java对Blob读写

落日映苍穹つ 2022-08-10 14:41 211阅读 0赞

package com.you.sister;
    
    import java.io.BufferedInputStream;
    import java.io.BufferedOutputStream;
    import java.io.DataOutputStream;
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.FileOutputStream;
    import java.io.InputStream;
    import java.sql.Blob;
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.PreparedStatement;
    import java.sql.ResultSet;
    import java.util.Properties;
    
    public class BlobTest {
    
    	public static Connection conn;
    	
    	public static Connection getConn() throws Exception {
    		FileInputStream fis = new FileInputStream(new File("jdbc.properties"));
    		Properties prop = new Properties();
    		prop.load(fis);
    		String driver = prop.getProperty("jdbc.driver");
    		String url = prop.getProperty("jdbc.url");
    		String username = prop.getProperty("jdbc.username");
    		String password = prop.getProperty("jdbc.password");
    		Class.forName(driver);
    		return  DriverManager.getConnection(url, username, password);
    	}
    	
    	public static void main(String[] args) throws Exception {
    		conn = getConn();
    		readBlob();
    		writeBlob();
    		conn.close();
    	}
    	
    	/**
    	 * 从数据库中读大对象出来
    	 * 保存在本地
    	 */
    	public static void readBlob() {
    		try {
    			String readSql = "select * from emp where empno = ?";
    			PreparedStatement ps = conn.prepareStatement(readSql);
    			ps.setInt(1, 7369);
    			ResultSet rs = ps.executeQuery();
    			while (rs.next()) {
    				Blob image = rs.getBlob("image");
    				DataOutputStream dos = 
    					// 在FileOutputStream中指定文件输出路径
    					new DataOutputStream(new FileOutputStream(7369 + "_image.jpeg"));
    				InputStream fis = image.getBinaryStream();
    				int out;
    				byte[] outByte = new byte [100];
    				// 将blob对象输入流写入本地输出流中
    				while ((out = fis.read(outByte)) != -1) {
    					dos.write(outByte);
    				}
    				fis.close();
    				dos.flush();
    				dos.close();
    			}
    			rs.close();
    			ps.close();
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    	
    	/**
    	 * 将大对象文件保存进数据库中
    	 */
    	public static void writeBlob() {
    		try {
    			BufferedInputStream fis = 
    				new BufferedInputStream(new FileInputStream(new File("D:\\Tulips.jpg")));
    			// 如果是新插入字段，则将大对象对应字段插入为empty_clob();
    			// 如果是修改，则可以先update 该行数据，将大对象对应字段设置为empty_clob();
    			String writeSql = "select * from emp where empno = ? for update";
    			PreparedStatement ps = conn.prepareStatement(writeSql);
    			ps.setInt(1, 7499);
    			conn.setAutoCommit(false);
    			ResultSet rs = ps.executeQuery();
    			while (rs.next()) {
    				oracle.sql.BLOB image = (oracle.sql.BLOB)rs.getBlob("image");
    				BufferedOutputStream bos = new BufferedOutputStream(image.getBinaryOutputStream());
    				int c;
    				// 将实际文件中的内容以二进制的形式来输出到blob对象对应的输出流中
    				while ((c = fis.read()) != -1) {
    					bos.write(c);
    				}
    				fis.close();
    				bos.close();
    			}
    			conn.commit();
    			rs.close();
    			ps.close();
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    }

从数据库中读blob对象出来相对比较容易

从本地向数据库写blob对象相对难一些，主要注意两点：

**1  要处理的blob字段必须先设置为empt\_clob()**

**2  使用事务控制向数据库的写入操作**