 0));
		return receiptApplys;
	}

	private ReceiptApply getReceiptApplys(Integer billCode, String receiptName, String bankName, String receiptAccountNumber, Integer money, Byte isDeleted) {
		ReceiptApply receiptApply = new ReceiptApply();
		receiptApply.setBillCode(billCode);
		receiptApply.setReceiptName(receiptName);
		receiptApply.setBankName(bankName);
		receiptApply.setReceiptAccountNumber(receiptAccountNumber);
		receiptApply.setMoney(money);
		receiptApply.setIsDeleted(isDeleted);
		return receiptApply;
	}
}

三、示例二

import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.toList;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import org.junit.Test;
import com.alibaba.fastjson.JSON;

public class LambdaGroupByTest {

	@Test
	public void groupByTest1() {
		// 按 收款人姓名、收款银行、收款账号 分组
		HashMap<String, List<ReceiptApply>> map = getReceiptApplys().stream()
				.collect(groupingBy(d -> JSON.toJSONString(new ReceiptBankInfo(d.getReceiptName(), d.getBankName(), d.getReceiptAccountNumber())),
				HashMap::new, toList()));
		// map的key为什么转成String，因为 new一个对象，即使所有属性都相同，但是地址的引用不同，即map的key不同
		
		Map<ReceiptBankInfo, List<ReceiptApply>> resultMap = new HashMap<>();
		for (Map.Entry<String, List<ReceiptApply>> entry : map.entrySet()) {
			ReceiptBankInfo bankInfo = JSON.parseObject(entry.getKey(), ReceiptBankInfo.class);
			resultMap.put(bankInfo, entry.getValue());
		}
		
		System.out.println(JSON.toJSONString(map));
		System.out.println(JSON.toJSONString(resultMap));
	}
	
	private List<ReceiptApply> getReceiptApplys() {
		List<ReceiptApply> receiptApplys = new ArrayList<>();
		receiptApplys.add(getReceiptApplys(10001, "张三", "中国建设银行", "receiptAccountNumber0001", 100, (byte) 0));
		receiptApplys.add(getReceiptApplys(10002, "张三", "中国建设银行", "receiptAccountNumber0001", 200, (byte) 0));
		receiptApplys.add(getReceiptApplys(10003, "张三", "中国建设银行", "receiptAccountNumber0001", 300, (byte) 0));
		receiptApplys.add(getReceiptApplys(10004, "李四", "工商银行", "receiptAccountNumber0002", 100, (byte) 0));
		receiptApplys.add(getReceiptApplys(10005, "李四", "工商银行", "receiptAccountNumber0002", 200, (byte) 0));
		return receiptApplys;
	}

	private ReceiptApply getReceiptApplys(Integer billCode, String receiptName, String bankName, String receiptAccountNumber, Integer money, Byte isDeleted) {
		ReceiptApply receiptApply = new ReceiptApply();
		receiptApply.setBillCode(billCode);
		receiptApply.setReceiptName(receiptName);
		receiptApply.setBankName(bankName);
		receiptApply.setReceiptAccountNumber(receiptAccountNumber);
		receiptApply.setMoney(money);
		receiptApply.setIsDeleted(isDeleted);
		return receiptApply;
	}
}