JDBC备忘录6_处理大段文本和二进制数据
public static void create() throws Exception {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JdbcUtils.getConnection();String sql = "insert into clob_test(big_text) values (?) ";ps = conn.prepareStatement(sql);File file = new File("src/cn/itcast/jdbc/JdbcUtils.java");Reader reader = new BufferedReader(new FileReader(file));ps.setCharacterStream(1, reader, file.length());int i = ps.executeUpdate();System.out.println("i=" + i);reader.close();} finally {JdbcUtils.free(rs, ps, conn);}}
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它的主要原理是通过IO的Reader，将文件内容读到字符流中，然后写入到数据库中(File-->Reader-->DB)。
对于内存而言，把文件的内容载入内存，文件-->内容，需要读取的字符流Reader。
由于java 的String类型是没有限制的，
所以可以通过把Reader转化成String，然后通过 ps.setString(1, str)的形式插入数据库;
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读取clob类型的时候，先获取Reader，然后在写到其他地方。
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public static void read() throws Exception {Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {conn = JdbcUtils.getConnection();String sql = "select big_text from clob_test where id = ? ";ps = conn.prepareStatement(sql);ps.setInt(1, 1);rs = ps.executeQuery();while (rs.next()) {File file = new File("clob.txt");Clob clob = rs.getClob("big_text");Reader reader = clob.getCharacterStream();Writer writer = new BufferedWriter(new FileWriter(file));char[] buffer = new char[1024];//这里为什么要定义hasReader呢//因为在最后一次读取的时候不一定可以可以读到1024个数据//所以这里应该使用读取多少就写入多少int hasRead = 0;while ( (hasRead = reader.read(buffer)) > 0) {writer.write(buffer, 0, hasRead);}reader.close();writer.close();}} finally {JdbcUtils.free(rs, ps, conn);}}?
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大的二进制文本字段，在mysql中叫Blob
blob类型存放的数据小，无法存储时候可以使用longblob
blob类型的处理和大段文本数据处理的方式是一致的，都是借助IO来进行处理。
blob类型处理二进制文本信息，只能通过流处理，而不能通过字符来处理。
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public class BlobTest {public static void main(String[] args) throws SQLException, IOException {//writeBlob();readBlob();}public static void readBlob() throws SQLException, IOException {String sql = "select big_blob from blob_test where id = ? ";Connection conn = JdbcUtils.getConnection();PreparedStatement pstmt = conn.prepareStatement(sql);pstmt.setInt(1, 2);ResultSet rs = pstmt.executeQuery();while (rs.next()) {Blob blob = rs.getBlob("big_blob");InputStream is = blob.getBinaryStream();File file = new File("a.jpg");OutputStream os = new BufferedOutputStream(new FileOutputStream(file));byte[] buffer = new byte[1024];int hasRead = 0;while ((hasRead = is.read(buffer)) > 0) {os.write(buffer, 0, hasRead);}is.close();os.close();}JdbcUtils.free(rs, pstmt, conn);}public static void writeBlob() throws SQLException, IOException {String sql = "insert into blob_test(big_blob) values(?) ";Connection conn = JdbcUtils.getConnection();PreparedStatement pstmt = conn.prepareStatement(sql);File file = new File("bg.jpg");InputStream is = new BufferedInputStream(new FileInputStream(file));pstmt.setBlob(1, is, file.length());boolean flag = pstmt.execute();System.out.println("flag = " + flag);is.close();JdbcUtils.free(null, pstmt, conn);}}?