oracle study notes (h) - and the result set metadata ResultSetMetaData ResultSet frame into corresponding entity class

Others 2019-09-19 20:51:28 views: null

 

Introduction

It may be used to obtain the object type and attribute information about the object ResultSet column block in the persistence layer framework: are widely (e.g. mybatis, hibernate) application.

Common method

  • int getColumnCount ()
    the number of columns in this ResultSet object Returns
  • String getColumnLabel (int column)
    recommended for the title of the specified column to obtain printouts and displays. It suggested that the title is usually specified by the SQL AS clause.

  • String getColumnName (int column)
    Gets the designated column's name

    Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select ename,job,hiredate from employee");
ResultSetMetaData resultSetMetaData = rs.getMetaData();
int colCount = resultSetMetaData.getColumnCount();
System.out.println("共有多少列：" + colCount);

for (int i = 1; i <= colCount; i++) {
    //得到列名
    String colLabel = resultSetMetaData.getColumnLabel(i);
    //通过列名得到该列的值
    Object value = rs.getObject(colLabel);
    System.out.println("第" + i + "列的值：" + value);
}

A simple example code frame

The following is a class, mainly about ResultSet returned by the database into corresponding entity class, pay attention, the name of the entity class property to keep the column names in the database matches
can be directly used

import java.lang.reflect.Field;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 将查询结果集的数据组装成相应的POJO(简单的Java对象)实体
 *
 * @author StarsOne
 * @date Create in  2019-4-27 0027 09:43:40
 * @description
 */
public class ResultSetHandler<T> {

    private List<T> beanList;
    private Class<T> type;
    private ResultSetMetaData metaData;
    private ResultSet resultSet;

    public ResultSetHandler(ResultSet resultSet, Class<T> type) {
        //初始化beanList
        beanList = new ArrayList<>();
        this.resultSet = resultSet;
        try {
            //获得数据集元数据
            this.metaData = resultSet.getMetaData();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        this.type = type;

        handlerData();

    }


    private void handlerData() {
        /*
        思路分析：
        1. 首先获得实体类中的所有属性：Class.getDeclareFields(),存放在Map<属性名,Field> 中
        2. 通过ResultSetMetaData结果集元数据中的列名，将查询结果相应的列的值取出来resultset.getObject()
        3. 将实体类的属性的名与结果集中相应的列进行反射赋值*/


        Field[] declaredFields = type.getDeclaredFields();
        Map<String, Field> fieldMap = new HashMap<>();
        for (Field declaredField : declaredFields) {
            //Map<"NUM",NUm属性对象>
            fieldMap.put(declaredField.getName().toUpperCase(), declaredField);
        }


        try {

            // while循环，遍历结果集ResultSet中的全部数据
            while (resultSet.next()) {
                //将一条数据对应的实体类对象添加到list中
                beanList.add(getT(fieldMap));
            }

        } catch (SQLException | IllegalAccessException | InstantiationException e) {
            e.printStackTrace();
        }

    }

    /**
     * 获得每一条数据所对应的一个实体类对象
     * @param fieldMap 存放属性field的Map集合
     * @return 一个实体类对象
     * @throws InstantiationException
     * @throws IllegalAccessException
     * @throws SQLException
     */
    private T getT(Map<String, Field> fieldMap) throws InstantiationException, IllegalAccessException, SQLException {
        // 获得查询结果中的列数
        int columnCount = metaData.getColumnCount();
        T target = type.newInstance();
        // 一次循环代表一列
        for (int i = 1; i <= columnCount; i++) {
            // 获得列的标题(列名）
            String columnLabel = metaData.getColumnLabel(i);
            // 检查此列是否有对应的属性存在
            if (fieldMap.containsKey(columnLabel)) {
                // 通过列名从Map中获得对应的Field对象
                Field field = fieldMap.get(columnLabel);
                field.setAccessible(true);

                //根据此属性的类型来调用相应的结果集方法，
                // 如：String ename --> resultSet.getString()
                Object value = null;
                Class<?> fieldType = field.getType();
                if (fieldType == String.class) { //Character
                    value = resultSet.getString(columnLabel);

                } else if (fieldType == Byte.class || fieldType == Byte.TYPE) { // int
                    value = resultSet.getByte(columnLabel);

                } else if (fieldType == Short.class || fieldType == Short.TYPE) { //
                    value = resultSet.getShort(columnLabel);

                } else if (fieldType == Integer.class || fieldType == Integer.TYPE) { //
                    value = resultSet.getInt(columnLabel);

                } else if (fieldType == Long.class || fieldType == Long.TYPE) { //
                    value = resultSet.getLong(columnLabel);

                } else if (fieldType == Double.class || fieldType == Double.TYPE) { //
                    value = resultSet.getDouble(columnLabel);

                } else if (fieldType == Float.class || fieldType == Float.TYPE) { //
                    value = resultSet.getFloat(columnLabel);

                } else if (fieldType == java.util.Date.class || fieldType == java.sql.Date.class) { //
                    value = resultSet.getDate(columnLabel);

                } else if (fieldType == java.sql.Time.class) { //
                    value = resultSet.getTime(columnLabel);

                } else if (fieldType == Boolean.class || fieldType == Boolean.TYPE) { //
                    value = resultSet.getBoolean(columnLabel);
                }

                field.set(target, value);
            } // end if
        } // end for
        return target;
    }

    /**
     * 获得list
     *
     * @return
     */
    public List<T> getBeanList() {
        return beanList;
    }
    
    public T getBean(){
        beanList!=null && beanList.size()>0?beanList.remove(0):null;
    }
    
}

 

Introduction

It may be used to obtain the object type and attribute information about the object ResultSet column block in the persistence layer framework: are widely (e.g. mybatis, hibernate) application.

Common method

  • int getColumnCount ()
    the number of columns in this ResultSet object Returns
  • String getColumnLabel (int column)
    recommended for the title of the specified column to obtain printouts and displays. It suggested that the title is usually specified by the SQL AS clause.

  • String getColumnName (int column)
    Gets the designated column's name

    Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("select ename,job,hiredate from employee");
ResultSetMetaData resultSetMetaData = rs.getMetaData();
int colCount = resultSetMetaData.getColumnCount();
System.out.println("共有多少列：" + colCount);

for (int i = 1; i <= colCount; i++) {
    //得到列名
    String colLabel = resultSetMetaData.getColumnLabel(i);
    //通过列名得到该列的值
    Object value = rs.getObject(colLabel);
    System.out.println("第" + i + "列的值：" + value);
}

A simple example code frame

The following is a class, mainly about ResultSet returned by the database into corresponding entity class, pay attention, the name of the entity class property to keep the column names in the database matches
can be directly used

import java.lang.reflect.Field;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * 将查询结果集的数据组装成相应的POJO(简单的Java对象)实体
 *
 * @author StarsOne
 * @date Create in  2019-4-27 0027 09:43:40
 * @description
 */
public class ResultSetHandler<T> {

    private List<T> beanList;
    private Class<T> type;
    private ResultSetMetaData metaData;
    private ResultSet resultSet;

    public ResultSetHandler(ResultSet resultSet, Class<T> type) {
        //初始化beanList
        beanList = new ArrayList<>();
        this.resultSet = resultSet;
        try {
            //获得数据集元数据
            this.metaData = resultSet.getMetaData();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        this.type = type;

        handlerData();

    }


    private void handlerData() {
        /*
        思路分析：
        1. 首先获得实体类中的所有属性：Class.getDeclareFields(),存放在Map<属性名,Field> 中
        2. 通过ResultSetMetaData结果集元数据中的列名，将查询结果相应的列的值取出来resultset.getObject()
        3. 将实体类的属性的名与结果集中相应的列进行反射赋值*/


        Field[] declaredFields = type.getDeclaredFields();
        Map<String, Field> fieldMap = new HashMap<>();
        for (Field declaredField : declaredFields) {
            //Map<"NUM",NUm属性对象>
            fieldMap.put(declaredField.getName().toUpperCase(), declaredField);
        }


        try {

            // while循环，遍历结果集ResultSet中的全部数据
            while (resultSet.next()) {
                //将一条数据对应的实体类对象添加到list中
                beanList.add(getT(fieldMap));
            }

        } catch (SQLException | IllegalAccessException | InstantiationException e) {
            e.printStackTrace();
        }

    }

    /**
     * 获得每一条数据所对应的一个实体类对象
     * @param fieldMap 存放属性field的Map集合
     * @return 一个实体类对象
     * @throws InstantiationException
     * @throws IllegalAccessException
     * @throws SQLException
     */
    private T getT(Map<String, Field> fieldMap) throws InstantiationException, IllegalAccessException, SQLException {
        // 获得查询结果中的列数
        int columnCount = metaData.getColumnCount();
        T target = type.newInstance();
        // 一次循环代表一列
        for (int i = 1; i <= columnCount; i++) {
            // 获得列的标题(列名）
            String columnLabel = metaData.getColumnLabel(i);
            // 检查此列是否有对应的属性存在
            if (fieldMap.containsKey(columnLabel)) {
                // 通过列名从Map中获得对应的Field对象
                Field field = fieldMap.get(columnLabel);
                field.setAccessible(true);

                //根据此属性的类型来调用相应的结果集方法，
                // 如：String ename --> resultSet.getString()
                Object value = null;
                Class<?> fieldType = field.getType();
                if (fieldType == String.class) { //Character
                    value = resultSet.getString(columnLabel);

                } else if (fieldType == Byte.class || fieldType == Byte.TYPE) { // int
                    value = resultSet.getByte(columnLabel);

                } else if (fieldType == Short.class || fieldType == Short.TYPE) { //
                    value = resultSet.getShort(columnLabel);

                } else if (fieldType == Integer.class || fieldType == Integer.TYPE) { //
                    value = resultSet.getInt(columnLabel);

                } else if (fieldType == Long.class || fieldType == Long.TYPE) { //
                    value = resultSet.getLong(columnLabel);

                } else if (fieldType == Double.class || fieldType == Double.TYPE) { //
                    value = resultSet.getDouble(columnLabel);

                } else if (fieldType == Float.class || fieldType == Float.TYPE) { //
                    value = resultSet.getFloat(columnLabel);

                } else if (fieldType == java.util.Date.class || fieldType == java.sql.Date.class) { //
                    value = resultSet.getDate(columnLabel);

                } else if (fieldType == java.sql.Time.class) { //
                    value = resultSet.getTime(columnLabel);

                } else if (fieldType == Boolean.class || fieldType == Boolean.TYPE) { //
                    value = resultSet.getBoolean(columnLabel);
                }

                field.set(target, value);
            } // end if
        } // end for
        return target;
    }

    /**
     * 获得list
     *
     * @return
     */
    public List<T> getBeanList() {
        return beanList;
    }
    
    public T getBean(){
        beanList!=null && beanList.size()>0?beanList.remove(0):null;
    }
    
}

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