【Java 代码实例 14】BeanUtils用法详解，附源码分析

一、org.apache.commons.beanutils.BeanUtils简介

BeanUtils是Apache Commons组件的成员之一，主要用于简化JavaBean封装数据的操作。​
简化反射封装参数的步骤，给对象封装参数，好处是BeanUtils给对象封装参数的时候会进行类型自动转换。

二、使用的前置条件

1. 类//必须使用public修饰
2. 提供无参数的构造器
3. 提供getter和setter方法访问属性

三、添加pom

<dependency>
     <groupId>commons-beanutils</groupId>
     <artifactId>commons-beanutils</artifactId>
     <version>1.9.4</version>
</dependency>

四、org.apache.commons.beanutils.BeanUtils代码实例

1、为属性赋值

private static void setUserProperty() throws Exception {
    Worker worker = new Worker();

    BeanUtils.setProperty(worker, "id", "1");

    BeanUtils.setProperty(worker, "name", "哪吒");

    BeanUtils.setProperty(worker, "age", "28");

    System.out.println("id:"+ BeanUtils.getProperty(worker, "id"));

    System.out.println(worker);
}

2、拷贝对象，为对象赋值

private static void cloneBean() throws Exception {
    Worker worker1 = new Worker(3,"哪吒",18);
    // 拷贝对象
    Object object = BeanUtils.cloneBean(worker1);
    Worker worker2 = (Worker)object;
    System.out.println(worker2);//Worker{id=3, name='哪吒', age=18}
    System.out.println("worker1==worker2 : "+(worker1==worker2));//false

    // 拷贝对象属性
    Worker worker3 = new Worker();
    BeanUtils.copyProperties(worker3,worker1);
    System.out.println(worker3);//Worker{id=3, name='哪吒', age=18}
    System.out.println("worker1==worker3 : "+(worker1==worker3));//false

    // 为属性赋值
    Worker worker4 = new Worker();
    BeanUtils.copyProperty(worker4,"age",30);
    System.out.println(worker4);//Worker{id=0, name='null', age=30}
}

3、map转bean

private static void mapToBean() throws Exception {
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("id",2);
    map.put("name","哪吒");
    map.put("age",29);
    Worker user = new Worker();
    BeanUtils.populate(user,map);
    System.out.println(user);
}

4、bean转map

private static void beanToMap() throws Exception {
    Worker worker = new Worker(4,"哪吒编程",18);
    Map<String, String> map = BeanUtils.describe(worker);
    System.out.println(map);//{name=哪吒, id=4, age=18}

    // 为什么返回值是一个数组呢？
    String[] names = BeanUtils.getArrayProperty(worker, "name");
    System.out.println(names[0]);
}

五、Apache的BeanUtils与Spring的BeanUtils

默认情况下，使用org.apache.commons.beanutils.BeanUtils对复杂对象是进行的浅拷贝，但是由于Apache下的BeanUtils对象拷贝性能太差，不建议使用，这在阿里巴巴Java开发规约插件上也明确指出：

Ali-Check | 避免用Apache Beanutils进行属性的copy。

到这里你可能会疑惑，为什么会出现拷贝性能差的情况呢？

因为在对对象进行拷贝的时候添加很多的校验，比如像类型转换，甚至还校验了对象所属类的访问权限，可以说校验是相当的复杂，这也就是造成性能差的根本原因，我们看下它的具体代码实现：

public void copyProperties(final Object dest, final Object orig)
        throws IllegalAccessException, InvocationTargetException {

        // Validate existence of the specified beans
        if (dest == null) {
            throw new IllegalArgumentException
                    ("No destination bean specified");
        }
        if (orig == null) {
            throw new IllegalArgumentException("No origin bean specified");
        }
        if (log.isDebugEnabled()) {
            log.debug("BeanUtils.copyProperties(" + dest + ", " +
                      orig + ")");
        }

        // Copy the properties, converting as necessary
        if (orig instanceof DynaBean) {
            final DynaProperty[] origDescriptors =
                ((DynaBean) orig).getDynaClass().getDynaProperties();
            for (DynaProperty origDescriptor : origDescriptors) {
                final String name = origDescriptor.getName();
                // Need to check isReadable() for WrapDynaBean
                // (see Jira issue# BEANUTILS-61)
                if (getPropertyUtils().isReadable(orig, name) &&
                    getPropertyUtils().isWriteable(dest, name)) {
                    final Object value = ((DynaBean) orig).get(name);
                    copyProperty(dest, name, value);
                }
            }
        } else if (orig instanceof Map) {
            @SuppressWarnings("unchecked")
            final
            // Map properties are always of type <String, Object>
            Map<String, Object> propMap = (Map<String, Object>) orig;
            for (final Map.Entry<String, Object> entry : propMap.entrySet()) {
                final String name = entry.getKey();
                if (getPropertyUtils().isWriteable(dest, name)) {
                    copyProperty(dest, name, entry.getValue());
                }
            }
        } else /* if (orig is a standard JavaBean) */ {
            final PropertyDescriptor[] origDescriptors =
                getPropertyUtils().getPropertyDescriptors(orig);
            for (PropertyDescriptor origDescriptor : origDescriptors) {
                final String name = origDescriptor.getName();
                if ("class".equals(name)) {
                    continue; // No point in trying to set an object's class
                }
                if (getPropertyUtils().isReadable(orig, name) &&
                    getPropertyUtils().isWriteable(dest, name)) {
                    try {
                        final Object value =
                            getPropertyUtils().getSimpleProperty(orig, name);
                        copyProperty(dest, name, value);
                    } catch (final NoSuchMethodException e) {
                        // Should not happen
                    }
                }
            }
        }
    }

而org.springframework.beans.BeanUtils是使用 copyProperties方法进行拷贝，不过实现的方式相对于前者要来得简单得多了，可以说是非常的简单，就是根据两个对象属性的名字进行匹配，做简单的 get/set，仅检查属性的可访问性。具体实现如下：

private static void copyProperties(Object source, Object target, @Nullable Class<?> editable,
			@Nullable String... ignoreProperties) throws BeansException {

		Assert.notNull(source, "Source must not be null");
		Assert.notNull(target, "Target must not be null");

		Class<?> actualEditable = target.getClass();
		if (editable != null) {
			if (!editable.isInstance(target)) {
				throw new IllegalArgumentException("Target class [" + target.getClass().getName() +
						"] not assignable to Editable class [" + editable.getName() + "]");
			}
			actualEditable = editable;
		}
		PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable);
		List<String> ignoreList = (ignoreProperties != null ? Arrays.asList(ignoreProperties) : null);

		for (PropertyDescriptor targetPd : targetPds) {
			Method writeMethod = targetPd.getWriteMethod();
			if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
				PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName());
				if (sourcePd != null) {
					Method readMethod = sourcePd.getReadMethod();
					if (readMethod != null &&
							ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) {
						try {
							if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
								readMethod.setAccessible(true);
							}
							Object value = readMethod.invoke(source);
							if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) {
								writeMethod.setAccessible(true);
							}
							writeMethod.invoke(target, value);
						}
						catch (Throwable ex) {
							throw new FatalBeanException(
									"Could not copy property '" + targetPd.getName() + "' from source to target", ex);
						}
					}
				}
			}
		}
	}

从上面的实现源码可以看到：成员变量赋值是基于目标对象的成员列表，并且会跳过ignore以及在源对象中不存在的属性，所以这个方法是安全的，不会因为两个对象之间的结构差异导致错误，但是必须保证同名的两个成员变量类型相同。
以上简要的分析两种BeanUtils的具体实现以及性能相关的分析，得出结论：Apache下的BeanUtils由于各种繁琐的校验以及可访问性的校验等等，导致性能较差，故实际开发中不建议使用，可以使用 Spring的BeanUtils。

六、org.springframework.beans.BeanUtils代码实例

1、实例化

package com.guor.beanutil.spring;

import com.guor.beanutil.Worker;
import org.junit.Test;
import org.springframework.beans.BeanUtils;

public class SpringBeanUtilsTest {
    @Test
    public void testInstantiate() throws Exception{
        //通过无参数构造函数实例化
        Object obj = BeanUtils.instantiateClass(Worker.class);
        if(obj instanceof Worker) {
            System.out.println(((Worker) obj).getNezha());//哪吒
        }

        //通过有参数构造函数实例化
        Object obj2 = BeanUtils.instantiateClass(Worker.class.getDeclaredConstructor(String.class), "哪吒编程");
        if(obj2 instanceof Worker) {
            System.out.println(((Worker) obj2).getNezha());//哪吒编程
        }
    }
}

2、查找方法

（1）无参调用

@Test
public void testFindDeclaredMethod() throws Exception {
    Worker worker = new Worker();
    worker.setId(8);
    worker.setName("哪吒");

    Method method = BeanUtils.findDeclaredMethod(Worker.class, "getName");
    Object name = method.invoke(worker);
    System.out.println(name);//哪吒
}

（2）有参调用

@Test
public void testPropertyDescriptor2() throws Exception {
    Worker worker = new Worker();
    worker.setId(10);
    worker.setName("哪吒");

    Method method = BeanUtils.findMethod(Worker.class, "sayMsg",String.class,String.class);
    method.invoke(worker,"哪吒","我很帅");//哪吒 say :我很帅
}

（3）如果找不到方法

3、查找属性

@Test
public void testPropertyDescriptor() throws Exception {
    Worker worker = new Worker();
    worker.setId(10);
    worker.setName("哪吒");

    //获取属性
    PropertyDescriptor pd = BeanUtils.getPropertyDescriptor(Worker.class, "name");

    //获取属性的get方法
    Method getMethod = pd.getReadMethod();
    Object name = getMethod.invoke(worker);
    System.out.println(name);//哪吒

    //获取属性的get方法
    Method setMethod = pd.getWriteMethod();
    setMethod.invoke(worker, "哪吒编程");
    System.out.println(worker.getName());//哪吒编程
}

七、更多的Java代码实例

【Java 代码实例 4】javacompiler编译多java文件
【Java 代码实例 6】FileUtils、StringUtil、CollectionUtils、ArrayUtils（附代码示例）
【Java 代码实例 7】jsoup解析html
【Java 代码实例 8】qrcode生成二维码
【Java 代码实例 9】Java通过Process执行C# exe程序
【Java 代码实例 13】Java操作pdf的工具类itext

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