Java反射实战

怼烎@ 2022-06-03 01:29 156阅读 0赞

### 背景  ###

使用spring-ldap操作LDAP，完成**LdapTemplate**设置后，进行多条件查询，因为需求是能够多条件查询，所以在使用**ldapTemplate**.search系列方法时，着重考虑了下面的重载实现，第二个参数直接写过滤条件，只要按过滤语法书写即可，胜任各种复杂查询。

但是这个查询的，不能使用spring-ldap的ODM，不能把LDAP返回的查询结果，直接转成POJO；也就是需要把Attributes attributes转成我需要的LdapUser实体对象。

LdapUser.java如下：

import lombok.Getter;
    import lombok.Setter;
    import org.springframework.ldap.odm.annotations.Attribute;
    import org.springframework.ldap.odm.annotations.Entry;
    import org.springframework.ldap.odm.annotations.Id;
    import javax.naming.Name;
    
    @Setter
    @Getter
    @Entry(objectClasses = { "inetOrgPerson" ,"top","person" },base="ou=People")   // ou=Internal,   (只指定People，可按uid查询单个人员)
    public class LdapUser extends BaseDTO  {
    
        @Id
        protected Name dn;
    
        @Attribute(name = "uid")
        protected String uid;
    
        @Attribute(name = "smart-type")
        protected String userType;
    
        @Attribute(name = "mail")
        protected String mail;
    
        @Attribute(name = "mobile")
        protected String mobile;
    
        @Attribute(name = "departmentNumber")
        protected String deptId;
    
        @Attribute(name = "departmentName")
        protected String deptName;
        // ...
        }
    }

这个POJO使用了spring-ldap 的ODM注解，类和属性分别使用了@Entry和@Attribute(name = **"uid"**)，其中@Attribute 中的name则标识LDAP查询返回的Attributes 中的一个属性的名称。

### 下面要做的反射任务 ###

就是读取到POJO 这个LdapUser实体类中所有有带Attribute的属性，拿取到name后，从查询返回结果的Attributes 中遍历拿到对应name的 值，利用反射，给bean设置属性值。实现如下：

List<LdapUser> users = ldapTemplate.search("ou=People", "(&(objectClass=person)(smart-type=E1))", new AttributesMapper<LdapUser>() {
                @Override
                public LdapUser mapFromAttributes(Attributes attributes) throws NamingException {
                    LdapUser bean = null;
                    if (LdapUser.class.isAnnotationPresent(Entry.class)) {//是否加@Entry
                        try {
                            bean = LdapUser.class.newInstance();
                        } catch (Exception e) {
                            throw new RuntimeException("反射创建PIJO[<T extends BaseDTO>]实例对象失败",e);
                        }
    
                        Field[] fields = LdapUser.class.getDeclaredFields();//拿到bean对应的属性
                        for (Field field : fields) {//遍历POJO 所有属性
                            boolean fieldHasAnno = field.isAnnotationPresent(Attribute.class);//类属性上是否加@Attribute(name = "smart-type")
                            if (fieldHasAnno) {
                                Attribute fieldAnno = field.getAnnotation(Attribute.class);
                                String name = fieldAnno.name();//注解的name值,如smart-type
                                for (NamingEnumeration attrEnumeration = attributes.getAll(); attrEnumeration.hasMore(); ) {
                                    javax.naming.directory.Attribute attr = (javax.naming.directory.Attribute) attrEnumeration.next();
                                    String ldapAttr = attr.getID();
                                    if (ldapAttr.equals(name)) {
                                        String ldapValue = attr.get().toString();
                                        setProperty(bean, field.getName(), ldapValue);//反射：给bean设置属性值
                                    } else {
                                        continue;
                                    }
                                }
                            }
                        }
                    } else {
                        throw new RuntimeException("PIJO[<T extends BaseDTO>]需使用@Entry注解");
                    }
                    return bean;
                }
            });
    
    
        /**
         * 反射：给bean设置属性值
         *
         * @param bean
         * @param name
         * @param value
         */
        private void setProperty(Object bean, String name, Object value) {
            String setterName = "set" + StringUtils.capitalize(name);
            Method setter;
            try {
                setter = bean.getClass().getMethod(setterName, value.getClass());
                setter.invoke(bean, value);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }

因为考虑到通用性，就把这一部分反射的工作抽象出来，用泛型替换具体类型，

实现了一个通用的转化ConvertAttributesMapper

import org.apache.commons.lang3.StringUtils;
    import org.springframework.ldap.core.AttributesMapper;
    import org.springframework.ldap.odm.annotations.Attribute;
    import org.springframework.ldap.odm.annotations.Entry;
    
    import javax.naming.NamingEnumeration;
    import javax.naming.NamingException;
    import javax.naming.directory.Attributes;
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    
    /**
     * 实现Attributes 转成POJO
     */
    public class ConvertAttributesMapper<T extends BaseDTO> implements AttributesMapper {
    
        Class<T> clazz;
    
        public ConvertAttributesMapper(Class<T> clazz) {
            this.clazz = clazz;
        }
    
        @Override
        public T mapFromAttributes(Attributes attributes) throws NamingException {
            T bean = null;
            if (clazz.isAnnotationPresent(Entry.class)) {//是否加@Entry
                try {
                    bean = clazz.newInstance();
                } catch (Exception e) {
                    throw new RuntimeException("反射创建PIJO[<T extends BaseDTO>]实例对象失败",e);
                }
    
                Field[] fields = clazz.getDeclaredFields();//拿到bean对应的属性
                for (Field field : fields) {//遍历POJO 所有属性
                    boolean fieldHasAnno = field.isAnnotationPresent(Attribute.class);//类属性上是否加@Attribute(name = "smart-type")
                    if (fieldHasAnno) {
                        Attribute fieldAnno = field.getAnnotation(Attribute.class);
                        String name = fieldAnno.name();//注解的name值,如smart-type
                        for (NamingEnumeration attrEnumeration = attributes.getAll(); attrEnumeration.hasMore(); ) {
                            javax.naming.directory.Attribute attr = (javax.naming.directory.Attribute) attrEnumeration.next();
                            String ldapAttr = attr.getID();
                            if (ldapAttr.equals(name)) {
                                String ldapValue = attr.get().toString();
                                setProperty(bean, field.getName(), ldapValue);//反射：给bean设置属性值
                            } else {
                                continue;
                            }
                        }
                    }
                }
            } else {
                throw new RuntimeException("PIJO[<T extends BaseDTO>]需使用@Entry注解");
            }
            return bean;
        }
    
        /**
         * 反射：给bean设置属性值
         *
         * @param bean
         * @param name
         * @param value
         */
        private void setProperty(Object bean, String name, Object value) {
            String setterName = "set" + StringUtils.capitalize(name);
            Method setter;
            try {
                setter = bean.getClass().getMethod(setterName, value.getClass());
                setter.invoke(bean, value);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
    }
    
    //使用样例
    AttributesMapper attributesMapper = new ConvertAttributesMapper<LdapUser>(LdapUser.class);
    List<LdapUser> users = ldapTemplate.search("ou=People", "(&(objectClass=person)(smart-type=E1))", attributesMapper);

ps:BaseDTO是一个空的抽象类。