jdbc--取大量数据

最近使用jdbc方式查询数据，保存为csv文件中。当然你可以在pl/sql中直接查出来，copy to excel就好了。但我想通过程序实现

 1 @Test
 2     public void test() throws IOException {
 3         BufferedReader reader=new BufferedReader(new InputStreamReader(new FileInputStream("C:\\Users\\yhzh\\Desktop\\zh_20160913")));
 4         String tmp=null;
 5         List<String> nos=new ArrayList<String>();
 6         while((tmp=reader.readLine()) !=null)
 7             nos.add(tmp);
 8
 9         Connection con = null;// 创建一个数据库连接
10         PreparedStatement pre = null;// 创建预编译语句对象，一般都是用这个而不用Statement
11         PreparedStatement pre2 = null;
12         ResultSet result = null;// 创建一个结果集对象
13         BufferedWriter csvWriter=null;
14         try
15         {
16             String tag=(new SimpleDateFormat("hhmmss")).format(new Date());
17             csvWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("C:\\Users\\yhzh\\Desktop\\贷后还款计划_"+tag+".csv")), "utf-8"));
18
19             Class.forName("oracle.jdbc.driver.OracleDriver");
20             //:6006/hotfix
21             String url = "jdbc:oracle:thin:@//*.*.*.*:16030/zcgl",user = "*",password = "*";
22             con = DriverManager.getConnection(url, user, password);// 获取连接
23             String sql="select max(lr_id) from t_loan_request where LR_REQUESTSTATUS =‘2‘ and lr_applyid=?";
24             /*String sql = 27                     "select req.LR_APPLYID,CURR_PERIODS,REPAY_DAY,\n" +
28                     "(NEEDREPAY_PRINCIPAL+NEEDREPAY_INTEREST+NEEDREPAY_ADMIFEE+nvl(RISK_AMOUNT,0)+nvl(SERVICEFEE,0)+nvl(PARKINGFEE,0))NEEDREPAY_TOTAL,\n" +
29                     "PERIOD_REPAY_AMOUNT \n" +
30                     "from(\n" +
31                     "  select lr_id,LR_APPLYID from t_loan_request t \n" +
32                     "  where t.LR_REQUESTSTATUS =‘2‘ and t.creater=‘PostLoanOuterAction‘\n" +
33                     "  order by lr_id desc)req\n" +
34                     "left join t_repay_plan rp\n" +
35                     "on req.lr_id=rp.lr_id\n" +
36                     "order by req.lr_id,CURR_PERIODS ";// 预编译语句，“？”代表参数*/
37             pre = con.prepareStatement(sql);
38             pre2=con.prepareStatement("select CURR_PERIODS,REPAY_DAY,\n" +
39                     "(NEEDREPAY_PRINCIPAL+NEEDREPAY_INTEREST+NEEDREPAY_ADMIFEE+nvl(RISK_AMOUNT,0)+nvl(SERVICEFEE,0)+nvl(PARKINGFEE,0))NEEDREPAY_TOTAL,\n" +
40                     "PERIOD_REPAY_AMOUNT \n" +
41                     "from t_repay_plan\n" +
42                     "where lr_id=? " +
43                     "order by CURR_PERIODS");
44             for(String no:nos){
45                 pre.setString(1,no);
46                 result = pre.executeQuery();
47                 if(result.next()) {
48                     long lrId=result.getLong(1);
49                     pre2.setLong(1,lrId);
50                     result = pre2.executeQuery();
51                     while (result.next()) {
52                         csvWriter.write(no);
53                         csvWriter.write(",");
54                         csvWriter.write(result.getString(1));
55                         csvWriter.write(",");
56                         csvWriter.write(result.getString(2));
57                         csvWriter.write(",");
58                         csvWriter.write(result.getString(3));
59                         csvWriter.write(",");
60                         csvWriter.write(result.getString(4));
61                         csvWriter.newLine();
62                     }
63                 }
64             }
65
66             csvWriter.flush();
67         }
68         catch (Exception e)
69         {
70             e.printStackTrace();
71         }
72         finally
73         {
74             try
75             {
76                 if(csvWriter !=null)
77                     csvWriter.close();
78                 if (result != null)
79                     result.close();
80                 if (pre != null)
81                     pre.close();
82                 if (con != null)
83                     con.close();
84                 System.out.println("数据库连接已关闭！");
85             }
86             catch (Exception e)
87             {
88                 e.printStackTrace();
89             }
90         }
91     }

先读取所有编号形成List，后遍历这个List，先查出id再查详细数据。这样的数据csv文件中大约8万多条

一条条的来肯定慢，如果不按照编号，直接一次查出，数据是9万多条。速度都很慢！！！

后来想提高下，至少要有个明显的提升呀。写文件这块基本排除了，剩下的疑问就是ResultSet是否拿到了所有结果呢？

根据网上查到的资料和实际调试，得出答案：ResultSet默认一次取10条数据，怪不得要慢，如果一次全部读入内存再写入文件就一定很快了。

怎样一次读取所有数据呢？

sql改为读取全部

 1 String sql="select req.LR_APPLYID,CURR_PERIODS,REPAY_DAY,\n" +
 2     "(NEEDREPAY_PRINCIPAL+NEEDREPAY_INTEREST+NEEDREPAY_ADMIFEE+nvl(RISK_AMOUNT,0)+nvl(SERVICEFEE,0)+nvl(PARKINGFEE,0))NEEDREPAY_TOTAL,\n" +
 3     "PERIOD_REPAY_AMOUNT \n" +
 4     "from(\n" +
 5     "  select lr_id,LR_APPLYID from t_loan_request t \n" +
 6     "  where t.LR_REQUESTSTATUS =‘2‘ and t.creater=‘PostLoanOuterAction‘\n" +
 7     "  order by lr_id desc)req\n" +
 8     "left join t_repay_plan rp\n" +
 9     "on req.lr_id=rp.lr_id\n" +
10     "order by req.lr_id,CURR_PERIODS";

设置PreparedStatement：

1 pre = con.prepareStatement(sql);
2 pre.setFetchSize(100000);
3 result = pre.executeQuery();
4 //result.setFetchSize(100000);

主要是PreparedStatement的 setFetchSize 方法，

后来发现ResultSet也有个setFetchSize 方法，也是可行的，只是这个时候resultset中已经有了10条记录直到循环10次后，再次使用result.next()才去取100000，fetchSize才起作用

这样设置后速度飞快！！！