Apache BeanUtils工具介绍

beanutils，顾名思义，是java bean的一个工具类，可以帮助我们方便的读取(get)和设置(set)bean属性值、动态定义和访问bean属性；细心的话，会发现其实JDK已经提供了一个java.beans包，同样可以实现以上功能，只不过使用起来比较麻烦，所以诞生了apache commons beanutils；看源码就知道，其实apache commons beanutils就是基于jdk的java.beans包实现的。

maven：

commons-chain

commons-chain

1.2

commons-chain包主要有以下三个工具类：BeanUtils、PropertyUtils、ConvertUtils

1、设置、访问Bean的属性

1.1）javabean一般有以下几个特性：

1）类必须是public访问权限，且需要有一个public的无参构造方法，之所以这样主要是方便利用Java的反射动态创建对象实例：

Class beanClass = Class.forName(className);

Object beanInstance = beanClass.newInstance();

2）由于javabean的构造方法是无参的，所以我们的bean的行为配置（即设置bean的属性值）不能在构造方法完成，必须通过set方法来设置属性值。这里的setter方法会按一定的约定来命名，如setHireDate、setName。。。

3）读取和设置bean属性值的命名约定，即getter方法和setter方法，不过这里需要特别注意boolean类型的约定，如下示例：

private String firstName;

private String lastName;

private Date hireDate;

private boolean isManager;

public String getFirstName();

public void setFirstName(String firstName);

public String getLastName();

public void setLastName(String lastName);

public Date getHireDate();

public void setHireDate(Date hireDate);

public boolean isManager();

public void setManager(boolean manager);

4）并不是必须为每个属性提供setter和getter方法，我们可以只定义一个属性的getter方法而不定义setter方法，这样的属性一般是只读属性；

1.2）实战

可以通过BeanUtils和PropertyUtils设置、获取Bean的属性。

1）PropertyUtils设置、获取属性：

基本数据类型：

PropertyUtils.getSimpleProperty(Object, String)PropertyUtils.setSimpleProperty(Object, String, Object)索引类型：

PropertyUtils.getIndexedProperty(Object, String)

PropertyUtils.getIndexedProperty(Object, String, int)PropertyUtils.setIndexedProperty(Object, String, Object)PropertyUtils.setIndexedProperty(Object, String, int, Object)Map类型：

PropertyUtils.getMappedProperty(Object, String)

PropertyUtils.getMappedProperty(Object, String, String)PropertyUtils.setMappedProperty(Object, String, Object)PropertyUtils.setMappedProperty(Object, String, String, Object)嵌套类型：

PropertyUtils.getNestedProperty(Object, String)PropertyUtils.setNestedProperty(Object, String, Object)通用类型：

PropertyUtils.getProperty(Object, String)PropertyUtils.setProperty(Object, String, Object)

示例：

//定义bean

@Data

@ToString

public class Course {

private String name;

private List codes;

private Map enrolledStudent = new HashMap<>();

}

@Data

@ToString

public class Student {

private String name;

}

//测试

Course course = new Course(); //该类必须是public的、且有默认构造方法

String name = "Computer Science";

List codes = Arrays.asList("CS", "CS01");

//Simple Property

PropertyUtils.setSimpleProperty(course, "name", name);

PropertyUtils.setSimpleProperty(course, "codes", codes);

System.out.println(course);

String nameV = (String)PropertyUtils.getSimpleProperty(course, "name");

System.out.println(nameV);

//Indexed Property

PropertyUtils.setIndexedProperty(course, "codes[1]", "CS02");

PropertyUtils.setIndexedProperty(course, "codes", 1, "CS03");

System.out.println(course);

String indexedProperty = (String)PropertyUtils.getIndexedProperty(course, "codes", 1);

String indexedProperty2 = (String)PropertyUtils.getIndexedProperty(course, "codes[1]");

System.out.println(indexedProperty + "," + indexedProperty2);

Student student = new Student();

String studentName = "Joe";

student.setName(studentName);

//Mapped Property

PropertyUtils.setMappedProperty(course, "enrolledStudent(ST-1)", student);

PropertyUtils.setMappedProperty(course, "enrolledStudent", "ST-1", student);

System.out.println(course);

Student mappedProperty = (Student)PropertyUtils.getMappedProperty(course, "enrolledStudent", "ST-1");

Student mappedProperty2 = (Student)PropertyUtils.getMappedProperty(course, "enrolledStudent(ST-1)");

System.out.println(mappedProperty + "," + mappedProperty2);

//Nested Property

PropertyUtils.setNestedProperty(course, "enrolledStudent(ST-1).name", "Joe_1");

String nameValue = (String) PropertyUtils.getNestedProperty(course, "enrolledStudent(ST-1).name");

//等价于 String name = course.getEnrolledStudent("ST-1").getName();

System.out.println(nameValue);

以上还可以使用下面的方式：

private static void test1_1() throws Exception {

Course course = new Course();

String name = "Computer Science";

List codes = Arrays.asList("CS", "CS01");

//Simple Property

PropertyUtils.setProperty(course, "name", name);

PropertyUtils.setProperty(course, "codes", codes);

System.out.println(course);

String nameV = (String)PropertyUtils.getProperty(course, "name");

System.out.println(nameV);

//Indexed Property

PropertyUtils.setProperty(course, "codes[1]", "CS02");

System.out.println(course);

Student student = new Student();

String studentName = "Joe";

student.setName(studentName);

//Mapped Property

PropertyUtils.setProperty(course, "enrolledStudent(ST-1)", student);

System.out.println(course);

//Nested Property

PropertyUtils.setProperty(course, "enrolledStudent(ST-1).name", "Joe_1");

String nameValue = (String) PropertyUtils.getProperty(course, "enrolledStudent(ST-1).name");

System.out.println(nameValue);

}

2）BeanUtils设置、获取属性：

BeanUtils只有以下两个方法来设置、获取属性

BeanUtils.getProperty(Object, String)BeanUtils.setProperty(Object, String, Object)

 示例：

private static void test1_2() throws Exception {

Course course = new Course();

String name = "Computer Science";

List codes = Arrays.asList("CS", "CS01");

//Simple Property

BeanUtils.setProperty(course, "name", name);

BeanUtils.setProperty(course, "codes", codes);

System.out.println(course);

String nameV = (String)BeanUtils.getProperty(course, "name");

System.out.println(nameV);

//Indexed Property

BeanUtils.setProperty(course, "codes[1]", "CS02");

System.out.println(course);

Student student = new Student();

String studentName = "Joe";

student.setName(studentName);

//Mapped Property

BeanUtils.setProperty(course, "enrolledStudent(ST-1)", student);

System.out.println(course);

//Nested Property

BeanUtils.setProperty(course, "enrolledStudent(ST-1).name", "Joe_1");

String nameValue = (String) BeanUtils.getProperty(course, "enrolledStudent(ST-1).name");

System.out.println(nameValue);

}

2、拷贝Bean的属性

2.1）BeanUtils有一下两个方法：

populate：把Map里的键值对值拷贝到bean的属性值中；copyProperties：拷贝一个bean的属性到另外一个bean中，注意是浅拷贝

注意：populate和copyProperties的区别，对于Integer、Float、Boolean类型前者（populate）对于null值，在拷贝到Bean的属性后会变成默认值。

1）populate：

//bean定义

import java.util.Date;

import lombok.Data;

import lombok.NoArgsConstructor;

@Data

@NoArgsConstructor

public class Employee {

private Integer id;

private String name;

private Boolean isGood;

private Float score;

private Date createTime;

public Employee(Integer id, String name, Boolean isGood, Float score, Date createTime) {

this.id = id;

this.name = name;

this.isGood = isGood;

this.score = score;

this.createTime = createTime;

}

}

//测试

Map map = new HashMap<>(2);

map.put("id", null);

map.put("name", "employee1");

map.put("isGood", null);

map.put("createTime", new Date()); //如果是null，会报错

map.put("add", "add1");

// map > obj

Employee e = new Employee();

BeanUtils.populate(e, map);

System.out.println(e); //Employee(id=0, name=employee1, isGood=false, createTime=Tue Aug 15 10:42:14 CST 2023)

//支持类型转换

Map map = new HashMap<>(5);

map.put("id", "123");

map.put("name", 1.9);

map.put("isGood", "2");

map.put("score", null);

map.put("createTime", new Date());

map.put("add", "add1");

// map > obj

Employee e = new Employee();

BeanUtils.populate(e, map);

System.out.println(e); //Employee(id=123, name=1.9, isGood=false, score=1.0, createTime=Tue Aug 15 12:34:41 CST 2023)

说明：

对于Integer、Float、Boolean类型，如果是null，则转成bean的属性后会变成默认值（0，0.1，false）对于Date类型，如果是null或者其他类型，转成bean的时候会报错，需要使用ConvertUtils进行类型转换（见下面）支持类型转换：比如Integer和String之间

2）copyProperties：

有另外一个对象（类型和Employee不同）

@Data

public class Employee2 {

private Integer id;

private String name;

private String isGood;

private String score;

private String createTime;

private Float f1;

}

测试

private static void test2_1() throws Exception {

Employee ee = new Employee(null, "employee2", null, null, null);

Employee2 e1 = new Employee2();

BeanUtils.copyProperties(e1, ee);

System.out.println(e1); //Employee2(id=null, name=employee2, isGood=null, score=null, createTime=null, f1=null)

Employee ee2 = new Employee(1, "employee2", true, 4.3f, new Date());

Employee2 e2 = new Employee2();

BeanUtils.copyProperties(e2, ee2);

System.out.println(e2); //Employee2(id=1, name=employee2, isGood=true, score=4.3, createTime=Tue Aug 15 11:45:06 CST 2023, f1=null)

}

说明：

对于Integer、Float、Boolean、Date类型，如果是null，拷贝后也是null支持类型转换：两个bean只要属性名一样，类型可转换即可拷贝。比如Integer、Float、Boolean类型转成String

2.2）PropertyUtils进行属性拷贝：

1）和BeanUtils区别：

PropertyUtils只支持两个Bean之间的属性拷贝，不支持Map到Bean的PropertyUtils在两个Bean之间进行属性拷贝时，必须要保证名字和类型都一样才行，否则会报错。BeanUtils在进行属性拷贝时，名字一样，类型可转换即可。

Employee ee = new Employee(null, "employee2", null, null, null);

Employee2 e1 = new Employee2();

PropertyUtils.copyProperties(e1, ee);

System.out.println(e1); //Employee2(id=null, name=employee2, isGood=null, score=null, createTime=null, f1=null)

Employee ee2 = new Employee(1, "employee2", true, 4.3f, new Date());

Employee2 e2 = new Employee2();

PropertyUtils.copyProperties(e2, ee2);

System.out.println(e2); //报错

报错信息：

2）说明：

PropertyUtils不支持类型转换。对于null值，PropertyUtils拷贝后也是null

3、ConvertUtils自定义类型转换

1）DateConverter：

DateConverter继承DateTimeConverter，是beanutils包中自带的时间类型转换，包含了：

示例

DateConverter converter = new DateConverter();

converter.setPattern("yyyy-MM-dd");

ConvertUtils.register(converter, java.util.Date.class);

Map map = new HashMap<>(5);

map.put("id", 1);

map.put("name", "testConvertUtils");

map.put("isGood", false); //可以是Integer或String，1或"1" true 其他表示false,null表示false

map.put("score", 1.1f);

map.put("createTime", "2023-08-15");

map.put("add", "add1");

// map > obj

Employee e = new Employee();

BeanUtils.populate(e, map);

System.out.println(e); //Employee(id=1, name=testConvertUtils, isGood=false, score=1.1, createTime=Tue Aug 15 00:00:00 CST 2023)

2）自定义： 

ConvertUtils.register(new Converter() {

public Object convert(Class type, Object value) {

SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");

try {

return simpleDateFormat.parse(value.toString());

} catch (Exception e) {

e.printStackTrace();

}

return null;

}

}, Date.class);

Employee e1 = new Employee();

BeanUtils.setProperty(e1, "createTime", "2022-09-09");

System.out.println(e1.getCreateTime()); //Fri Sep 09 00:00:00 CST 2022

说明：对于setProperty，如果存在时间类型，需要自定义转换器。

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