Java分析Lambda表达式Stream流合并分组内对象数据合并

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.18</version>
        </dependency>
        <dependency>
            <groupId>cn.hutool</groupId>
            <artifactId>hutool-core</artifactId>
            <version>5.5.6</version>
        </dependency>
    </dependencies>

package com.leo;
import lombok.Data;
import java.io.Serializable;
@Data
public class TestObj implements Serializable {
    private static final long serialVersionUID = 1L;
    String provinceId;
    String field1;
    String field2;
    String field3;
    String field4;
    String field5;
    String field6;
    String field7;
    String field8;
    String field9;
}

    /**
     * 测试类
     */
    @Test
    public void streamConcat2() {
        TestObj t0 = new TestObj();
        t0.setProvinceId("000");
        t0.setField1("1");
        t0.setField2("2");
        t0.setField3("3");
        TestObj t1 = new TestObj();
        t1.setProvinceId("100");
        t1.setField1("1");
        t1.setField2("2");
        t1.setField3("3");
        TestObj t2 = new TestObj();
        t2.setProvinceId("100");
        t2.setField4("4");
        t2.setField5("5");
        t2.setField6("6");
        TestObj t3 = new TestObj();
        t3.setProvinceId("100");
        t3.setField7("7");
        t3.setField8("8");
        t3.setField9("9");
        TestObj t4 = new TestObj();
        t4.setProvinceId("102");
        t4.setField7("7");
        t4.setField8("8");
        t4.setField9("9");
        List<TestObj> list1 = new ArrayList<>();
        list1.add(t0);
        list1.add(t1);
        List<TestObj> list2 = new ArrayList<>();
        list2.add(t2);
        List<TestObj> list3 = new ArrayList<>();
        list3.add(t3);
        list3.add(t4);
        // 根据省份id进行分组，将同一个省的不同字段合并成一条数据对象
        List<TestObj> list = Stream.concat(Stream.concat(list1.stream(), list2.stream()), list3.stream())
                .filter(e -> e != null)
                .collect(Collectors.toMap(TestObj::getProvinceId, a -> a, (o1, o2) -> {
                    try {
                        // Hutool 的属性拷贝，最后一个参数是设置为null的字段不拷贝
                        BeanUtil.copyProperties(o1, o2, CopyOptions.create().setIgnoreNullValue(true).setIgnoreError(true));
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return o2;
                })).values().stream().collect(Collectors.toList());
        // 打印数据
        list.stream().forEach(System.out::println);
    }
}