package com.hy;

import java.io.FileOutputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import org.apache.log4j.Logger;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;

class Field{
    String name;    // 列名
    int size;        // 列容量
    String type;    // 列数据类型
    boolean allowNull;// 列是否允許为空
}

/**
 * 从数据库表中抽取字段信息存成Excel文件
 * @author horn1
 *
 */
public class XlsMaker {
    private static Logger log = Logger.getLogger(XlsMaker.class);

    // 连接到数据库的四大属性
    private static final String DRIVER = "com.mysql.jdbc.Driver";
    private static final String DBURL = "jdbc:mysql://192.168.161.130:3306/test?useUnicode=true&characterEncoding=utf-8";
    private static final String USER = "root";
    private static final String PSWD = "12345678";

    /**
     * 从表数组里取出表，从表里取出字段信息，每个表做成一个xls文件
     *
     * @param tables
     */
    public void makeXlsFrom(String[] tables) {
        final String exportPath="d:\\";
        Connection conn = null;
        Statement stmt = null;

        try {
            Class.forName(DRIVER).newInstance();
            conn = DriverManager.getConnection(DBURL, USER, PSWD);
            stmt = conn.createStatement();

            for(String table:tables) {
                List<Field> fields=fetchTableFields(conn,stmt,table,true);
                String xlsFilename=exportPath+table+getTimestamp()+".xls";

                writeFile(table,fields,xlsFilename);
            }
        } catch (Exception e) {
            System.out.print(e.getMessage());
        } finally {
            try {
                stmt.close();
                conn.close();
            } catch (SQLException e) {
                System.out.print("Can't close stmt/conn because of " + e.getMessage());
            }
        }
    }

    /**
     * 将表，字段信息写入文件xlsFilename
     * @param table
     * @param fields
     * @param xlsFilename
     * @throws Exception
     */
    private void writeFile(String table,List<Field> fields,String xlsFilename) throws Exception{
        // 得到四行
        List<String> allownulls=new ArrayList<String>();
        List<String> types=new ArrayList<String>();
        List<String> sizes=new ArrayList<String>();
        List<String> names=new ArrayList<String>();

        for(Field f:fields) {
            allownulls.add(String.valueOf(f.allowNull));
            types.add(f.type);
            sizes.add(String.valueOf(f.size));
            names.add(f.name);
        }

        HSSFWorkbook hssfWorkbook = new HSSFWorkbook();// 创建工作簿
        HSSFSheet sheet = hssfWorkbook.createSheet();// 新建Sheet
        hssfWorkbook.setSheetName(0, table);// 设置sheet名

        HSSFRow row = sheet.createRow(0);// 新建一行
        row.createCell(0).setCellValue("Allow null:");// 首个单元格写类型
        for(int i=0;i<allownulls.size();i++) {
            row.createCell(i+1).setCellValue(allownulls.get(i));// 其它写字段信息
        }

        row = sheet.createRow(1);
        row.createCell(0).setCellValue("Type:");
        for(int i=0;i<types.size();i++) {
            row.createCell(i+1).setCellValue(types.get(i));
        }

        row = sheet.createRow(2);
        row.createCell(0).setCellValue("Size:");
        for(int i=0;i<sizes.size();i++) {
            row.createCell(i+1).setCellValue(sizes.get(i));
        }

        row = sheet.createRow(3);
        row.createCell(0).setCellValue("Name:");
        for(int i=0;i<names.size();i++) {
            row.createCell(i+1).setCellValue(names.get(i));
        }

        // 将工作簿写入文件
        FileOutputStream fileOut = new FileOutputStream(xlsFilename);
        hssfWorkbook.write(fileOut);
        hssfWorkbook.close();

        log.info("文件 '"+xlsFilename+"' 写入完了.");
    }

    /**
     * 从表中取字段信息
     * @param conn
     * @param stmt
     * @param table
     * @param isFetchall:此参数为真时取所有字段，为假时取非空字段
     * @return
     * @throws Exception
     */
    private List<Field> fetchTableFields(Connection conn,Statement stmt,String table,boolean isFetchall)  throws Exception{
        List<Field> fields=new ArrayList<Field>();

        String sql = "select * from "+table+"";

        ResultSet rs = stmt.executeQuery(sql);
        ResultSetMetaData rsMetadata = rs.getMetaData();

        int count = rsMetadata.getColumnCount();
        for (int i=0; i<count; i++) {
            int index=i+1;

            String columnName = rsMetadata.getColumnLabel(index);// 列名
            int size =rsMetadata.getColumnDisplaySize(index);// 列容量
            String columnType = rsMetadata.getColumnTypeName(index);// 列数据类型
            boolean allowNull=(rsMetadata.isNullable(index)!=0);// 列是否允許为空

            Field f=new Field();
            f.name=columnName;
            f.size=size;
            f.type=columnType;
            f.allowNull=allowNull;

            if(isFetchall==true) {
                fields.add(f);
            }else {
                if(f.allowNull==false) {
                    fields.add(f);
                }
            }
        }

        rs.close();

        return fields;
    }

    /**
     * 取得当前时间戳
     * @return
     */
    private static String getTimestamp() {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmss");
        return sdf.format(new Date().getTime());
    }

    /**
     * 执行点
     * @param args
     */
    public static void main(String[] args) {
        String[] tables= {"emp","person","testdb"};
        XlsMaker xm=new XlsMaker();
        xm.makeXlsFrom(tables);
    }
}

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
      <modelVersion>4.0.0</modelVersion>
      <groupId>com.hy</groupId>
      <artifactId>FindNotnullColumns</artifactId>
      <version>0.0.1-SNAPSHOT</version>

      <dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.38</version>
        </dependency>

        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>

        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>poi</artifactId>
            <version>3.17</version>
        </dependency>
    </dependencies>
</project>