使用JDBC过程中如何正确关闭connection

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来看一段代码：

import java.sql.*;/** * Created by N3verL4nd on 2017/4/17. */public class JdbcDemo{    public static void main(String[] args) {        Connection conn = null;        Statement stmt = null;        ResultSet rs = null;        String url = "jdbc:mysql://localhost:3306/weibo?"                + "user=root&password=lgh123&useUnicode=true&characterEncoding=UTF8&useSSL=true";        try {            Class.forName("com.mysql.jdbc.Driver");        } catch (ClassNotFoundException e) {            e.printStackTrace();        }        try {            conn = DriverManager.getConnection(url);            stmt = conn.createStatement();            /* System.out.println(sql); */            rs = stmt.executeQuery("SELECT * FROM t_account");            while (rs.next()){                System.out.println(rs.getString(2) + "  " + rs.getString(3) + "  " + rs.getString(4));            }            rs.close();System.out.println("ResultSet closed");            stmt.close();System.out.println("Statement closed");            conn.close();System.out.println("Connection closed");        } catch (SQLException e) {            e.printStackTrace();        }    }}

假如rs = stmt.executeQuery("SELECT * FROM s_account");我们查找一个不存在的表，就会出现异常：

而此时，

Connection conn = null;
Statement stmt = null;
ResultSet rs = null;都没有被正确关闭。

正确的处理方式应该是:在finally语句块中执行关闭操作。

Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;try {    // Do stuff    ...} catch (SQLException ex) {    // Exception handling stuff    ...} finally {    if (rs != null) {        try {            rs.close();        } catch (SQLException e) { /* ignored */}    }    if (ps != null) {        try {            ps.close();        } catch (SQLException e) { /* ignored */}    }    if (conn != null) {        try {            conn.close();        } catch (SQLException e) { /* ignored */}    }}

当然如果可以确保不是空指针，则可以简写为：

} finally {    try { rs.close(); } catch (Exception e) { /* ignored */ }    try { ps.close(); } catch (Exception e) { /* ignored */ }    try { conn.close(); } catch (Exception e) { /* ignored */ }}

这对于我们来时还是过于冗长，我们可以使用Apache Commons DbUtils 里的 DbUtils

} finally {    DbUtils.closeQuietly(rs);    DbUtils.closeQuietly(ps);    DbUtils.closeQuietly(conn);}

内部实现：

public static void close(ResultSet rs) throws SQLException {    if (rs != null) {        rs.close();    }}public static void close(Statement stmt) throws SQLException {    if (stmt != null) {        stmt.close();    }}public static void close(Connection conn) throws SQLException {    if (conn != null) {        conn.close();    }}public static void closeQuietly(Connection conn) {    try {        close(conn);    } catch (SQLException e) {        //e.printStackTrace();    }}public static void closeQuietly(ResultSet rs) {    try {        close(rs);    } catch (SQLException e) {        //e.printStackTrace();    }}public static void closeQuietly(Statement stmt) {    try {        close(stmt);    } catch (SQLException e) {        //e.printStackTrace();    }}public static void closeQuietly(Connection conn, Statement stmt, ResultSet rs) {    try {        closeQuietly(rs);    } finally {        try {            closeQuietly(stmt);        } finally {            closeQuietly(conn);        }    }}

参考：

http://stackoverflow.com/questions/2225221/closing-database-connections-in-java

http://www.cnblogs.com/hongten/archive/2011/03/29/1998311.html

http://www.cnblogs.com/jfqiu/p/3197014.html

https://shinesolutions.com/2007/08/04/how-to-close-jdbc-resources-properly-every-time/

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