「java创建clob」java创建class后首行报错
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java clob
java clob是什么，让我们一起了解一下？
CLOB是内置类型，将字符大对象存储为数据库表某一行中的一个列值。默认情况下，驱动程序使用SQL locator实现Clob对象，这意味着CLOB对象包含一个指向SQL CLOB数据的逻辑指针而不是数据本身。
在JAVA如何使用CLOB进行操作？
在绝大多数情况下，有2种方法使用CLOB。
1、相对比较小的，可以用String进行直接操作，把CLOB看成字符串类型即可。
2、如果比较大，可以用 getAsciiStream 或者 getUnicodeStream 以及对应的 setAsciiStream 和 setUnicodeStream 即可。
（1）读取数据：
ResultSet rs = stmt.executeQuery("SELECT TOP 1 * FROM Test1"); rs.next(); Reader reader = rs.getCharacterStream(2);
（2）插入数据：
PreparedStatement pstmt = con.prepareStatement("INSERT INTO test1 (c1_id, c2_vcmax) VALUES (?, ?)"); pstmt.setInt(1, 1); pstmt.setString(2, htmlStr); pstmt.executeUpdate();
（3）更新数据：
Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("SELECT * FROM test1"); rs.next(); Clob clob = rs.getClob(2); long pos = clob.position("dog", 1); clob.setString(1, "cat", len, 3); rs.updateClob(2, clob); rs.updateRow();
那么java是如何操作数据库clob字段的？
示例代码如下： package com.test.db.clob; import java.io.BufferedReader; import java.io.IOException; import java.io.Writer; import java.sql.Clob; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class ClobTest {undefined private static Connection conn; static {undefined try {undefined Class.forName("oracle.jdbc.driver.OracleDriver"); conn = DriverManager.getConnection( "jdbc:oracle:thin:@localhost:1521:orcl","scott","tiger"); } catch (ClassNotFoundException e) {undefined e.printStackTrace(); } catch (SQLException e) {undefined e.printStackTrace(); } } public static void main(String[] args) throws SQLException, IOException {undefined testInsert(); testUpdate(); testRead(); } private static void testInsert() throws SQLException {undefined String sql = "insert into test_clob values(1, empty_clob())"; Statement stm = conn.createStatement(); stm.execute(sql); } private static void testUpdate() throws SQLException, IOException {undefined String sql = "select content from test_clob where id = 1 for update"; Statement stm = conn.createStatement(); ResultSet rs = stm.executeQuery(sql); while (rs.next()) {undefined Clob c = rs.getClob(1); c.truncate(0);// clear Writer w = c.setCharacterStream(1);//The first position is 1 w.write("abc"); w.close(); c.setString(c.length() + 1, "abc"); conn.commit(); } } private static void testRead() throws SQLException, IOException {undefined String sql = "select content from test_clob where id = 1"; PreparedStatement pstm = conn.prepareStatement(sql); ResultSet rs = pstm.executeQuery(); while (rs.next()) {undefined Clob clob = rs.getClob("content"); System.out.println("clob.getSubString(1, 2) -- " + clob.getSubString(1, 2)); System.out.println("clob.getSubString(1, (int)clob.length()) -- " + clob.getSubString(1, (int)clob.length())); BufferedReader r = new BufferedReader(clob.getCharacterStream()); String s; while ((s = r.readLine()) != null) {undefined System.out.println(s); } r.close(); } } }
java往数据库存储大文件
你好。请问什么数据库。oracle如下
数据库中提供了两种字段类型 Blob 和 Clob 用于存储大型字符串或二进制数据（如图片）。
Blob 采用单字节存储，适合保存二进制数据，如图片文件。
Clob 采用多字节存储，适合保存大型文本数据。
首先创建一个空 Blob/Clob 字段，再从这个空 Blob/Clob字段获取游标，例如下面的代码：
PreparedStatement ps = conn.prepareStatement( " insert into PICTURE(image,resume) values(?,?) " );
// 通过oralce.sql.BLOB/CLOB.empty_lob()构造空Blob/Clob对象
ps.setBlob( 1 ,oracle.sql.BLOB.empty_lob());
ps.setClob( 2 ,oracle.sql.CLOB.empty_lob());
ps.excuteUpdate();
ps.close();
// 再次对读出Blob/Clob句柄
ps = conn.prepareStatement( " select image,resume from PICTURE where id=? for update " );
ps.setInt( 1 , 100 );
ResultSet rs = ps.executeQuery();
rs.next();
oracle.sql.BLOB imgBlob = (oracle.sql.BLOB)rs.getBlob( 1 );
oracle.sql.CLOB resClob = (oracle.sql.CLOB)rs.getClob( 2 );
// 将二进制数据写入Blob
FileInputStream inStream = new FileInputStream( " c://image.jpg " );
OutputStream outStream = imgBlob.getBinaryOutputStream();
byte [] buf = new byte [ 10240 ];
int len;
while (len = inStream.read(buf) 0 ) {
outStream.write(buf, 0 ,len);
}
inStream.close();
outStream.cloese();
// 将字符串写入Clob
resClob.putString( 1 , " this is a clob " );
// 再将Blob/Clob字段更新到数据库
ps = conn.prepareStatement( " update PICTURE set image=? and resume=? where id=? " );
ps.setBlob( 1 ,imgBlob);
ps.setClob( 2 ,resClob);
ps.setInt( 3 , 100 );
ps.executeUpdate();
ps.close();
java怎样创建一个blob对象
java向oracle写入blob
public void doWriteInHis(String id, String XML) {
int flag = 0;
Connection conn = null;
PreparedStatement pstmt = null;
ResultSet rest = null;
StringBuffer insql = new StringBuffer();
insql.append("insert into test (id,IN_XML) ");
insql.append("values(?,empty_clob()) ");
StringBuffer sqlSelect = new StringBuffer();
sqlSelect.append("SELECT IN_XML FROM test ");
sqlSelect.append(" WHERE id = ? for update");
try {
conn = getConnection();
pstmt = conn.prepareStatement(insql.toString());
int index = 1;
pstmt.setString(index++, id);
flag = pstmt.executeUpdate();
pstmt.close();
if (flag 0) {
pstmt = conn.prepareStatement(sqlSelect.toString());
index = 1;
pstmt.setString(index++, seq);
conn.setAutoCommit(false);
rest = pstmt.executeQuery();
if (rest.next()) {
oracle.sql.CLOB clob = (oracle.sql.CLOB) rest.getClob(1);
Writer os = clob.getCharacterOutputStream();
os.write(XML);
os.flush();
os.close();
}
conn.commit();
conn.setAutoCommit(true);
}
} catch (Exception e) {
SysLog.writeLogs("WriteHisDAOImpl", GlobalParameters.ERROR,
"WriteHisDAOImpl--doWriteInHis()-2:" + e.getMessage());
} finally {
close(conn);
}
}
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