Question

我尝试使用Jackson CsvParser阅读简单的CSV文件。我已经按照教程，但我一直收到以下错误：

com.fasterxml.jackson.databind.RuntimeJsonMappingException: No suitable constructor found for type [simple type, class data.MyPojo$MyPojo]: can not instantiate from JSON object (missing default constructor or creator, or perhaps need to add/enable type information?)
at [Source: java.io.InputStreamReader@3d362683; line: 2, column: 1]
at com.fasterxml.jackson.databind.MappingIterator.next(MappingIterator.java:121)

CSV文件MYFILE.CSV非常简单：

FirstAddress,SecondAddress
Blah,Blah
Etc,Etc

代码也是如此：

public class MyPojoLookup {
    private final static String FILENAME = "/MYFILE.CSV";
    private final static CsvMapper mapper = new CsvMapper();

    static {
        CsvSchema schema = CsvSchema.emptySchema().withHeader();

        InputStream input = (MyPojoLookup.class.getResourceAsStream(FILENAME));

        MappingIterator<MyPojo> it;
        try {
            it = mapper.reader(MyPojo.class).with(schema).readValues(input);

            while (it.hasNext()){
                MyPojo row = it.next();
                log.info(row.toString());
            }
        } catch (Exception e) {
            log.error("Cannot load the addresses", e);
            System.exit(-1);
        }
    }

    private class MyPojo {
        public String address1;
        public String address2;

        public MyPojo(String address1, String address2) {
            super();
            this.address1 = address1;
            this.address2 = address2;
        }

        @Override
        public String toString() {
            return "MyPojo ["address1=" + address1 + ", address2=" + address2 + "]";
        }
    }
}

Answer 1

您的代码有三个问题：

1）您需要将要读取的属性传递给CSV架构，例如address1和address2：

CsvSchema schema = CsvSchema.builder()
                            .addColumn("address1")
                            .addColumn("address2")
                            .build();

2）你的内部类没有标记为静态，请检查this link，解释为什么这是必要的。

3）您缺少默认构造函数。

这是一个包含所有修复程序的完整列表：

import com.fasterxml.jackson.databind.MappingIterator;
import com.fasterxml.jackson.dataformat.csv.CsvMapper;
import com.fasterxml.jackson.dataformat.csv.CsvSchema;  
import java.io.InputStream;

public class MyPojoLookup {

    private final static String FILENAME = "/MYFILE.CSV";
    private final static CsvMapper mapper = new CsvMapper();

    public static void main(String[] args) {
        CsvSchema schema = CsvSchema.builder().addColumn("address1").addColumn("address2").build();

        InputStream input = (MyPojoLookup.class.getResourceAsStream(FILENAME));

        MappingIterator<MyPojo> it;
        try {
            it = mapper.reader(MyPojo.class).with(schema).readValues(input);

            while (it.hasNext()){
                MyPojo row = it.next();
                System.out.println(row.toString());
            }
        } catch (Exception e) {
            System.out.println("Cannot load the addresses");
            e.printStackTrace();
            System.exit(-1);
        }
    }

    private static class MyPojo {
        public String address1;
        public String address2;

        public MyPojo() {}

        public MyPojo(String address1, String address2) {
            super();
            this.address1 = address1;
            this.address2 = address2;
        }

        @Override
        public String toString() {
            return "MyPojo [address1=" + address1 + ", address2=" + address2 + "]";
        }
    }
}

CsvParser＆＃34;找不到类型＆＃34的合适构造函数;

1 个答案: