Java - 线程“主”java.lang.Error 中的异常：未解决的编译问题

Posted 2023-02-24

【中文标题】Java - 线程“主”java.lang.Error 中的异常：未解决的编译问题

【英文标题】：Java - Exception in thread "main" java.lang.Error: Unresolved compilation problems

【发布时间】：2012-06-28 18:23:53

【问题描述】：

我的 JDBC 代码有一些问题。我正在尝试通过 mysql 连接，但它给了我一个错误。如果您有时间，我的错误日志如下所示。

Exception in thread "main" java.lang.Error: Unresolved compilation problems: 
    BLOB cannot be resolved to a type
    BLOB cannot be resolved to a type

    at serialize.SerializeDeserialze.main(SerializeDeserialze.java:73)

我的代码如下。我正在使用mysql-connector-java-5.1.20.jar驱动程序：

package serialize;
/*
 By vivek
*/

import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import oracle.sql.BLOB;

/****
CREATE TABLE java_objects (object_id NUMBER, object_name varchar(128), object_value BLOB DEFAULT empty_blob(), primary key (object_id));
SQL> desc java_objects;
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 OBJECT_ID                                 NOT NULL NUMBER
 OBJECT_NAME                                        VARCHAR2(128)
 OBJECT_VALUE                                       BLOB

SQL> select SEQUENCE_NAME, MIN_VALUE, MAX_VALUE, INCREMENT_BY, LAST_NUMBER from  user_sequences;

SEQUENCE_NAME                   MIN_VALUE  MAX_VALUE INCREMENT_BY LAST_NUMBER
------------------------------ ---------- ---------- ------------ -----------
ID_SEQ                                  1 1.0000E+27            1          21
JAVA_OBJECT_SEQUENCE                    1 1.0000E+27            1           1

*/
public class SerializeDeserialze 
  public static void main(String[] args) throws Exception 
    String WRITE_OBJECT_SQL = "BEGIN "
        + "  INSERT INTO java_objects(object_id, object_name, object_value) "
        + "  VALUES (?, ?, empty_blob()) " + "  RETURN object_value INTO ?; " + "END;";
    String READ_OBJECT_SQL = "SELECT object_value FROM java_objects WHERE object_id = ?";

    Connection conn = getOracleConnection();
    conn.setAutoCommit(false);
    List<Object> list = new ArrayList<Object>();
    list.add("This is a short string.");
    list.add(new Integer(1234));
    list.add(new java.util.Date());

    // write object to Oracle
    long id = 0001;
    String className = list.getClass().getName();
    CallableStatement cstmt = conn.prepareCall(WRITE_OBJECT_SQL);

    cstmt.setLong(1, id);
    cstmt.setString(2, className);

    cstmt.registerOutParameter(3, java.sql.Types.BLOB);

    cstmt.executeUpdate();
    BLOB blob = (BLOB) cstmt.getBlob(3);
    OutputStream os = blob.getBinaryOutputStream();
    ObjectOutputStream oop = new ObjectOutputStream(os);
    oop.writeObject(list);
    oop.flush();
    oop.close();
    os.close();

    // Read object from oracle
    PreparedStatement pstmt = conn.prepareStatement(READ_OBJECT_SQL);
    pstmt.setLong(1, id);
    ResultSet rs = pstmt.executeQuery();
    rs.next();
    InputStream is = rs.getBlob(1).getBinaryStream();
    ObjectInputStream oip = new ObjectInputStream(is);
    Object object = oip.readObject();
    className = object.getClass().getName();
    oip.close();
    is.close();
    rs.close();
    pstmt.close();
    conn.commit();

    // de-serialize list a java object from a given objectID
    List listFromDatabase = (List) object;
    System.out.println("[After De-Serialization] list=" + listFromDatabase);
    conn.close();
  

  private static Connection getHSQLConnection() throws Exception 
    Class.forName("org.hsqldb.jdbcDriver");
    System.out.println("Driver Loaded.");
    String url = "jdbc:hsqldb:data/tutorial";
    return DriverManager.getConnection(url, "sa", "");
  

  public static Connection getMySqlConnection() throws Exception 
    String driver = "org.gjt.mm.mysql.Driver";
    String url = "jdbc:mysql://localhost/demo2s";
    String username = "oost";
    String password = "oost";

    Class.forName(driver);
    Connection conn = DriverManager.getConnection(url, username, password);
    return conn;
  

  public static Connection getOracleConnection() throws Exception 
    String driver = "oracle.jdbc.driver.OracleDriver";
    String url = "jdbc:oracle:thin:@localhost:1521:databaseName";
    String username = "userName";
    String password = "password";

    Class.forName(driver); // load Oracle driver
    Connection conn = DriverManager.getConnection(url, username, password);
    return conn;
  

【问题讨论】：

你的类路径中有 oracle jar 吗？

不，我只将 mysql jar 放在我的类路径中.....

【参考方案1】：

当您使用 Eclipse 作为 IDE 并尝试运行甚至无法编译的代码时会发生此错误。检查 Eclipse 中的 Problems 视图，并在执行应用程序之前修复编译错误。

【讨论】：

谢谢，就是这样。当我在 package 语句之前添加一个 import 语句时，这发生在我身上。

【参考方案2】：

您正在使用 MySQL 驱动程序，但您的类使用 Oracle BLOB 类。要么使用 Oracle JDBC 驱动程序，要么为 BLOB 使用不同的类。

由于您的代码提到了 HSQL、MySQL 和 Oracle，您可能希望摆脱特定于 Oracle 的 BLOB 实现。