JDBC流ASCII和二進制數據

PreparedStatement對象可以使用輸入和輸出流來提供參數數據。能夠將整個文件放入可以容納大值的數據庫列，例如CLOB和BLOB數據類型。

有以下方法可用於流式傳輸數據 -

setAsciiStream()：此方法用於提供大的ASCII值。
setCharacterStream()：此方法用於提供較大的UNICODE值。
setBinaryStream()：此方法用於提供較大的二進制值。

setXXXStream()方法除了參數佔位符之外還需要額外的參數和文件大小。此參數通知驅動程序使用流向數據庫發送多少數據。

實例

考慮要將XML文件xml_data.xml上傳到數據庫表中。下面是XML文件的內容 -

<?xml version="1.0"?>
<Employee>
    <id>125</id>
    <first>Max</first>
    <last>Su</last>
    <Salary>18000</Salary>
    <Dob>18-08-1978</Dob>
<Employee>

將此XML文件保存在要運行此示例的同一目錄中。

此示例將在數據庫創建一個表：xml_data，然後將文件xml_data.xml上傳到此表中。

複製以下示例代碼，並保存在文件：StreamingData.java 中，編譯並運行如下 -

// Import required packages
import java.sql.*;
import java.io.*;
import java.util.*;

public class StreamingData {
   // JDBC driver name and database URL
   static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";  
   static final String DB_URL = "jdbc:mysql://localhost/EMP";

   //  Database credentials
   static final String USER = "root";
   static final String PASS = "123456";

   public static void main(String[] args) {
   Connection conn = null;
   PreparedStatement pstmt = null;
   Statement stmt = null;
   ResultSet rs = null;
   try{
      // Register JDBC driver
      Class.forName("com.mysql.jdbc.Driver");

      // Open a connection
      System.out.println("Connecting to database...");
      conn = DriverManager.getConnection(DB_URL,USER,PASS);

      //Create a Statement object and build table
      stmt = conn.createStatement();
      createXMLTable(stmt);

      //Open a FileInputStream
      File f = new File("xml_data.xml");
      long fileLength = f.length();
      FileInputStream fis = new FileInputStream(f);

      //Create PreparedStatement and stream data
      String SQL = "INSERT INTO XML_Data VALUES (?,?)";
      pstmt = conn.prepareStatement(SQL);
      pstmt.setInt(1,125);
      pstmt.setAsciiStream(2,fis,(int)fileLength);
      pstmt.execute();

      //Close input stream
      fis.close();

      // Do a query to get the row
      SQL = "SELECT Data FROM XML_Data WHERE id=125";
      rs = stmt.executeQuery (SQL);
      // Get the first row
      if (rs.next ()){
         //Retrieve data from input stream
         InputStream xmlInputStream = rs.getAsciiStream (1);
         int c;
         ByteArrayOutputStream bos = new ByteArrayOutputStream();
         while (( c = xmlInputStream.read ()) != -1)
            bos.write(c);
         //Print results
         System.out.println(bos.toString());
      }
      // Clean-up environment
      rs.close();
      stmt.close();
      pstmt.close();
      conn.close();
   }catch(SQLException se){
      //Handle errors for JDBC
      se.printStackTrace();
   }catch(Exception e){
      //Handle errors for Class.forName
      e.printStackTrace();
   }finally{
      //finally block used to close resources
      try{
         if(stmt!=null)
            stmt.close();
      }catch(SQLException se2){
      }// nothing we can do
      try{
         if(pstmt!=null)
            pstmt.close();
      }catch(SQLException se2){
      }// nothing we can do
      try{
         if(conn!=null)
            conn.close();
      }catch(SQLException se){
         se.printStackTrace();
      }//end finally try
   }//end try
   System.out.println("Goodbye!");
}//end main

public static void createXMLTable(Statement stmt) 
   throws SQLException{
   System.out.println("Creating XML_Data table..." );
   //Create SQL Statement
   String streamingDataSql = "CREATE TABLE XML_Data " +
                             "(id INTEGER, Data LONG)";
   //Drop table first if it exists.
   try{
      stmt.executeUpdate("DROP TABLE XML_Data");
   }catch(SQLException se){
   }// do nothing
   //Build table.
   stmt.executeUpdate(streamingDataSql);
}//end createXMLTable
}//end JDBCExample

編譯上面代碼，如下 -

F:\worksp\jdbc>javac -Djava.ext.dirs=F:\worksp\jdbc\libs StreamingData.java

執行上面編譯後的代碼，得到以下結果 -

F:\worksp\jdbc>java -Djava.ext.dirs=F:\worksp\jdbc\libs StreamingData
Connecting to database...
Thu Jun 01 21:42:00 CST 2017 WARN: Establishing SSL connection without server's identity verification is not recommended. According to MySQL 5.5.45+, 5.6.26+ and 5.7.6+ requirements SSL connection must be established by default if explicit option isn't set. For compliance with existing applications not using SSL the verifyServerCertificate property is set to 'false'. You need either to explicitly disable SSL by setting useSSL=false, or set useSSL=true and provide truststore for server certificate verification.
Creating XML_Data table...
<?xml version="1.0"?>
<Employee>
        <id>125</id>
        <first>Max</first>
        <last>Su</last>
        <Salary>18000</Salary>
        <Dob>18-08-1978</Dob>
<Employee>
Goodbye!

F:\worksp\jdbc>

在執行上面語句後，將在數據庫：emp下創建一個名稱爲：xml_data的表，現在查詢xml_data表中的數據，如下所示 -

mysql> select * from xml_data;
+-----+-----------------------------------------------------------------------------------------------------------------------------------+
| id  | Data                                                                                                                              |
+-----+-----------------------------------------------------------------------------------------------------------------------------------+
| 125 | <?xml version="1.0"?>
<Employee>
    <id>125</id>
    <first>Max</first>
    <last>Su</last>
    <Salary>18000</Salary>
    <Dob>18-08-1978</Dob>
<Employee> |
+-----+-----------------------------------------------------------------------------------------------------------------------------------+
1 row in set

mysql>

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應用示例

JDBC流ASCII和二進制數據

實例