mybatis框架分析之实现自己的framework(加篇)

package com.eleven.session;


import com.eleven.config.*;


import javax.sql.DataSource;
import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.util.ArrayList;
import java.util.List;


/**
 * sql执行器默认实现类
 * @author eleven
 * @see
 * @since
 */


public class SimpleExecutor implements Executor {


    private static final String PREPARED = "prepared";


    @Override
    public List<Object> query(Configuration configuration, MappedStatement mappedStatement, Object param) {
        List<Object> results = new ArrayList<>();
        Connection connection = null;
        try {
            // 获取连接
            // 先从Configuration对象中获取DataSource（到底是C3P0还是Dbcp还是其他的）
            DataSource dataSource = configuration.getDataSource();
            // 从DataSource获取连接
            connection = dataSource.getConnection();
            // 执行Statement
            // 先从Configuration对象中根据statementId获取MappedStatement对象（SQL语句等）
            String statementType = mappedStatement.getStatementType();
            statementType = statementType == null || statementType.equals("") ? "prepared" : statementType;
            if (PREPARED.equals(statementType)) {
                handlePreparedStatement(results, mappedStatement, connection, param);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return results;
    }


    private void handlePreparedStatement(List<Object> results, MappedStatement mappedStatement, Connection connection,
                                         Object param) throws Exception {
        // 通过MappedStatement对象，获取SQL语句（需要特殊处理）
        BoundSql boundSql = getBoundSql(mappedStatement, param);
        // 通过MappedStatement对象，获取statementType字段
        // 创建Statement（JDBC包含三种Statement：Statement、PreparedStatement、CallableStatement）
        PreparedStatement statement = connection.prepareStatement(boundSql.getSql());
        // 设置参数
        // 获取SQL语句对应的参数信息List<ParameterMapping>
        handleParameter(statement, param, boundSql.getParameterMappings());
        // 执行statement
        ResultSet resultSet = statement.executeQuery();
        // 处理结果
        Class<?> resultTypeClass = mappedStatement.getResultType();
        handleReturnValue(results, resultSet, resultTypeClass);
    }


    private void handleReturnValue(List<Object> results, ResultSet resultSet, Class<?> resultTypeClass)
            throws Exception {
        while (resultSet.next()) {
            Object result = resultTypeClass.newInstance();
            ResultSetMetaData metaData = resultSet.getMetaData();
            int columnCount = metaData.getColumnCount();


            for (int i = 1; i <= columnCount; i++) {
                String columnName = metaData.getColumnName(i);
                Field field = resultTypeClass.getDeclaredField(columnName);
                field.setAccessible(true);
                field.set(result, resultSet.getObject(columnName));
            }
            results.add(result);
        }
    }


    private void handleParameter(PreparedStatement statement, Object param, List<ParameterMapping> parameterMappings)
            throws Exception {
        if (param instanceof Integer) {
            statement.setObject(1, param);
        } else if (param instanceof String) {
            statement.setObject(1, param);
        } else {
            Class<?> clazz = param.getClass();
            for (int i = 0; i < parameterMappings.size(); i++) {
                ParameterMapping parameterMapping = parameterMappings.get(i);
                String name = parameterMapping.getName();
                Field field = clazz.getDeclaredField(name);
                field.setAccessible(true);
                Object value = field.get(param);
                statement.setObject(i + 1, value);
            }
        }
    }


    private BoundSql getBoundSql(MappedStatement mappedStatement, Object param) {
        SqlSource sqlSource = mappedStatement.getSqlSource();
        return sqlSource.getBoundSql();
    }
}