利用反射及jdbc元数据实现通用的查询方法

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1.customer类：

package com.lanqiao.javatest;

import java.sql.Date;

public class Customer {
private int id;
private String name;
private String email;
private Date birth;

public Customer() {
super();
}

public Customer(int id, String name, String email, Date birth) {
super();
this.id = id;
this.name = name;
this.email = email;
this.birth = birth;
}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getEmail() {
return email;
}

public void setEmail(String email) {
this.email = email;
}

public Date getBirth() {
return birth;
}

public void setBirth(Date birth) {
this.birth = birth;
}

@Override
public String toString() {
return "Customer [id=" + id + ", name=" + name + ", email=" + email + ", birth=" + birth + "]";
}
}

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student类：

package com.lanqiao.javatest;

public class Student {

/*
* FlowID:int，流水号
* type:int ，英语四六级
* IDcard:varchar(18),身份证号码
* examcard：varchar（15），考试证号
* studentname:varchar（20），学生姓名
* localtion：varchar（20），区域
* grade：int，成绩
*/
private int flowId;
private int type;
private String idCard;
private String examCard;
private String studentName;
private String localtion;
private int grade;

public Student() {
super();
}

public Student(int flowId, int type, String idCard, String examCard, String studentName, String localtion,
int grade) {
super();
this.flowId = flowId;
this.type = type;
this.idCard = idCard;
this.examCard = examCard;
this.studentName = studentName;
this.localtion = localtion;
this.grade = grade;
}

public int getFlowId() {
return flowId;
}
public void setFlowId(int flowId) {
this.flowId = flowId;
}
public int getType() {
return type;
}
public void setType(int type) {
this.type = type;
}
public String getIdCard() {
return idCard;
}
public void setIdCard(String idCard) {
this.idCard = idCard;
}
public String getExamCard() {
return examCard;
}
public void setExamCard(String examCard) {
this.examCard = examCard;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public String getLocaltion() {
return localtion;
}
public void setLocaltion(String localtion) {
this.localtion = localtion;
}
public int getGrade() {
return grade;
}
public void setGrade(int grade) {
this.grade = grade;
}

@Override
public String toString() {
return "Person [flowId=" + flowId + ", type=" + type + ", idCard=" + idCard + ", examCard=" + examCard
+ ", studentName=" + studentName + ", localtion=" + localtion + ", grade=" + grade + "]";
}

}

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反射方法：

package com.lanqiao.javatest;

import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
* 反射的 Utils 函数集合
* 提供访问私有变量, 获取泛型类型 Class, 提取集合中元素属性等 Utils 函数
* @author Administrator
*
*/
public class ReflectionUtils {

/**
* 通过反射, 获得定义 Class 时声明的父类的泛型参数的类型
* 如: public EmployeeDao extends BaseDao<Employee, String>
* @param clazz
* @param index
* @return
*/
@SuppressWarnings("unchecked")
public static Class getSuperClassGenricType(Class clazz, int index){
Type genType = clazz.getGenericSuperclass();

if(!(genType instanceof ParameterizedType)){
return Object.class;
}

Type [] params = ((ParameterizedType)genType).getActualTypeArguments();

if(index >= params.length || index < 0){
return Object.class;
}

if(!(params[index] instanceof Class)){
return Object.class;
}

return (Class) params[index];
}

/**
* 通过反射, 获得 Class 定义中声明的父类的泛型参数类型
* 如: public EmployeeDao extends BaseDao<Employee, String>
* @param <T>
* @param clazz
* @return
*/
@SuppressWarnings("unchecked")
public static<T> Class<T> getSuperGenericType(Class clazz){
return getSuperClassGenricType(clazz, 0);
}

/**
* 循环向上转型, 获取对象的 DeclaredMethod
* @param object
* @param methodName
* @param parameterTypes
* @return
*/
public static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes){

for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){
try {
//superClass.getMethod(methodName, parameterTypes);
return superClass.getDeclaredMethod(methodName, parameterTypes);
} catch (NoSuchMethodException e) {
//Method 不在当前类定义, 继续向上转型
}
//..
}

return null;
}

/**
* 使 filed 变为可访问
* @param field
*/
public static void makeAccessible(Field field){
if(!Modifier.isPublic(field.getModifiers())){
field.setAccessible(true);
}
}

/**
* 循环向上转型, 获取对象的 DeclaredField
* @param object
* @param filedName
* @return
*/
public static Field getDeclaredField(Object object, String filedName){

for(Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass.getSuperclass()){
try {
return superClass.getDeclaredField(filedName);
} catch (NoSuchFieldException e) {
//Field 不在当前类定义, 继续向上转型
}
}
return null;
}

/**
* 直接调用对象方法, 而忽略修饰符(private, protected)
* @param object
* @param methodName
* @param parameterTypes
* @param parameters
* @return
* @throws InvocationTargetException
* @throws IllegalArgumentException
*/
public static Object invokeMethod(Object object, String methodName, Class<?> [] parameterTypes,
Object [] parameters) throws InvocationTargetException{

Method method = getDeclaredMethod(object, methodName, parameterTypes);

if(method == null){
throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]");
}

method.setAccessible(true);

try {
return method.invoke(object, parameters);
} catch(IllegalAccessException e) {
System.out.println("不可能抛出的异常");
}

return null;
}

/**
* 直接设置对象属性值, 忽略 private/protected 修饰符, 也不经过 setter
* @param object
* @param fieldName
* @param value
*/
public static void setFieldValue(Object object, String fieldName, Object value){
Field field = getDeclaredField(object, fieldName);

if (field == null)
throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");

makeAccessible(field);

try {
field.set(object, value);
} catch (IllegalAccessException e) {
System.out.println("不可能抛出的异常");
}
}

/**
* 直接读取对象的属性值, 忽略 private/protected 修饰符, 也不经过 getter
* @param object
* @param fieldName
* @return
*/
public static Object getFieldValue(Object object, String fieldName){
Field field = getDeclaredField(object, fieldName);

if (field == null)
throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");

makeAccessible(field);

Object result = null;

try {
result = field.get(object);
} catch (IllegalAccessException e) {
System.out.println("不可能抛出的异常");
}

return result;
}
}

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实现主方法：

package com.lanqiao.javatest;

import java.io.InputStream;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Properties;

import javax.management.ReflectionException;
import javax.swing.text.FieldView;

import org.junit.Test;

import com.mysql.jdbc.ResultSetMetaData;
import com.mysql.jdbc.Statement;

/*
* 建立一个统一的方法可以引用任何类的对象，实现数据库数据的处理
* 通过一个对象获取任何一个数据库数据
* */
public class TestPreparedStatement {

private static final Class<Customer> Customer = null;
private static final Class<Student> Student = null;

=================================================================================
//连接数据库方法
public static Connection getConnection() throws Exception{

//四连接数据必不可少的
String driverClass=null;
String jdbcUrl=null;
String user=null;
String password=null;

InputStream in=
TestPreparedStatement.class.getClassLoader().getResourceAsStream("jdbc.properties");
//其中getClass与TestConnection.classh互换使用
Properties properties=new Properties();
properties.load(in);

driverClass=properties.getProperty("driver");
jdbcUrl=properties.getProperty("jdbcUrl");
user=properties.getProperty("user");
password=properties.getProperty("password");

// System.out.println(driverClass+jdbcUrl+user+password);
Driver driver=(Driver)Class.forName(driverClass).newInstance();
Properties info=new Properties();
info.put("user", "root");
info.put("password", "lxn123");
Connection connection=driver.connect(jdbcUrl, info);
return connection;
}
//测试类
public static void testGetConn() throws Exception{
System.out.println(getConnection());
}

====================================================================================

关闭资源的方法

public void close(Connection connection,
PreparedStatement preparedStatement,ResultSet resultSet) throws Exception{
if (resultSet!=null) {
resultSet.close();
}
if (preparedStatement!=null) {
preparedStatement.close();
}
if (connection!=null) {
connection.close();
}
}

===========================================================================================
//student类获取数据
public Student getStudent(String sql,Object...args) throws Exception{
Student student=null;
Connection connection=null;
PreparedStatement preparedStatement=null;
ResultSet resultSet=null;

try {
connection=TestPreparedStatement.getConnection();
preparedStatement=connection.prepareStatement(sql);
for(int i=0;i<args.length;i++){
preparedStatement.setObject(i+1, args[i]);
}
resultSet=preparedStatement.executeQuery();
//resultset里面的nest()方法，把查询到的数据，student获取
if(resultSet.next()){
student=new Student();
student.setFlowId(resultSet.getInt(1));
student.setType(resultSet.getInt(2));
student.setIdCard(resultSet.getString(3));
student.setExamCard(resultSet.getString(4));
student.setStudentName(resultSet.getString(5));
student.setLocaltion(resultSet.getString(6));
student.setGrade(resultSet.getInt(7));
}
} catch (Exception e) {
e.printStackTrace();
}finally {
close(connection,preparedStatement,resultSet);
}

return student;

}

========================================================================================
//Customer类获取数据
public Customer getCustomer(String sql,Object...args) throws Exception{
Customer customer=null;
Connection connection=null;
PreparedStatement preparedStatement=null;
ResultSet resultSet=null;

try {
connection=TestPreparedStatement.getConnection();
preparedStatement=connection.prepareStatement(sql);
for(int i=0;i<args.length;i++){
preparedStatement.setObject(i+1, args[i]);
}
resultSet=preparedStatement.executeQuery();
//resultset里面的nest()方法，把查询到的数据，student获取
if(resultSet.next()){
customer=new Customer();
customer.setId(resultSet.getInt(1));
customer.setName(resultSet.getString(2));
customer.setEmail(resultSet.getString(3));
customer.setBirth(resultSet.getDate(4));
}
} catch (Exception e) {
e.printStackTrace();
}finally {
close(connection,preparedStatement,resultSet);
}

return customer;
}
=======================================================================================
//一个通用的方法的模板：可利用反射，实现数据库查询，插入值
public <T> T getT(Class <T> clazz,String sql,Object...args) throws Exception{
T entity=null;

Connection connection=null;
PreparedStatement preparedStatement=null;
ResultSet resultSet=null;

try {
connection=TestPreparedStatement.getConnection();
preparedStatement=connection.prepareStatement(sql);
for(int i=0;i<args.length;i++){
preparedStatement.setObject(i+1, args[i]);
}
resultSet=preparedStatement.executeQuery();

//得到ResultSetMetaDate对象,获取数据库中的列和列名
ResultSetMetaData rsmd=(ResultSetMetaData) resultSet.getMetaData();

//创建一个Map<String,Object>对象，键：sql查询列的别名；值：列的值；
Map<String, Object> values=new HashMap<String, Object>();

//处理结果集，利用ResultSetMetaDate的方法，填充对应的map的对象
while(resultSet.next()){
//方法getColumnCount()，是获取ResultSetMetaDate对象获取数据库属性的个数
for(int i=0;i<rsmd.getColumnCount();i++){
String columnLabel=rsmd.getColumnLabel(i+1);//获取属性，它是字符串
Object columnValues=resultSet.getObject(columnLabel);
// System.out.println(columnValues);
values.put(columnLabel, columnValues);
}
}

//map不为空，利用反射创建clazz的对象
if (values.size()>0) {
entity=clazz.newInstance();

//遍历map,利用反射class对应的对象的属性赋值
for (Map.Entry<String, Object> entry: values.entrySet()) {
String fieldName=entry.getKey();
Object fieldValues=entry.getValue();
System.out.println(fieldName+":"+fieldValues);
//反射获取属性，并修改 xxxx(entity,fieldName,fieldValues);
ReflectionUtils.setFieldValue(entity, fieldName, fieldValues);
}

}

} catch (Exception e) {
e.printStackTrace();
}finally {
close(connection,preparedStatement,resultSet);
}
return entity;
}
//测试getT()方法
@Test
public void testGetT() throws Exception{
String sql="select id,name,email,birth from customer where id=?";
Customer customer=getT(Customer.class,sql,2);
System.out.println(customer);

String sql1="SELECT flow_id flowId,type,id_card idCard,"
+ "exam_card examCard,student_name studentName ,"
+ "localtion,grade FROM test WHERE flow_id=?;";
Student student=getT(Student.class,sql1,2);
System.out.println(student);
}
=======================================================================================
//ResultSetMetaDate，是描述ResultSet的元数据对象，即从中可以获取到结果集中有多少列，列名是。。。。。
//用法：调用ResultSet的getMetaDate()方法，
//好用的方法：int getColumnCount(),sql语句中包含那些列
//String getColumnLabel(int column):获取指定列的别名，其中索引从1开始

public void testResultSetMetaDate() throws Exception{
Connection connection=null;
PreparedStatement preparedStatement=null;
ResultSet resultSet=null;

try {
String sql="SELECT flow_id flowid,type,id_card idcard,"
+ "exam_card examcard,student_name studentname ,"
+ "localtion,grade FROM test WHERE flow_id=?;";
connection=TestPreparedStatement.getConnection();
preparedStatement=connection.prepareStatement(sql);
preparedStatement.setInt(1, 2);
resultSet=preparedStatement.executeQuery();

Map<String, Object> values=new HashMap<String, Object>();

//1.得到ResultSetMetaDate对象,获取数据库中的列和列名
ResultSetMetaData rsmd= (ResultSetMetaData) resultSet.getMetaData();
while(resultSet.next()){
//2.{}打印每一列的列名
for(int i=0;i<rsmd.getColumnCount();i++){
String columnLabel=rsmd.getColumnLabel(i+1);//获取指定列的别名
Object columnValue=resultSet.getObject(columnLabel);//获取指定列的值

values.put(columnLabel, columnValue);

}
}
System.out.println(values);

//反射获取
Class clazz=Student.class;
Object obj=clazz.newInstance();
//强制for循环
for(Map.Entry<String, Object> entry: values.entrySet()){
String fieldName=entry.getKey();
Object fieldValues=entry.getValue();
System.out.println(fieldName+"："+fieldValues);
}

} catch (Exception e) {
e.printStackTrace();
}finally {
close(connection,preparedStatement,resultSet);
}
}

}

数据库图片：