DBUtils源码分析

标签：数据库   dbutils   源码   query   

其实,在这篇文章里,我只是分析了dbutis的query的运作流程。

至于类为什么要这样设计,蕴含的设计模式等等高级知识点咱们在下节再探讨。

先看看最简单的DBUtils是如何工作的。

package dbutils;

import model.Student;

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.ResultSetHandler;
import org.junit.Test;

import java.sql.SQLException;

public class BeanExample {

    @Test
    public void testBean() {
    
        QueryRunner qr = new QueryRunner(new MyDBSource());

        String sql = "select * from student where xh=?";
        Object params[] = { "02" };
        Student s=null;
        try {
            ResultSetHandler<Student> rsh=new BeanHandler<>(Student.class);
            s =  qr.query(sql,rsh,params);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println(s.getXm());

    }

}

public class MyDBSource implements DataSource {

    private static String driverClassName = "com.mysql.jdbc.Driver";
    private static String url = "jdbc:mysql://localhost:3306/webexample";

    private static String userName = "root";
    private static String passWord = "root";
    
    @Override
    public Connection getConnection() throws SQLException {
        try {
            Class.forName(driverClassName);
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return DriverManager.getConnection(url, userName, passWord);

    }
    //....
}

    //BeanHandler.java
    public BeanHandler(Class<T> type) {
        this(type, ArrayHandler.ROW_PROCESSOR);
    }
    public BeanHandler(Class<T> type, RowProcessor convert) {
        this.type = type;
        this.convert = convert;
    }

    //ArrayHandler.java
    public class ArrayHandler implements ResultSetHandler<Object[]> {
         static final RowProcessor ROW_PROCESSOR = new BasicRowProcessor();
          //....
    }

    //BasicRowProcessor.java
    public class BasicRowProcessor implements RowProcessor {
      private static final BeanProcessor defaultConvert = new BeanProcessor();
         
      public BasicRowProcessor() {
             this(defaultConvert);
          }
      //...
    }

    s =  qr.query(sql,rsh,params);

我们看时序图

       protected PreparedStatement prepareStatement(Connection conn, String sql)
            throws SQLException {
        return conn.prepareStatement(sql);
    }

     for (int i = 0; i < params.length; i++) {
            if (params[i] != null) {
                stmt.setObject(i + 1, params[i]);
            }
        //...
     }

     BeanHandler.java
     public T handle(ResultSet rs) throws SQLException {
        return rs.next() ? this.convert.toBean(rs, this.type) : null;
      }

    public <T> T toBean(ResultSet rs, Class<T> type) throws SQLException {
        PropertyDescriptor[] props = this.propertyDescriptors(type);
        ResultSetMetaData rsmd = rs.getMetaData();
        int[] columnToProperty = this.mapColumnsToProperties(rsmd, props);

        return this.createBean(rs, type, props, columnToProperty);
    }

      //对源码略微有删改
      //但绝对不影响核心思想
      private <T> T createBean(ResultSet rs, Class<T> type,
            PropertyDescriptor[] props, int[] columnToProperty)
            throws SQLException {

        T bean = this.newInstance(type);

        for (int i = 1; i < columnToProperty.length; i++) {

            PropertyDescriptor prop = props[columnToProperty[i]];
            Class<?> propType = prop.getPropertyType();

            Object value = null;
            if(propType != null)
                value = this.processColumn(rs, i, propType);

            this.callSetter(bean, prop, value);
        }

        return bean;
    }

                // Don't call setter if the value object isn't the right type
            if (this.isCompatibleType(value, params[0])) {
                setter.invoke(target, new Object[]{value});
            } else {
              throw new SQLException(
                  "Cannot set " + prop.getName() + ": incompatible types, cannot convert "
                  + value.getClass().getName() + " to " + params[0].getName());
                  // value cannot be null here because isCompatibleType allows null
            }

DBUtils源码分析

标签：数据库   dbutils   源码   query   

原文地址：http://blog.csdn.net/dlf123321/article/details/45172429