使用java反射将结果集封装成为对象和对象集合操作

Z时代
2024-01-10
分类：综合

java反射机制是什么

反射机制是在运行状态中，可以知道任何一个类的属性和方法，并且调用类的属性和方法；

反射机制能够做什么

1、判断运行对象的所属类

2、构造任意一个类的对象

3、获取任意一个类的属性和方法

4、调用任意属性和方法

5、生成动态代理

利用反射将结果集封装成为对象或者集合(实测可用)


package coral.base.util;
import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import wfc.service.database.RecordSet;
public class ReflectUtils {
  /**
   * 将一个map集合封装成为bean对象
   * 
   * @param param
   * @param clazz
   * @return
   */
  public static <T> T MapToBean(Map<String, Object> param, Class<?> clazz) {
    Object value = null;
    Class[] paramTypes = new Class[1];
    Object obj = null;
    try {
      obj = clazz.newInstance();
      // 获取类的属性
      Field[] declaredFields = clazz.getDeclaredFields();
      // 获取父类或接口的公有属性
      Field[] superFields = clazz.getSuperclass().getFields();
      List<Field[]> list = new ArrayList<Field[]>();
      if (declaredFields != null) {
        list.add(declaredFields);
      }
      if (superFields != null) {
        list.add(superFields);
      }
      for (Field[] fields : list) {
        for (Field field : fields) {
          String fieldName = field.getName();
          // 获取属性对应的值ֵ
          value = param.get(fieldName);
          // 把值设置进入对象属性中 这里可能是有属性但是没有相应的set方法，所以要做异常处理
          try {
            PropertyDescriptor pd = new PropertyDescriptor(
                fieldName, clazz);
            Method method = pd.getWriteMethod();
            method.invoke(obj, new Object[] { value });
          } catch (Exception e1) {
          }
        }
      }
    } catch (Exception e1) {
    }
    return (T) obj;
  }
  /**
   * 获取类的所有属性，包括父类和接口
   * @param clazz
   * @return
   */
  public static List<Field[]> getBeanFields(Class<?> clazz) {
    List<Field[]> list = new ArrayList<Field[]>();
    Field[] declaredFields = clazz.getDeclaredFields();
    Field[] superFields = clazz.getSuperclass().getFields();
    if (declaredFields != null) {
      list.add(declaredFields);
    }
    if (superFields != null) {
      list.add(superFields);
    }
    return list;
  }
  /**
   * 从结果集中获取出值
   * @param fieldName
   * @param rs
   * @return
   */
  public static Object getFieldValue(String fieldName, ResultSet rs) {
    Object value = null;
    try {
      //捕获值不存在的异常
      value = rs.getObject(fieldName);
      return value;
    } catch (SQLException e) {
      //oracle数据库的列都是大写，所以才查找一次
      fieldName = fieldName.toLowerCase();
      try {
        value = rs.getObject(fieldName);
        return value;
      } catch (SQLException e1) {
        //结果集中没有对应的值，返回为空
        return null;
      }
    }
  }
  /**
   * 方法重载，
   * @param fieldName
   * @param rs 这个是封装过的结果集
   * @return
   */
  public static Object getFieldValue(String fieldName, RecordSet rs) {
    Object value = null;
    value = rs.getObject(fieldName);
    return value;
  }
  /**
   * 方法重载
   * @param rs 封装过的结果集
   * @param clazz
   * @return
   */
  public static <T> T RSToBean(RecordSet rs, Class<?> clazz) {
    Object obj = null;
    List<Field[]> list = getBeanFields(clazz);
    try {
      obj = clazz.newInstance();
      for (Field[] fields : list) {
        for (Field field : fields) {
          String fieldName = field.getName();
          // String fieldName = field.getName();ֵ
          Object value = getFieldValue(fieldName, rs);
          try {
            PropertyDescriptor pd = new PropertyDescriptor(
                fieldName, clazz);
            Method method = pd.getWriteMethod();
            method.invoke(obj, new Object[] { value });
          } catch (Exception e1) {
          }
        }
      }
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return (T) obj;
  }
  /**
   * 把结果集封装成为bean对象
   * @param rs
   * @param clazz
   * @return
   */
  public static <T> T RSToBean(ResultSet rs, Class<?> clazz) {
    Object obj = null;
    List<Field[]> list = getBeanFields(clazz);
    try {
      while (rs.next()) {
        obj = clazz.newInstance();
        for (Field[] fields : list) {
          for (Field field : fields) {
            String fieldName = field.getName();
            // String fieldName = field.getName();ֵ
            Object value = getFieldValue(fieldName, rs);
            PropertyDescriptor pd = new PropertyDescriptor(
                fieldName, clazz);
            Method method = pd.getWriteMethod();
            method.invoke(obj, new Object[] { value });
          }
        }
      }
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return (T) obj;
  }
  /**
   * 把结果集封装成为List
   * 
   * @param rs
   * @param clazz
   * @return
   */
  public static <T> List<T> RsToList(ResultSet rs, Class<?> clazz) {
    ArrayList<T> objList = new ArrayList<T>();
    // 获取所有的属性
    List<Field[]> list = getBeanFields(clazz);
    try {
      while (rs.next()) {
        // 定义临时变量
        Object tempObeject = clazz.newInstance();
        // 添加到属性中
        for (Field[] fields : list) {
          for (Field field : fields) {
            String fieldName = field.getName();
            // 获取属性值ֵ
            Object value = getFieldValue(fieldName, rs);
            PropertyDescriptor pd = new PropertyDescriptor(
                fieldName, clazz);
            Method method = pd.getWriteMethod();
            method.invoke(tempObeject, new Object[] { value });
          }
        }
        objList.add((T) tempObeject);
      }
    } catch (Exception e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return objList;
  }
}

补充知识：java反射自动封装值到实体类

1.工具类


package com.util;
import com.entity.Student;
import javax.servlet.ServletRequest;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.text.SimpleDateFormat;
import java.util.Enumeration;
/**
 * Created by wq on 2017/8/30.
 */
public class BeanOperateTools {
  /*
  利用反射进行所以请求参数的设置，要求参数名与属性名一致
   */
  /**
   *
   * @param obj
   * @param req
   * @param datePatern 将字符串变为日期时间格式化的字符串
   * @throws Exception
   */
  public static void setValue(Object obj, ServletRequest req,String datePatern)
      throws Exception {//设置属性的内容
    {
      System.out.println("进了setValue方法.....");
      //取得class对象
      Class<?> cls = obj.getClass();
      //取得输入的全部参数名称
      Enumeration<String> enu = req.getParameterNames();
      //循环输入的全部参数名称
      while (enu.hasMoreElements()) {
        String paramName = enu.nextElement();//取得参数名称
        String paramValue = req.getParameter(paramName);
      //取得属性的类型是为了取得参数的类型，以确定method方法和是否转型
        Field field = cls.getDeclaredField(paramName); //取得指定名称的属性 (实体类里面
        //取得指定的操作方法，以满足反射调用
        Method method = cls.getMethod("set"+StringTools.initcap(paramName),field.getType());
        //根据类型进行数据的转换，同时调用setter设置数据
        //取得类型
        String fieldType=field.getType().getSimpleName();
        if ("string".equalsIgnoreCase(fieldType)) {
          method.invoke(obj,paramValue);
        }else if ("integer".equalsIgnoreCase(fieldType)||"int".equalsIgnoreCase(fieldType)){
          method.invoke(obj,Integer.parseInt(paramValue));
        }else if ("double".equalsIgnoreCase(fieldType)){
          method.invoke(obj,Double.parseDouble(paramValue));
        }else if ("date".equalsIgnoreCase(fieldType)){
          method.invoke(obj,new SimpleDateFormat(datePatern).parse(paramValue));
        }
      }
    }
  }
}

2.servlet中调用此方法


package com.servlet;
import com.entity.Student;
import com.sun.xml.internal.bind.v2.runtime.reflect.opt.FieldAccessor_Double;
import com.util.BeanOperateTools;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Enumeration;
/**
 * Created by wq on 2017/8/22.
 */
@WebServlet(name = "studentServlet", urlPatterns = {"/StudentServlet"})
public class StudentServlet extends HttpServlet {
  //private Student stu = new Student();
  private Student student=new Student();
  public Student getStudent() {
    return student;
  }
  public void setStudent(Student student) {
    this.student = student;
  }
-------此处模仿依赖注入
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    req.setCharacterEncoding("UTF-8");
    try {
      BeanOperateTools.setValue(this.getStudent(),req,"yyyy-MM-dd");
    } catch (Exception e) {
      e.printStackTrace();
    }
    req.setAttribute("student",this.student);
    req.getRequestDispatcher("student_insert_do.jsp").forward(req,resp);
    // Class<?> cls= this.stu.getClass();
  }
  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    this.doGet(req, resp);
  }
  public String initcap(String str) {//首字母大写
    return str.substring(0, 1).toUpperCase().concat(str.substring(1).toLowerCase());
  }
}

3.新增学生的jsp页面


<%--
 Created by IntelliJ IDEA.
 User: wq
 Date: 2017/8/21
 Time: 23:25
 To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>Title</title>
</head>
<body>
<form action="StudentServlet" method="post">
  姓名:<input type="text" name="name"><br>
  年龄:<input type="text" name="age"><br>
  成绩:<input type="text" name="score"><br>
  <input type="submit" value="输入">
  <input type="reset" value="重置">
</form>
</body>
</html>

4。展示学生的信息的页面


<%--
 Created by IntelliJ IDEA.
 User: wq
 Date: 2017/8/21
 Time: 23:25
 To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
  <title>Title</title>
</head>
<body>
 <h1>姓名：${student.name}</h1>
 <h1>年龄：${student.age}</h1>
 <h1>成绩：${student.score}</h1>
</body>
</html>