QueryRunner類實戰

先上一個登錄代碼---判斷登錄是否成功

1、c3p0-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
    <default-config>
        <property name="user">root</property>
        <property name="password">123456</property>
        <property name="driverClass">com.mysql.jdbc.Driver</property>
        <property name="jdbcUrl">jdbc:mysql:///filter</property>
    </default-config> 
</c3p0-config> 

2.C3P0Utils

package com.ithiema.utils;

import com.mchange.v2.c3p0.ComboPooledDataSource;

import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class C3P0Utils {
//import com.mchange.v2.c3p0.ComboPooledDataSource;
    private static DataSource dataSource = new ComboPooledDataSource();

    private static ThreadLocal<Connection> tl = new ThreadLocal<Connection>();

    // 直接可以獲取一個連接池
    public static DataSource getDataSource() {
        return dataSource;
    }
    
    public static Connection getConnection() throws SQLException{
        return dataSource.getConnection();
    }

    // 獲取連接對象
    public static Connection getCurrentConnection() throws SQLException {

        Connection con = tl.get();
        if (con == null) {
            con = dataSource.getConnection();
            tl.set(con);
        }
        return con;
    }

    // 開啟事務
    public static void startTransaction() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.setAutoCommit(false);
        }
    }

    // 事務回滾
    public static void rollback() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.rollback();
        }
    }

    // 提交並且 關閉資源及從ThreadLocall中釋放
    public static void commitAndRelease() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.commit(); // 事務提交
            con.close();// 關閉資源
            tl.remove();// 從線程綁定中移除
        }
    }

    // 關閉資源方法
    public static void closeConnection() throws SQLException {
        Connection con = getCurrentConnection();
        if (con != null) {
            con.close();
        }
    }

    public static void closeStatement(Statement st) throws SQLException {
        if (st != null) {
            st.close();
        }
    }

    public static void closeResultSet(ResultSet rs) throws SQLException {
        if (rs != null) {
            rs.close();
        }
    }

}

3.UserDao.java

package com.ithiema.dao;

import com.ithiema.domain.User;
import com.ithiema.utils.C3P0Utils;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;

import java.sql.SQLException;

public class UserDao {

    public User login(String username, String password) throws SQLException {
        QueryRunner runner = new QueryRunner(C3P0Utils.getDataSource());
        String sql = "select * from user where username=? and password=?";
        return runner.query(sql, new BeanHandler<User>(User.class), username,password);
    }
}

 

QueryRunner類

QueryRunner中提供對sql語句操作的API
它主要有三個方法
　　query() 用於執行select
　　update() 用於執行insert/update/delete
　　batch() 批處理

1,Query語句
先來看下query的兩種形式, 我們這里主要講第一個方法, 因為我們用C3P0來統一管理connection.(QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource()))
query(sql,ResultSetHandler,Object...params);
query(conn,sql,ResultSetHandler,Object...params);

第一種: 不需要params

//查詢所有圖書
public List<Book> selectAllBooks() throws SQLException {
    QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
    return qr.query("select * from books", new BeanListHandler<Book>(Book.class));
}

 

第二種: 需要一個參數查詢

//根據id查詢指定的書
public Book selectBookById(String id) throws SQLException {
    QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
    return qr.query("select * from books where id=?", new BeanHandler(Book.class),id);
}

第三種:需要多個參數查詢

//多條件查詢圖書信息
public List<Book> findBookByManyCondition(String id, String category,
        String name, String minprice, String maxprice) throws SQLException {
    StringBuilder sql = new StringBuilder("select * from books where 1=1");
    List list = new ArrayList();
    if(!"".equals(id)){
        sql.append(" and id like ?");
        list.add("%"+id+"%");
    }
    if(!"".equals(category)){
        sql.append(" and category=?");
        list.add(category);
    }
    if(!"".equals(name)){
        sql.append(" and name like ?");
        list.add("%"+name+"%");
    }
    if(!"".equals(minprice)){
        sql.append(" and price > ?");
        list.add(minprice);
    }
    if(!"".equals(maxprice)){
        sql.append(" and price < ?");
        list.add(maxprice);
    }
    
    QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
    return qr.query(sql.toString(),new BeanListHandler<Book>(Book.class),list.toArray());
}

那么我們來看下源碼的實現: 
(1)QueryRunner.java

//第一種情況,無參數
public <T> T query(String sql, ResultSetHandler<T> rsh) throws SQLException {
    Connection conn = this.prepareConnection();

    return this.query(conn, true, sql, rsh, (Object[]) null);
}

//第二種和第三種使用同一方法: 需要參數
public <T> T query(String sql, ResultSetHandler<T> rsh, Object... params) throws SQLException {
    Connection conn = this.prepareConnection();

    return this.query(conn, true, sql, rsh, params);
}

解讀: 這里先是獲取connection, 利用this.preparaConnection() 獲取. 然后調用query()方法去執行查詢語句. 接下來看源碼是如何獲取到當前傳輸過來的connection以及query()方法的內部實現.

protected Connection prepareConnection() throws SQLException {
    if (this.getDataSource() == null) {
        throw new SQLException("QueryRunner requires a DataSource to be " +
            "invoked in this way, or a Connection should be passed in");
    }
    return this.getDataSource().getConnection();
}

這里很簡單, 因為我們用的C3P0數據庫連接池獲取的DataSource, 所以這里直就可以過去到當前的Connection.接下來就看下query()方法的內部實現. 

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;
}

解讀: 在這里可以看出, 無論是否有傳遞參數params, 都調用的是同一個query方法, 接着來看this.fillStatement(stmt, params);是如何將參數賦予preparedStatement中的. 

public void fillStatement(PreparedStatement stmt, Object... params) throws SQLException {

    // check the parameter count, if we can
    ParameterMetaData pmd = null;
    if (!pmdKnownBroken) {
        pmd = stmt.getParameterMetaData();
        int stmtCount = pmd.getParameterCount();
        int paramsCount = params == null ? 0 : params.length;

        if (stmtCount != paramsCount) {
            throw new SQLException("Wrong number of parameters: expected "
                    + stmtCount + ", was given " + paramsCount);
        }
    }

    // nothing to do here
    if (params == null) {
        return;
    }

    for (int i = 0; i < params.length; i++) {
        if (params[i] != null) {
            stmt.setObject(i + 1, params[i]);
        } else {
            // VARCHAR works with many drivers regardless
            // of the actual column type.  Oddly, NULL and
            // OTHER don't work with Oracle's drivers.
            int sqlType = Types.VARCHAR;
            if (!pmdKnownBroken) {
                try {
                    sqlType = pmd.getParameterType(i + 1);
                } catch (SQLException e) {
                    pmdKnownBroken = true;
                }
            }
            stmt.setNull(i + 1, sqlType);
        }
    }
}

這個方法就是核心所在. 
第一種情況: 當params為null的時候, 直接return然后執行sql語句.
第二種第三種情況: 當params不為null時, 循環遍歷傳入的params, 然后將params賦值到preparedStatement中, 然后填充占位符進行sql查詢. 這里我們也來回顧下直接使用preparedStatement來進行查詢的方式:

@Test
public void update(){
    Connection conn = null;
    PreparedStatement st = null;
    ResultSet rs = null;
    try{
        conn = JdbcUtils.getConnection();
        String sql = "update users set name=?,email=? where id=?";
        st = conn.prepareStatement(sql);
        st.setString(1, "gacl");
        st.setString(2, "[e-mail]");
        st.setInt(3, 2);
        int num = st.executeUpdate();
        if(num>0){
            System.out.println("更新成功！！");
        }
    }catch (Exception e) {
        e.printStackTrace();
        
    }finally{
        JdbcUtils.release(conn, st, rs);
    }
}

@Test
public void find(){
    Connection conn = null;
    PreparedStatement st = null;
    ResultSet rs = null;
    try{
        conn = JdbcUtils.getConnection();
        String sql = "select * from users where id=?";
        st = conn.prepareStatement(sql);
        st.setInt(1, 1);
        rs = st.executeQuery();
        if(rs.next()){
            System.out.println(rs.getString("name"));
        }
    }catch (Exception e) {
        
    }finally{
        JdbcUtils.release(conn, st, rs);
    }
}

2, Update語句
查看update語句:

//修改圖書 
public void updateBook(Book book) throws SQLException {
    QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
    qr.update(
            "UPDATE books SET NAME=? ,price=?,bnum=?,category=?,description=? WHERE id=?",
            book.getName(), book.getPrice(), book.getBnum(),
            book.getCategory(), book.getDescription(), book.getId())
}

接着是QueryRunner.java中的update 方法:

public int update(String sql, Object... params) throws SQLException {
    Connection conn = this.prepareConnection();

    return this.update(conn, true, sql, params);
}

private int update(Connection conn, boolean closeConn, String sql, 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");
    }

    PreparedStatement stmt = null;
    int rows = 0;

    try {
        stmt = this.prepareStatement(conn, sql);
        this.fillStatement(stmt, params);
        rows = stmt.executeUpdate();

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

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

    return rows;
}

到了參數賦值的時候又調用了上面的fillStatement方法, 這里就不再闡述了. 


3, Batch語句
這里直接看batch方法的實例, 然后結合源碼的實現.

//批量刪除
public void delBooks(String[] ids) throws SQLException {
    QueryRunner qr = new QueryRunner(C3P0Utils.getDataSource());
    Object[][] params = new Object[ids.length][];//高維確定執行sql語句的次數，低維是給？賦值
    for (int i = 0; i < params.length; i++) {
        params[i] = new Object[]{ids[i]};//給“？”賦值
    }
    qr.batch("delete from books where id=?", params);
}

然后看QueryRunner中的batch()方法:

public int[] batch(String sql, Object[][] params) throws SQLException {
    Connection conn = this.prepareConnection();

    return this.batch(conn, true, sql, params);
}

private int[] batch(Connection conn, boolean closeConn, String sql, 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 (params == null) {
        if (closeConn) {
            close(conn);
        }
        throw new SQLException("Null parameters. If parameters aren't need, pass an empty array.");
    }

    PreparedStatement stmt = null;
    int[] rows = null;
    try {
        stmt = this.prepareStatement(conn, sql);

        for (int i = 0; i < params.length; i++) {
            this.fillStatement(stmt, params[i]);
            stmt.addBatch();
        }
        rows = stmt.executeBatch();

    } catch (SQLException e) {
        this.rethrow(e, sql, (Object[])params);
    } finally {
        close(stmt);
        if (closeConn) {
            close(conn);
        }
    }

    return rows;
}

解讀: 因為params是一個二維數組, 所以往preparedStatement中賦值的時候使用了for循環, 然后通過preparedstatement.addBatch() 進行批量添加, 然后執行executeBatch()進行操作.

　　 /**
     * Adds a set of parameters to this <code>PreparedStatement</code>
     * object's batch of commands.
     *
     * @exception SQLException if a database access error occurs or
     * this method is called on a closed <code>PreparedStatement</code>
     * @see Statement#addBatch
     * @since 1.2
     */
    void addBatch() throws SQLException;