jdbc--取大量數據

最近使用jdbc方式查詢數據，保存爲csv文件中。固然你能夠在pl/sql中直接查出來，copy to excel就行了。但我想經過程序實現

 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;// 建立一個數據庫鏈接
10         PreparedStatement pre = null;// 建立預編譯語句對象，通常都是用這個而不用Statement
11         PreparedStatement pre2 = null;
12         ResultSet result = null;// 建立一個結果集對象
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\\貸後還款計劃_"+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);// 獲取鏈接
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 ";// 預編譯語句，「？」表明參數*/
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("數據庫鏈接已關閉！");
85             }
86             catch (Exception e)
87             {
88                 e.printStackTrace();
89             }
90         }
91     }

先讀取全部編號造成List，後遍歷這個List，先查出id再查詳細數據。這樣的數據csv文件中大約8萬多條

一條條的來確定慢，若是不按照編號，直接一次查出，數據是9萬多條。速度都很慢！！！

後來想提升下，至少要有個明顯的提高呀。寫文件這塊基本排除了，剩下的疑問就是ResultSet是否拿到了全部結果呢？

根據網上查到的資料和實際調試，得出答案：ResultSet默認一次取10條數據，怪不得要慢，若是一次所有讀入內存再寫入文件就必定很快了。

怎樣一次讀取全部數據呢？

sql改成讀取所有

 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";

 

設置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，

後來發現ResultSet也有個setFetchSize 方法，也是可行的，只是這個時候resultset中已經有了10條記錄直到循環10次後，再次使用result.next()纔去取100000，fetchSize才起做用

這樣設置後速度飛快！！！