Java连接数据库 #04# Apache Commons DbUtils

索引

1. 通过一个简单的调用看整体结构
2. Examples
3. 修改JAVA连接数据库 #03# HikariCP中的代码

DbUtils并非是什么ORM框架，只是对原始的JDBC进行了一些封装，以便我们少写一些重复代码。就“用”而言，仅仅需要学习QueryRunner类和ResultSetHandler接口就可以了。它的显著特点就是超级轻量级，总代码量目测似乎还不到一万行。

通过一个简单的调用看整体结构

public class TestDbUtils {
    private static final QueryRunner RUNNER = new QueryRunner(HikariCPUtils.getDs());
    public static void main(String[] args) {
        ResultSetHandler<SimpleUser> handler = new BeanHandler<>(SimpleUser.class);
        SimpleUser user = null;
        try {
            user = RUNNER.query("SELECT * FROM simple_user WHERE username=?", handler, "admin123");
        } catch (SQLException e) {
            e.printStackTrace();
        }
        System.out.println(user);
    }
}

TestDbUtils.java

    /**
     * Calls query after checking the parameters to ensure nothing is null.
     * @param conn The connection to use for the query call.
     * @param closeConn True if the connection should be closed, false otherwise.
     * @param sql The SQL statement to execute.
     * @param params An array of query replacement parameters.  Each row in
     * this array is one set of batch replacement values.
     * @return The results of the query.
     * @throws SQLException If there are database or parameter errors.
     */
    private <T> T query(Connection conn, boolean closeConn, String sql, ResultSetHandler<T> rsh, Object... params)
            throws SQLException {
        if (conn == null) {
            throw new SQLException("Null connection");
        }

        if (sql == null) {
            if (closeConn) {
                close(conn);
            }
            throw new SQLException("Null SQL statement");
        }

        if (rsh == null) {
            if (closeConn) {
                close(conn);
            }
            throw new SQLException("Null ResultSetHandler");
        }

        PreparedStatement stmt = null;
        ResultSet rs = null;
        T result = null;

        try {
            stmt = this.prepareStatement(conn, sql);
            this.fillStatement(stmt, params);
            rs = this.wrap(stmt.executeQuery());
            result = rsh.handle(rs);

        } catch (SQLException e) {
            this.rethrow(e, sql, params);

        } finally {
            try {
                close(rs);
            } finally {
                close(stmt);
                if (closeConn) {
                    close(conn);
                }
            }
        }

        return result;
    }

private T query(Connection conn, boolean closeConn, String sql, ResultSetHandler rsh, Object... params) throws SQLException

AbstractQueryRunner、RowProcessor、ResultSetHandler<T>是Apache Commons DbUtils里的三大主角，通过继承上述抽象类/实现上述接口可以很方便地对API功能进行定制化。另外，想用好DbUtils的话，感觉QueryRunner类和DbUtils类的源码应该是需要经常参照的，通过这两个类可以完成大部分事情，并且灵活度很高。

详细类图参考：http://ju.outofmemory.cn/entry/143920

Examples

官方Examples：http://commons.apache.org/proper/commons-dbutils/examples.html

同步请求的代码在上面已经给出。异步请求的草稿代码如下：

public class DbUtilsSampleDAO {

    private AsyncQueryRunner runner = new AsyncQueryRunner(Executors.newCachedThreadPool());

    public Future<Integer> saveProfile(Profile profile) {
        Future<Integer> future;
        Connection conn = null;
        try {
            conn = ConnectionFactory.getConnection();
            future = runner.update(conn,
                    "INSERT ignore INTO `profiles`.`profile` (`username`, `password`, `nickname`) " +
                            "VALUES (?, ?, ?)", profile.getUsername(), profile.getPassword(), profile.getNickname());
        } catch (SQLException e) {
            throw new DaoException(e);
        } finally {
            try {
                DbUtils.close(conn);
            } catch (SQLException e) {
                throw new DaoException(e);
            }
        }
        return future;
    }

    public static void main(String[] args) {
        DbUtilsSampleDAO dao = new DbUtilsSampleDAO();
        Profile profile = new Profile("myusername", "mypassword", "thisnickname");
        Future<Integer> future = dao.saveProfile(profile);
        try {
            System.out.println(future.get() == 1 ? "更新成功" : "更新失败");
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
    }
}

修改JAVA连接数据库 #03# HikariCP中的代码

同步更新在GitHub：https://github.com/xkfx/web-test-01

主要的几个类如下：

① QueryRunnerProxy.java

package org.sample.webapp.db.queryrunner;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.ResultSetHandler;
import org.sample.webapp.db.connmanager.ConnectionFactory;
import org.sample.webapp.exception.DaoException;

import java.sql.SQLException;

/**
 * 封装DAO层通用代码，不会关闭connection！！！
 */
public class QueryRunnerProxy {

    private QueryRunnerProxy() {
        // Exists to defeat instantiation
    }

    private static QueryRunner runner = new QueryRunner();

    public static int update(String sql, Object... param) {
        int updates = 0;
        try {
            updates = runner.update(ConnectionFactory.getConnection(), sql, param);
        } catch (SQLException e) {
            throw new DaoException(e);
        }
        return updates;
    }

    public static <T> T query(String sql, ResultSetHandler<T> rsh, Object... params) {
        T result = null;
        try {
            result = runner.query(ConnectionFactory.getConnection(), sql, rsh, params);
        } catch (SQLException e) {
            throw new DaoException(e);
        }
        return result;
    }
}

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② RsHandlers.java

package org.sample.webapp.db.queryrunner;

import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.sample.webapp.entity.Profile;

/**
 * 业务相关，保存各式各样的ResultSetHandler常量
 */
public interface RsHandlers {

    BeanListHandler<Profile> PROFILE_LIST = new BeanListHandler<>(Profile.class);

    BeanHandler<Profile> PROFILE = new BeanHandler<>(Profile.class);
}

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③ ProfileDAOImpl.java 顺便改为enum了，仅是因为感觉这样写表示单例更清晰。

package org.sample.webapp.dao.impl;

import org.sample.webapp.dao.ProfileDAO;
import org.sample.webapp.db.queryrunner.QueryRunnerProxy;
import org.sample.webapp.db.queryrunner.RsHandlers;
import org.sample.webapp.entity.Profile;

import java.util.List;

/**
 * 该类方法统一抛出DaoException
 */
public enum ProfileDAOImpl implements ProfileDAO {

    INSTANCE;

    @Override
    public int saveProfile(Profile profile) {
        final String sql = "INSERT ignore INTO profile (username, password, nickname) " +
                "VALUES (?, ?, ?)"; // 添加ignore出现重复不会抛出异常而是返回0
        return QueryRunnerProxy.update(sql, profile.getUsername(), profile.getPassword(), profile.getNickname());
    }

    @Override
    public List<Profile> listByNickname(String nickname) {
        final String sql = "SELECT  profile_id AS id,  username,  password,  nickname, last_online AS lastOnline, gender, birthday, location, joined " +
                "FROM profile " +
                "WHERE nickname=?";
        return QueryRunnerProxy.query(sql, RsHandlers.PROFILE_LIST, nickname);
    }

    @Override
    public Profile getByUsername(String username) {
        final String sql = "SELECT  profile_id AS id,  username,  password,  nickname, last_online AS lastOnline, gender, birthday, location, joined " +
                "FROM profile " +
                "WHERE username=?"; // TODO 该字符串会反复创建吗？
        return QueryRunnerProxy.query(sql, RsHandlers.PROFILE, username);
    }

    @Override
    public int updateById(Profile profile) {
        final String sql = "UPDATE profile " +
                "SET nickname=?, gender=?, birthday=?, location=? " +
                "WHERE profile_id=?";
        return QueryRunnerProxy.update(sql, profile.getNickname(), profile.getGender() != null ? String.valueOf(profile.getGender()) : null,
                profile.getBirthday(), profile.getLocation(), profile.getId());
    }

    @Override
    public int updatePassword(String username, String password) {
        final String sql = "UPDATE profile " +
                "SET password=? " +
                "WHERE username=?";
        return QueryRunnerProxy.update(sql, password, username);
    }

    @Override
    public int updateLastOnline(String username) {
        final String sql = "UPDATE profile " +
                "SET last_online=CURRENT_TIMESTAMP " +
                "WHERE username=?";
        return QueryRunnerProxy.update(sql, username);
    }
}

原文地址：https://www.cnblogs.com/xkxf/p/10128082.html