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：

<dependency>
        <groupId>commons-chain</groupId>
        <artifactId>commons-chain</artifactId>
        <version>1.2</version>
</dependency>

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<String> codes;
    private Map<String, Student> 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<String> 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<String> 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<String> 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<String, Object> 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<String, Object> 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<String, Object> 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。