JDBC流ASCII和二進製數據
PreparedStatement對象必須使用輸入和輸出流提供參數數據的能力。這使能夠將整個文件到數據庫列,可容納較大的值,如CLOB和BLOB數據類型。
有下列方法,可用於將數據傳送:
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setAsciiStream(): 這個方法是用來提供大的ASCII值。
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setCharacterStream(): 這個方法是用來提供大的UNICODE值。
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setBinaryStream(): 這個方法是用來提供大的二進製值。
setXXXStream()方法需要一個額外的參數,文件大小,除了參數占位符。這個參數通知驅動有多少數據要使用的流被發送到數據庫中。
例子
考慮到要上傳一個XML文件XML_Data.xml到數據庫表。下麵是這個XML文件的內容:
<?xml version="1.0"?> <Employee> <id>100</id> <first>Zara</first> <last>Ali</last> <Salary>10000</Salary> <Dob>18-08-1978</Dob> <Employee>
保持這個XML文件在要運行這個例子相同的目錄。
這個例子將創建一個數據庫表XML_Data,然後提交XML_Data.xml將被上傳到該表中。
複製下麵的例子JDBCExample.java,編譯並運行,如下所示:
// Import required packages import java.sql.*; import java.io.*; import java.util.*; public class JDBCExample { // 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 = "username"; static final String PASS = "password"; 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(1,100); 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=100"; 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
現在讓我們來編譯上麵的例子如下:
C:>javac JDBCExample.java C:>
當運行JDBCExample,它會產生以下結果:
C:>java JDBCExample Connecting to database... Creating XML_Data table... <?xml version="1.0"?> <Employee> <id>100</id> <first>Zara</first> <last>Ali</last> <Salary>10000</Salary> <Dob>18-08-1978</Dob> <Employee> Goodbye! C:>