一个简单的Blob存取例子

我会带着你远行 2024-02-17 20:06 14阅读 0赞

Code:

1.  import java.io.\*;
2.  import java.sql.\*;
3.  
4.  /\*\*
5.   \* 测试操作blob数据
6.   \*/
7.  public class BlobTest \{
8.  Connection con = null;
9.  private static String filepath = "d:/test/smile.jpg";
10. private static String fileoutpath = "d:/test/smilecopy.jpg";
11. /\*\*
12.  \* 往数据库中添加BLOB数据
13.  \*/
14. public void addBlob() \{
15. try \{
16. 
17. // 创建一个PreparedStatement实例
18. PreparedStatement pstmt = con
19. .prepareStatement("insert into blobtest values(1,?)");
20. File file = new File(filepath);
21. FileInputStream fis = new FileInputStream(file);
22. // 把输入流设置为预处理语句的对象。
23. pstmt.setBinaryStream(1, fis, (int) file.length());
24. // 执行更新
25. pstmt.executeUpdate();
26. pstmt.close();
27. fis.close();
28. 
29. \} catch (Exception e) \{
30. e.printStackTrace();
31. \}
32. \}
33. 
34. /\*\*
35.  \* 创建一个表
36.  \*/
37. public void createTable() \{
38. try \{
39. con.createStatement().execute(
40. "create table blobtest (id int ,pic blob,"
41. \+ "constraint pk\_blobtest primary key(id));");
42. \} catch (Exception e) \{
43. e.printStackTrace();
44. \}
45. \}
46. 
47. /\*\*
48.  \* 从数据库中读取BLOB数据
49.  \*/
50. public void getBlob() \{
51. 
52. try \{
53. // 创建一个Statement实例
54. Statement stmt = con.createStatement();
55. ResultSet rst = stmt
56. .executeQuery("select \* from blobtest where id=1");
57. rst.next();
58. // 获得blob数据和它的输入流，然后通过输入流把数据写到文件中。
59. Blob blob = rst.getBlob("pic");
60. FileOutputStream out = new FileOutputStream(new File(
61. fileoutpath));
62. InputStream in = blob.getBinaryStream();
63. int i;
64. while ((i = in.read()) != -1)
65. out.write(i);
66. // 关闭输入、输出流.
67. in.close();
68. out.close();
69. 
70. \} catch (Exception e) \{
71. e.printStackTrace();
72. 
73. \}
74. \}
75. 
76. public static void main(String\[\] args) throws Exception \{
77. Class.forName("com.mysql.jdbc.Driver").newInstance();
78. BlobTest test = new BlobTest();
79. test.con = java.sql.DriverManager.getConnection(
80. "jdbc:mysql://localhost:3306/test", "root", "123456");
81. test.createTable();
82. test.addBlob();
83. test.getBlob();
84. \}
85. \}

MySQL有四种BLOB类型:

·tinyblob:仅255个字符

·blob:最大限制到65K字节

·mediumblob:限制到16M字节

·longblob:可达4GB