注解:java 自定义注解应用实例
2018-01-29 22:47
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注解:java 自定义注解应用实例
本例子旨在使用自定义注解为实体打上标记,为自动生成 sql 提供依据,模拟 hibernate 的注解,至于注解的原理自己搜吧
1.定义 Table 注解
[java] view
plain copy
package test;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Inherited
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Table {
String value() default "";
}
2.定义 Column 注解
[java] view
plain copy
package test;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Inherited
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Column {
String value() default "";
}
3.定义使用注解的实体
[java] view
plain copy
package test;
@Table("tb_test")
public class TestDto {
@Deprecated
private String tt;
@Column("_id")
private String id;
@Column("username")
private String name;
public TestDto(String id, String name) {
super();
this.id = id;
this.name = name;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
4.测试注解
[java] view
plain copy
package test;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Test {
public static void main(String[] args) {
TestDto testDto = new TestDto("123", "34");
TestDto testDto1 = new TestDto("123", "test1");
TestDto testDto2 = new TestDto("", "test1,test2,test3,test4");
String sql = assembleSqlFromObj(testDto);
String sql1 = assembleSqlFromObj(testDto1);
String sql2 = assembleSqlFromObj(testDto2);
System.out.println(sql);
System.out.println(sql1);
System.out.println(sql2);
}
/**
* 通过注解来组装查询条件,生成查询语句
*
* @param obj
* @return
*/
public static String assembleSqlFromObj(Object obj) {
Table table = obj.getClass().getAnnotation(Table.class);
StringBuffer sbSql = new StringBuffer();
String tableName = table.value();
sbSql.append("select * from " + tableName + " where 1=1 ");
Field[] fileds = obj.getClass().getDeclaredFields();
for (Field f : fileds) {
String fieldName = f.getName();
String methodName = "get" + fieldName.substring(0, 1).toUpperCase()
+ fieldName.substring(1);
try {
Column column = f.getAnnotation(Column.class);
if (column != null) {
Method method = obj.getClass().getMethod(methodName);
String value = (String) method.invoke(obj);
if (value != null && !value.equals("")) {
if (!isNum(column.value()) && !isNum(value)) {
// 判断参数是不是 in 类型参数 1,2,3
if (value.contains(",")) {
sbSql.append(" and " + column.value() + " in (" + value + ") ");
} else {
sbSql.append(" and " + column.value() + " like '%" + value + "%' ");
}
} else {
sbSql.append(" and " + column.value() + "=" + value + " ");
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
return sbSql.toString();
}
/**
* 检查给定的值是不是 id 类型 1.检查字段名称 2.检查字段值
*
* @param target
* @return
*/
public static boolean isNum(String target) {
boolean isNum = false;
if (target.toLowerCase().contains("id")) {
isNum = true;
}
if (target.matches("\\d+")) {
isNum = true;
}
return isNum;
}
}
测试结果:
select * from tb_test where 1=1 and _id=123 and username=34
select * from tb_test where 1=1 and _id=123 and username like '%test1%'
select * from tb_test where 1=1 and username in (test1,test2,test3,test4)
转载自 十年磨一剑_卧薪尝胆 https://www.cnblogs.com/keyi/p/6797044.html
本例子旨在使用自定义注解为实体打上标记,为自动生成 sql 提供依据,模拟 hibernate 的注解,至于注解的原理自己搜吧
1.定义 Table 注解
[java] view
plain copy
package test;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Inherited
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Table {
String value() default "";
}
2.定义 Column 注解
[java] view
plain copy
package test;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Inherited
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Column {
String value() default "";
}
3.定义使用注解的实体
[java] view
plain copy
package test;
@Table("tb_test")
public class TestDto {
@Deprecated
private String tt;
@Column("_id")
private String id;
@Column("username")
private String name;
public TestDto(String id, String name) {
super();
this.id = id;
this.name = name;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
4.测试注解
[java] view
plain copy
package test;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Test {
public static void main(String[] args) {
TestDto testDto = new TestDto("123", "34");
TestDto testDto1 = new TestDto("123", "test1");
TestDto testDto2 = new TestDto("", "test1,test2,test3,test4");
String sql = assembleSqlFromObj(testDto);
String sql1 = assembleSqlFromObj(testDto1);
String sql2 = assembleSqlFromObj(testDto2);
System.out.println(sql);
System.out.println(sql1);
System.out.println(sql2);
}
/**
* 通过注解来组装查询条件,生成查询语句
*
* @param obj
* @return
*/
public static String assembleSqlFromObj(Object obj) {
Table table = obj.getClass().getAnnotation(Table.class);
StringBuffer sbSql = new StringBuffer();
String tableName = table.value();
sbSql.append("select * from " + tableName + " where 1=1 ");
Field[] fileds = obj.getClass().getDeclaredFields();
for (Field f : fileds) {
String fieldName = f.getName();
String methodName = "get" + fieldName.substring(0, 1).toUpperCase()
+ fieldName.substring(1);
try {
Column column = f.getAnnotation(Column.class);
if (column != null) {
Method method = obj.getClass().getMethod(methodName);
String value = (String) method.invoke(obj);
if (value != null && !value.equals("")) {
if (!isNum(column.value()) && !isNum(value)) {
// 判断参数是不是 in 类型参数 1,2,3
if (value.contains(",")) {
sbSql.append(" and " + column.value() + " in (" + value + ") ");
} else {
sbSql.append(" and " + column.value() + " like '%" + value + "%' ");
}
} else {
sbSql.append(" and " + column.value() + "=" + value + " ");
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
return sbSql.toString();
}
/**
* 检查给定的值是不是 id 类型 1.检查字段名称 2.检查字段值
*
* @param target
* @return
*/
public static boolean isNum(String target) {
boolean isNum = false;
if (target.toLowerCase().contains("id")) {
isNum = true;
}
if (target.matches("\\d+")) {
isNum = true;
}
return isNum;
}
}
测试结果:
select * from tb_test where 1=1 and _id=123 and username=34
select * from tb_test where 1=1 and _id=123 and username like '%test1%'
select * from tb_test where 1=1 and username in (test1,test2,test3,test4)
转载自 十年磨一剑_卧薪尝胆 https://www.cnblogs.com/keyi/p/6797044.html
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