一探Spring中BeanUtils的copyProperties方法

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; } //获取目标对象的各属性信息 PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable); List<String> ignoreList = ignoreProperties != null ? Arrays.asList(ignoreProperties) : null; PropertyDescriptor[] var7 = targetPds; int var8 = targetPds.length; //遍历各属性 for(int var9 = 0; var9 < var8; ++var9) { PropertyDescriptor targetPd = var7[var9]; //获取目标对象该属性的写方法，即set方法 Method writeMethod = targetPd.getWriteMethod(); //判断该属性是否在不被copy的属性集合中 if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) { //根据目标对象的属性名称，获取源对象的该属性信息 PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName()); if (sourcePd != null) { //获取源对象的该属性的读方法，即get方法 Method readMethod = sourcePd.getReadMethod(); //判断目标对象的set方法所需的参数类型和源对象get方法的返回类型是否一致 if (readMethod != null && ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) { try { //如果源对象的get方法不包含public修饰符，将该方法修改为可以通过反射外部访问 if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) { readMethod.setAccessible(true); } //通过反射获取源对象该属性的值 Object value = readMethod.invoke(source); //如果目标对象的set方法不包含public修饰符，将该方法修改为可以通过反射外部访问 if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) { writeMethod.setAccessible(true); } //通过反射将值写入目标对象 writeMethod.invoke(target, value); } catch (Throwable var15) { throw new FatalBeanException("Could not copy property '" + targetPd.getName() + "' from source to target", var15); } } } } } }

通过copyProperties方法的源代码可以看出，实现此功能有三个必须条件： 1.需要复制的属性名要相同; 2.对于要复制的属性，源对象必须有get方法，目标对象必须有set方法; 3.目标对象的set方法所需的参数类型和源对象get方法的返回类型保持一致。

下面贴上测试类和测试代码：

被复制的类

public class CopyTest1 { private String outStr; private CopyTest1.Inner inner; private List<Integer> num; public static class Inner { public String inStr; } public String getOutStr() { return outStr; } public void setOutStr(String outStr) { this.outStr = outStr; } public Inner getInner() { return inner; } public void setInner(Inner inner) { this.inner = inner; } public List<Integer> getNum() { return num; } public void setNum(List<Integer> num) { this.num = num; } @Override public String toString() { return "CopyTest1{" + "outStr='" + outStr + '\'' + ", inner=" + inner + ", num=" + num + '}'; }

目标类

public class CopyTest2 { private String outStr; private CopyTest2.Inner inner; private List<String> num; public static class Inner { public String inStr; } public String getOutStr() { return outStr; } public void setOutStr(String outStr) { this.outStr = outStr; } public Inner getInner() { return inner; } public void setInner(Inner inner) { this.inner = inner; } public List<String> getNum() { return num; } public void setNum(List<String> num) { this.num = num; } @Override public String toString() { return "CopyTest2{" + "outStr='" + outStr + '\'' + ", inner=" + inner + ", num=" + num + '}'; } }

测试方法

public static void main(String[] args) { CopyTest1 test1 = new CopyTest1(); test1.setOutStr("hahahaha"); List<Integer> num = new ArrayList(); num.add(1); test1.setNum(num); CopyTest1.Inner inner = new CopyTest1.Inner(); inner.inStr = "hohohoho"; test1.setInner(inner); System.out.println(test1.toString()); CopyTest2 test2 = new CopyTest2(); BeanUtils.copyProperties(test1, test2); System.out.println(test2.toString()); }

从debug的效果看出属于两个类中的内部类，即使类名和属性名都相同相同，仍然不会复制，因为目标对象的set方法所需的参数类型和源对象get方法的返回类型是不一致，违反了条件3。因此，内部类需要单独使用copyProperties方法，复制一遍属性。

源对象中的list泛型为Integer，而目标对象中list的泛型为String，但是泛型只是编译期起约束作用，运行期可以看出set的参数类型和get的返回类型都是java.util.List，并无约束，因此也可以实现复制。

本文参考：www.jianshu.com/p/357b55852efc