這裏是Main.java
:是否有更簡潔的方式來使用try-with-resource和PreparedStatement?
package foo.sandbox.db;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class Main {
public static void main(String[] args) {
final String SQL = "select * from NVPAIR where name=?";
try (
Connection connection = DatabaseManager.getConnection();
PreparedStatement stmt = connection.prepareStatement(SQL);
DatabaseManager.PreparedStatementSetter<PreparedStatement> ignored = new DatabaseManager.PreparedStatementSetter<PreparedStatement>(stmt) {
@Override
public void init(PreparedStatement ps) throws SQLException {
ps.setString(1, "foo");
}
};
ResultSet rs = stmt.executeQuery()
) {
while (rs.next()) {
System.out.println(rs.getString("name") + "=" + rs.getString("value"));
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
這裏是DatabaseManager.java
package foo.sandbox.db;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.Statement;
/**
* Initialize script
* -----
* CREATE TABLE NVPAIR;
* ALTER TABLE PUBLIC.NVPAIR ADD value VARCHAR2 NULL;
* ALTER TABLE PUBLIC.NVPAIR ADD id int NOT NULL AUTO_INCREMENT;
* CREATE UNIQUE INDEX NVPAIR_id_uindex ON PUBLIC.NVPAIR (id);
* ALTER TABLE PUBLIC.NVPAIR ADD name VARCHAR2 NOT NULL;
* ALTER TABLE PUBLIC.NVPAIR ADD CONSTRAINT NVPAIR_name_pk PRIMARY KEY (name);
*
* INSERT INTO NVPAIR(name, value) VALUES('foo', 'foo-value');
* INSERT INTO NVPAIR(name, value) VALUES('bar', 'bar-value');
*/
public class DatabaseManager {
/**
* Class to allow PreparedStatement to initialize parmaters inside try-with-resource
* @param <T> extends Statement
*/
public static abstract class PreparedStatementSetter<T extends Statement> implements AutoCloseable {
public PreparedStatementSetter(PreparedStatement pstmt) throws SQLException {
init(pstmt);
}
@Override
public void close() throws Exception {
}
public abstract void init(PreparedStatement pstmt) throws SQLException;
}
/* Use local file for database */
private static final String JDBC_CONNECTION = "jdbc:h2:file:./db/sandbox_h2.db;MODE=PostgreSQL";
static {
try {
Class.forName("org.h2.Driver"); // Init H2 DB driver
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* @return Database connection
* @throws SQLException
*/
public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(JDBC_CONNECTION, "su", "");
}
}
我使用H2數據庫簡單,因爲它是一個基於文件的一個,很容易創建和測試上。
所以一切工作和資源得到清理不如預期,但我只是覺得有可能是設定與嘗試,與資源塊內的PreparedStatement
參數的更清潔的方式(我不想使用嵌套嘗試/抓住塊看起來'尷尬')。也許在JDBC中已經存在一個助手類來做到這一點,但我一直沒有找到。
最好用一個lambda函數來初始化PreparedStatement
,但它仍然需要分配一個AutoCloseable
對象,以便它可以在try-with-resources中。
[我應該如何在JDBC中使用try-with-resources?](http://stackoverflow.com/questions/8066501/how-should-i-use-try-with-resources-with-jdbc ) –
我希望找到一種方法來使用lambda代替類實例來完成PreparedStatement的init,就像將參數傳入PreparedStatement一樣。 – AlexC