查询多个关联表的数据输出到Excel

举个小栗子：

查询student表中的数据，并且通过students中的关联字段cid查询classtable中的信息。

步骤一：可以选择建立一个连接池。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.LinkedList;



public class MyPool {
    private String url = "jdbc:sqlserver://120.78.80.233;databasename=ZBJF_Product_Test1";
    //"useSSL=false"字段可防止不必要的报错
    private String user = "zbjf";
    private String password = "zbjf1234!@#$";
    //数据库的用户名与密码
    private static String driverClass="com.microsoft.sqlserver.jdbc.SQLServerDriver";

    private int initSize = 5;//初始连接数量
    private int maxSize = 20;//池中连接数上线
    private LinkedList<Connection> conList = new LinkedList<Connection>();
    private int currentsize = 0;
    static {
        try {
            Class.forName(driverClass);
        }catch(ClassNotFoundException e){
            e.printStackTrace();
        }
    }
    //获取连接
    private Connection getConnection(){
        Connection conn=null;
        try{
            conn=(Connection)DriverManager.getConnection(url,user,password);
        }catch(SQLException e){
            e.printStackTrace();
        }
        return conn;
    }
    //初始化池
    public MyPool(){
        for(int i=0;i<initSize;i++){
            Connection connection = this.getConnection();
            conList.add(connection);
            currentsize++;
        }
    }
    //用户只能从池中获取连接
    public Connection getConnFromPool(){
        if(conList.size()>0){
            Connection connection =conList.getFirst();
            conList.removeFirst();
            return connection;
        }
        else if(conList.size()==0&¤tsize<maxSize){
            currentsize++;
            conList.addLast(this.getConnection());
            Connection connection=conList.getFirst();
            conList.removeFirst();
            return connection;
        }
        throw new RuntimeException("连接达到上限，请等待");
    }
    //用户释放链接到池
    public void releaseConnection(Connection connection){
        conList.addLast(connection);
    }
}

步骤二：进行输出操作

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;

import com.mysql.jdbc.Statement;


public class ImportExcelTest {

	 private static  MyPool pool=null;
	 private static Connection conn=null;
	 private static  Workbook book=null;
	 private static Statement st1=null;
	 private static Statement st2=null;
	 private static ResultSet rs1=null;
	 private static ResultSet rs2=null;
	 private static String sql1="select name,class,score,cid from students";
	 //private static String sql2="SELECT classname FROM classtable WHERE id=";
	 //创建一个List来存储多行数据，Map存储一行
	 private static List<Map<String,Object>> list=new ArrayList<Map<String,Object>>();
	 
	 public static void  importExecel() throws SQLException, FileNotFoundException, IOException {
		  pool=new MyPool();
		  conn=pool.getConnection();
		  //创建excel表
		  book=new HSSFWorkbook();
          String table_name="学生成绩统计表";
          //在当前excel创建一个子表  ss与sl区别
          Sheet sheet=(Sheet) book.createSheet(table_name);
           st1=(Statement) conn.createStatement();
           st2=(Statement) conn.createStatement();
		  
          rs1=st1.executeQuery(sql1);
		//创建行
          Row row1=(Row) sheet.createRow(0);
		//设置表头信息(写入excel左上角从(0,0)开始)
          String head[]= {"姓名","课程","得分","班级"};
          
		  for(int i=0;i<head.length;i++) {
			  //创建单元格
			  Cell cell=(Cell) row1.createCell(i);
			  //写入数据
			  cell.setCellValue(head[i]);
		  }
		  //设置表格信息
		  while(rs1.next()) {
			  //遍历将数据一行一行存入Map
			  Map<String ,Object> m=new HashMap<String,Object>();
			  for(int i=1;i<=rs1.getMetaData().getColumnCount();i++) {
				  if("name".equals(rs1.getMetaData().getColumnName(i))) {
					  m.put("name", rs1.getString(i));
				  }
				  if("class".equals(rs1.getMetaData().getColumnName(i))) {
					  m.put("class", rs1.getString(i));
				  }
				  if("score".equals(rs1.getMetaData().getColumnName(i))) {
					  System.out.println("score+"+rs1.getInt(i));
					  m.put("score", rs1.getInt(i));
				  }
				  if("cid".equals(rs1.getMetaData().getColumnName(i))) {
					  System.out.println("cid"+rs1.getInt(i));
					  String sql2="SELECT classname FROM classtable WHERE id="+rs1.getInt(i);
					  rs2=st2.executeQuery(sql2);
					  while(rs2.next()) {
						  for(int j=1;j<=rs2.getMetaData().getColumnCount();j++) {
								  m.put("classname", rs2.getString(j));
								  System.out.println("rs2"+rs2.getString(j));
						  }
					  }
				  }
			  }
			  for(int z=0;z<m.size();z++) {
				  System.out.println("class:"+m.get("class")+"score:"+m.get("score"));
			  }
			  int index=1;
			  list.add(m);
			  String [] header= {"name","class","score","classname"};
			  for(int i=0;i<list.size();i++) {
				  Row row=sheet.createRow(index++);
				  Map<String,Object> map2=list.get(i);
				  for(int j=0;j<header.length;j++) {
					  Cell cell=row.createCell(j);
					  cell.setCellValue(j);
					 cell.setCellValue(map2.get(header[j])+"");
				  }
			  }	
		  }
		  book.write(new FileOutputStream("D://aaa//"+table_name+System.currentTimeMillis()+".xls"));
        rs1.close();
        rs2.close();
        st1.close();
        st2.close();
        con.close();
	  }
	 
	
       public static void main(String[] args) throws FileNotFoundException, SQLException, IOException {
    	   importExecel();
    	   //close(rs1,rs2,st1,st2,conn);
    	   
	}
}