Java反射实战

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。

List<LdapUser> users = ldapTemplate.search("ou=People", "(&(objectClass=person)(smart-type=E1))", new AttributesMapper<LdapUser>() {
    @Override
    public LdapUser mapFromAttributes(Attributes attributes) throws NamingException {
        
        return null;
    }
});

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；也就是需要自己把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。