Question

我有一个属性很少的A类：

class A {

private String col1;
private String col2;
private List<B> bList;

// setters and getters
}

Class B {
private String b1;
private String b2;
//setters and getters
}

我正在尝试使用supercsv和dozer将其写入csv文件。

csv应该与A类列表bList中的元素具有相同的行数。并且应该有四列col1，col2（对于所有行都是通用的）和b1，b2来自A类中的B类列表。

目前我在映射文件中有：

<mapping type="one-way" wildcard="false" map-null="true">
                <class-a>package.a</class-a>
                <class-b>org.supercsv.io.dozer.CsvDozerBeanData</class-b>
.....
</mapping>

但它只将数据映射到一行。如果不将它映射到更平坦的类中，那么更好的方法是什么。在映射中可以将它从A类映射到CsvDozerBeanData列表？那会有用吗？

感谢。

Answer 1

您可以将B的关系添加回A吗？然后，您可以使用以下bean映射迭代每个子项列表：

new String[] { "a.col1", "a.col2", "b1", "b2" }

以下是您如何使用此功能的示例。请注意嵌套循环迭代每个B内的每个A。

public class DozerTest {

    @Test
    public final void test() throws IOException {
        StringWriter out = new StringWriter();
        ICsvDozerBeanWriter writer = new CsvDozerBeanWriter(out, 
                CsvPreference.STANDARD_PREFERENCE);
        writer.configureBeanMapping(B.class, 
                new String[] { "a.col1", "a.col2", "b1", "b2" });

        for (A a : generateData()) {
            for (B b : a.getbList()) {
                writer.write(b);
            }
        }
        writer.flush();
        System.out.println(out.toString());
    }

    private List<A> generateData() {
        List<A> data = new ArrayList<A>();

        for (int i = 0; i < 3; i++) {
            A a = new A();
            a.setCol1("col1 for a" + i);
            a.setCol2("col2 for a" + i);

            B firstB = new B();
            firstB.setB1("first b1 for a" + i);
            firstB.setB2("first b2 for a" + i);
            firstB.setA(a);

            B secondB = new B();
            secondB.setB1("second b1 for a" + i);
            secondB.setB2("second b2 for a" + i);
            secondB.setA(a);

            a.setbList(Arrays.asList(firstB, secondB));
            data.add(a);
        }

        return data;
    }

}

打印：

col1 for a0,col2 for a0,first b1 for a0,first b2 for a0
col1 for a0,col2 for a0,second b1 for a0,second b2 for a0
col1 for a1,col2 for a1,first b1 for a1,first b2 for a1
col1 for a1,col2 for a1,second b1 for a1,second b2 for a1
col1 for a2,col2 for a2,first b1 for a2,first b2 for a2
col1 for a2,col2 for a2,second b1 for a2,second b2 for a2

更新以发表评论

如果你不能添加关系，那么你可以使用CellProcessors（你甚至不需要使用Dozer）。我刚刚创建了3个简单的单元处理器：

ElementAt - 只需抓住所需索引的元素
GetB1 - 获取b1

B

GetB2 - 获取b2

B

在这里他们正在行动：

@Test
public final void test2() throws IOException {
    StringWriter out = new StringWriter();
    ICsvDozerBeanWriter writer = new CsvDozerBeanWriter(out, 
        CsvPreference.STANDARD_PREFERENCE);
    writer.configureBeanMapping(A.class, 
        new String[] { "col1", "col2", "bList", "bList" });

    for (A a : generateData()) {
        for (int i = 0; i < a.getbList().size(); i++) {
            CellProcessor[] processors = new CellProcessor[] { null, null, 
                new ElementAt(i, new GetB1()),
                new ElementAt(i, new GetB2()) };
            writer.write(a, processors);
        }
    }
    writer.flush();
    System.out.println(out.toString());
}

class GetB1 extends CellProcessorAdaptor {
    public Object execute(Object value, CsvContext context) {
        validateInputNotNull(value, context);
        return ((B) value).getB1();
    }
}

class GetB2 extends CellProcessorAdaptor {
    public Object execute(Object value, CsvContext context) {
        validateInputNotNull(value, context);
        return ((B) value).getB2();
    }
}

class ElementAt extends CellProcessorAdaptor {

    private final int index;

    public ElementAt(int index) {
        this.index = index;
    }

    public ElementAt(int index, CellProcessor next) {
        super(next);
        this.index = index;
    }

    public Object execute(Object value, CsvContext context) {
        validateInputNotNull(value, context);
        Object element = ((List<?>) value).get(index);
        return next.execute(element, context);
    }

}

输出：

col1 for a0,col2 for a0,first b1 for a0,first b2 for a0
col1 for a0,col2 for a0,second b1 for a0,second b2 for a0
col1 for a1,col2 for a1,first b1 for a1,first b2 for a1
col1 for a1,col2 for a1,second b1 for a1,second b2 for a1
col1 for a2,col2 for a2,first b1 for a2,first b2 for a2
col1 for a2,col2 for a2,second b1 for a2,second b2 for a2

P.S。除非你真的需要，否则我不建议提供你自己的推土机映射XML。（在这种情况下似乎没有必要）。

SuperCSV，Dozer：写入csv文件。对于具有多行列表的Object

1 个答案: