Android 通过java bean 将数据写入csv文件

前几天遇到了将csv文件导入到android应用中的需求，自己运用java反射技术实现了该功能，今天又遇到了将android SQLite数据库中的数据导出到csv文件中并同步到后台服务器中的需求。于是乎，基于上一篇文章Android 读取csv文件并转换为java bean，继续改造代码，让其支持Java Bean导出数据到csv文件中。废话不多说，直接上代码：

改造后的CsvField.java

import java.lang.annotation.*;

/**
 * @author [email protected]
 * Created by Administrator on 2019/9/23 0023.
 */
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface CsvField {
    /**
     * 要将某个java类字段持久化到csv文件里的表头字段名称
     * @return 表头字段名称
     */
    String name();

    /**
     * 是否将该java类属性持久化到文件内
     * @return 默认true，将属性持久化到文件内。false忽略该字段
     */
    boolean isWrite() default true;
}

CsvWriter.java

import java.io.*;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.*;

/**
 * @author [email protected]
 * Created by Administrator on 2019/9/26 1323.
 */
public class CsvWriter {
    private static CsvWriter instance = null;

    private String SEPARATOR = ",";

    private String CHARSET = "UTF-8";

    public static CsvWriter getInstance(String separator, String charset) {
        instance = getInstance();
        instance.CHARSET = charset;
        instance.SEPARATOR = separator;
        return instance;
    }

    public static CsvWriter getInstance() {
        if (instance == null) {
            instance = new CsvWriter();
        }
        return instance;
    }

    private CsvWriter() {
    }

    /**
     * 存储csv文件的表头数据和Java Bean Field 的对应关系
     */
    private static Map<String, Field> map = new LinkedHashMap<>();

    private <T> void writeDataToFile(List<T> dataList, String targetFile) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException, IOException {
        // TODO: 2019/9/26 13:12  从集合中获取一个实例对象，根据对象使用反射技术获取所有的 Field
        T obj = dataList.get(0);
        Class<?> clazz = obj.getClass();
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
            CsvField csvField = field.getAnnotation(CsvField.class);
            if (csvField != null) {
                String name = csvField.name();
                boolean write = csvField.isWrite();
                if (write) {
                    map.put(name, field);
                }
            }
        }

        Set<String> csvFieldNames = map.keySet();
        List<String> tmp;
        OutputStream output;
        output = new FileOutputStream(new File(targetFile));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(output, CHARSET));
        bw.write(String.join(SEPARATOR, csvFieldNames));
        bw.newLine();
        for (T o : dataList) {
            tmp = new ArrayList<>();
            for (String csvFieldName : csvFieldNames) {
                Field field = map.get(csvFieldName);
                String fieldName = field.getName();
                String firstUpperCase = getFirstUpperCase(fieldName);
                Method method = clazz.getMethod("get" + firstUpperCase);
                Object invoke = method.invoke(o);
                String value = String.valueOf(invoke);
                tmp.add(value);
            }
            String join = String.join(SEPARATOR, tmp);
            bw.write(join);
            bw.newLine();
        }
        bw.flush();
        bw.close();
    }

    /**
     * 字符串首字母转大写
     *
     * @param fieldName 字段名称
     * @return 首字母大写的字段名称
     */
    private static String getFirstUpperCase(String fieldName) {
        char[] chars = fieldName.toCharArray();
        String s = String.valueOf(chars[0]).toUpperCase();
        chars[0] = s.toCharArray()[0];
        return new String(chars);
    }

    public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, IOException {

        List<Oil> list = new ArrayList<>();
        list.add(new Oil(1, "001", "A油"));
        list.add(new Oil(2, "002", "B油"));
        CsvWriter.getInstance("^", "UTF-8")
                .writeDataToFile(list, "E:\\data\\output.csv");
    }
}

Oil.java

import java.io.Serializable;
/**
 * @author [email protected]
 * Created by Administrator on 2019/9/26 0023.
 */
public class Oil implements Serializable {


    public Oil(Integer id, String oilCode, String oilName) {
        this.id = id;
        this.oilCode = oilCode;
        this.oilName = oilName;
    }

    @CsvField(name = "id")
    private Integer id;

    @CsvField(name = "oil_code",isWrite = false)
    private String oilCode;

    @CsvField(name = "oil_name")
    private String oilName;

    public String getOilCode() {
        return oilCode;
    }

    public void setOilCode(String oilCode) {
        this.oilCode = oilCode;
    }

    public String getOilName() {
        return oilName;
    }

    public void setOilName(String oilName) {
        this.oilName = oilName;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }
}