使用反射拼接SQL语句 和 使用 反射 + 注解 拼接SQL语句

• 以下知识本人都是用 Maven工程 总结的

 1、使用反射拼接SQL语句 

package com.csdn.anno;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Field;
import java.util.Properties;
public class AnnotationTest {
    public static void main(String[] args) throws ClassNotFoundException, IOException {
//        String sql = "select name,age,gender,city,score from student";
//        StringBuilder sql = new StringBuilder("select XXX,XXX,XXX");
        StringBuilder sql = new StringBuilder("select ");

        //通过 类加载器 读取文件
        InputStream inputStream = AnnotationTest.class.getClassLoader().getResourceAsStream("bean.properties");
        System.out.println(inputStream);//java.io.BufferedInputStream@7cca494b
        //读取properties配置文件，获取到配置文件里指定的类名
        Properties prop = new Properties();
        prop.load(AnnotationTest.class.getClassLoader().getResourceAsStream("bean.properties"));
        String className = (String) prop.get("className");
        //使用反射通过类名加载类
        Class clz = Class.forName(className);
        String tableName = clz.getSimpleName().toLowerCase();

        Field[] fields = clz.getDeclaredFields();

        for (int i = 0; i < fields.length; i++) {
            //遍历字段，获取字段名，添加到SQL语句
            String name = fields[i].getName();
            sql.append(name);
            if (i!= fields.length-1) {
                sql.append(",");
            }
        }

        sql.append(" from ").append(tableName);

        System.out.println(sql);//select name,age,gender,city,score from student

    }
}
class Student {
    private String name;
    private int age;
    private String gender;
    private String city;
    private String score;
}

className=com.csdn.anno.Student

2、使用 反射 + 注解 拼接SQL语句 

package com.csdn.anno;
import java.io.IOException;
import java.io.InputStream;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.Field;
import java.util.Properties;
public class AnnotationTest {
    public static void main(String[] args) throws ClassNotFoundException, IOException {
//        String sql = "select name,age,gender,city,score from student";
//        StringBuilder sql = new StringBuilder("select XXX,XXX,XXX");
        StringBuilder sql = new StringBuilder("select ");

        //通过 类加载器 读取文件
        InputStream inputStream = AnnotationTest.class.getClassLoader().getResourceAsStream("bean.properties");
        System.out.println(inputStream);//java.io.BufferedInputStream@7cca494b
        //读取properties配置文件，获取到配置文件里指定的类名
        Properties prop = new Properties();
        prop.load(AnnotationTest.class.getClassLoader().getResourceAsStream("bean.properties"));
        String className = (String) prop.get("className");
        //使用反射通过类名加载类
        Class clz = Class.forName(className);
        Table tableAnnotation = clz.getAnnotation(Table.class);  //获取到类上的注解
        String tableName = tableAnnotation != null ? tableAnnotation.value() : clz.getSimpleName().toLowerCase();

        //使用反射获取类里的字段
        Field[] fields = clz.getDeclaredFields();

        for (int i = 0; i < fields.length; i++) {
            //获取字段上的注解
            Column columnAnnotation = fields[i].getAnnotation(Column.class);

            //遍历字段，获取字段名，添加到SQL语句
            String name = columnAnnotation != null ? columnAnnotation.value() : fields[i].getName();
            sql.append(name);
            if (i != fields.length - 1) {
                sql.append(",");
            }
        }

        sql.append(" from ").append(tableName);

        System.out.println(sql);//select name,age,sex,city,score from t_student

    }
}
@Table("t_student")
class Student {

    private String name;
    private int age;
    @Column("sex")
    private String gender;
    private String city;
    private String score;
}
@Retention(RetentionPolicy.RUNTIME)
@interface Table {
    String value();
}

@Retention(RetentionPolicy.RUNTIME)
@interface Column {
    String value();
}