【JAVA】实现注解拼接SQL+字段进行排序

package com.example.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface DataBaseTable {
public String tableName();
}

package com.example.annotation;

@DataBaseTable(tableName = "CustomTable")
public class CustomModel {
@ColumnsName(fieldName = "userId",number = 1)
public String mImUserId;

@ColumnsName(fieldName = "UserCustomList",number = 3)
public byte[] mUserCustomList;

@ColumnsName(fieldName = "datatype",number = 2)
public int mType;
}

package com.example.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ColumnsName {
String fieldName() default "";
int number() default 0;
}

package com.example.annotation;

import java.util.Comparator;

public class ColumnsComparator implements Comparator<ColumnsName>{

@Override
public int compare(ColumnsName c1, ColumnsName c2) {
if(c1.number() > c2.number()){
return 1;
}
if(c1.number() <= c2.number()){
return -1;
}
return 0;
}

}

package com.example.annotation;

import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class AnnotationTest {

/**
* 运行注解，拼出sql
*
* @param args
* @throws Exception
*/
public static void main(String[] args) throws Exception {
Field[] fields = CustomModel.class.getFields();
DataBaseTable tableModel = (DataBaseTable) CustomModel.class
.getAnnotation(DataBaseTable.class);
String tableName = tableModel.tableName();
List<ColumnsName> list = new ArrayList<ColumnsName>(fields.length);
String sql = "CREATE TABLE IF NOT EXISTS " + tableName + "(";
for (int i = 0; i < fields.length; i++) {
ColumnsName tabFeild = fields[i].getAnnotation(ColumnsName.class);
list.add(tabFeild);
if (tabFeild != null) {
if (i == 0) {
sql = sql + tabFeild.fieldName() + " "
+ getColumnType(fields[i].getType());
} else {
sql = sql + " ," + tabFeild.fieldName() + " "
+ getColumnType(fields[i].getType());
}
}
}
sql = sql + ");";
System.out.println(sql);
//对反射进行排序
Collections.sort(list, new ColumnsComparator());
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i).number() + "\t" + list.get(i).fieldName() );
}
}

/**
* 得到type
*
* @param type
* @return
*/
public static String getColumnType(Type type) {
String colums = "TEXT";
if (type == Long.class || (type == Long.TYPE)) {

} else if (Integer.class == type || (type == Integer.TYPE)) {
colums = "INTEGER";
} else if (type == String.class) {

} else if (type == byte[].class) {
colums = "BLOB";
}

return colums;
}

}