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();
}
