[JavaWeb基础] 029.OGNL表达式介绍

1.OGNL概述

OGNL，全称为Object-Graph Navigation Language，它是一个功能强大的表达式语言，用来获取和设置Java对象的属性，它旨在提供一个更高的更抽象的层次来对Java对象图进行导航。

OGNL表达式的基本单位是"导航链"，一般导航链由如下几个部分组成：

1. 属性名称（property）
2. 方法调用（method invoke）
3. 数组元素

所有的OGNL表达式都基于当前对象的上下文来完成求值运算，链的前面部分的结果将作为后面求值的上下文。例如：names[0].length()。

2.OGNL操作属性

public class OGNL1 {
	public static void main(String[] args) {
		/** 创建一个Person对象 **/
		Person person = new Person();
		person.setName("zhangsan");
		try {
			/** 从person对象中获取name属性的值  **/
			Object value = Ognl.getValue("name", person);
			System.out.println(value);
		} catch (OgnlException e) {
			e.printStackTrace();
		}
	}
}

/** model 实体类 **/
class Person {
	private String name;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}
}

3.OGNL访问context

public class OGNL1 {
	public static void main(String[] args) {
		/** 创建一个上下文Context对象，它是用保存多个对象一个环境 对象 **/
		Map<String, Object> context = new HashMap<String, Object>();

		Person person1 = new Person();
		person1.setName("zhangsan");

		Person person2 = new Person();
		person2.setName("lisi");

		Person person3 = new Person();
		person3.setName("wangwu");

		/* person4不放入到上下文环境中 */
		Person person4 = new Person();
		person4.setName("zhaoliu");

		/** 将person1、person2、person3添加到环境中（上下文中） **/
		context.put("person1", person1);
		context.put("person2", person2);
		context.put("person3", person3);

		try {
			/** 获取根对象的"name"属性值 **/
			/** 从根对象person2，直接从person2中查找**/
			Object value = Ognl.getValue("name", context, person2);
			System.out.println("ognl expression \"name\" evaluation is : " + value);

			/** 获取根对象的"name"属性值  **/
			/** 指定#person2，直接从person1中查找**/
			Object value2 = Ognl.getValue("#person2.name", context, person2);
			System.out.println("ognl expression \"#person2.name\" evaluation is : "+ value2);

			/** 获取person1对象的"name"属性值 **/
			/** 指定#person1，直接从person1中查找**/
			Object value3 = Ognl.getValue("#person1.name", context, person2);
			System.out.println("ognl expression \"#person1.name\" evaluation is : "+ value3);

			/** 将person4指定为root对象，获取person4对象的"name"属性，注意person4对象不在上下文中 **/
			/** 从根对象person4中查找，找到 **/
			Object value4 = Ognl.getValue("name", context, person4);
			System.out.println("ognl expression \"name\" evaluation is : "+ value4);

			/** 将person4指定为root对象，获取person4对象的"name"属性，注意person4对象不在上下文中 **/
			/** 不存在上下文中，找不到，报错 **/
			Object value5 = Ognl.getValue("#person4.name", context, person4);
			System.out.println("ognl expression \"person4.name\" evaluation is : "+ value5);
		} catch (OgnlException e) {
			e.printStackTrace();
		}
	}
}

4.OGNL调用方法

public class OGNL2 {
	public static void main(String[] args) { /* OGNL提供的一个上下文类，它实现了Map接口 */
		OgnlContext context = new OgnlContext();
		People people1 = new People();
		people1.setName("zhangsan");
		People people2 = new People();
		people2.setName("lisi");
		People people3 = new People();
		people3.setName("wangwu");
		context.put("people1", people1);
		context.put("people2", people2);
		context.put("people3", people3);
		context.setRoot(people1);
		try {
			/** 调用 成员方法 **/
			Object value = Ognl.getValue("name.length()", context, context.getRoot());
			System.out.println("people1 name length is :" + value);
			Object upperCase = Ognl.getValue("#people2.name.toUpperCase()", context, context.getRoot());
			System.out.println("people2 name upperCase is :" + upperCase);
			Object invokeWithArgs = Ognl.getValue("name.charAt(5)", context, context.getRoot());
			System.out.println("people1 name.charAt(5) is :" + invokeWithArgs);
			/** 调用静态方法 **/
			Object min = Ognl.getValue("@java.lang.Math@min(4,10)", context, context.getRoot());
			System.out.println("min(4,10) is :" + min);
			/** 调用静态变量 **/
			Object e = Ognl.getValue("@java.lang.Math@E", context, context.getRoot());
			System.out.println("E is :" + e);
		} catch (OgnlException e) {
			e.printStackTrace();
		}
	}
}

5.OGNL操作集合

public class OGNL3 {
	public static void main(String[] args) throws Exception {
		OgnlContext context = new OgnlContext();
		Classroom classroom = new Classroom();
		classroom.getStudents().add("zhangsan");
		classroom.getStudents().add("lisi");
		classroom.getStudents().add("wangwu");
		classroom.getStudents().add("zhaoliu");
		classroom.getStudents().add("qianqi");
		Student student = new Student();
		student.getContactWays().put("homeNumber", "110");
		student.getContactWays().put("companyNumber", "119");
		student.getContactWays().put("mobilePhone", "112");
		context.put("classroom", classroom);
		context.put("student", student);
		context.setRoot(classroom); /* 获得classroom的students集合 */
		Object collection = Ognl.getValue("students", context,context.getRoot());
		System.out.println("students collection is ：" + collection); /* 获得classroom的students集合 */
		Object firstStudent = Ognl.getValue("students[0]", context,context.getRoot());
		System.out.println("first student is : " + firstStudent); /* 调用集合的方法 */
		Object size = Ognl.getValue("students.size()", context,context.getRoot());
		System.out.println("students collection size is :" + size);
		System.out.println("--------------------------飘逸的分割线--------------------------");
		Object mapCollection = Ognl.getValue("#student.contactWays", context,context.getRoot());
		System.out.println("mapCollection is :" + mapCollection);"#student.contactWays['homeNumber']", context, context.getRoot());
		System.out.println("the first element of contactWays is :" + firstElement);
		System.out.println("--------------------------飘逸的分割线--------------------------"); /* 创建集合 */
		Object createCollection = Ognl.getValue("{'aa','bb','cc','dd'}", context, context.getRoot());
		System.out.println(createCollection); /* 创建Map集合 */
		Object createMapCollection = Ognl.getValue("#{'key1':'value1','key2':'value2'}", context, context.getRoot());
		System.out.println(createMapCollection);
	}
}

class Classroom {
	private List<String> students = new ArrayList<String>();

	public List<String> getStudents() {
		return students;
	}

	public void setStudents(List<String> students) {
		this.students = students;
	}
}

class Student {
	private Map<String, Object> contactWays = new HashMap<String, Object>();

	public Map<String, Object> getContactWays() {
		return contactWays;
	}

	public void setContactWays(Map<String, Object> contactWays) {
		this.contactWays = contactWays;
	}
}

6.OGNL过滤集合

public class OGNL4 {
	public static void main(String[] args) throws Exception {
		OgnlContext context = new OgnlContext();
		Humen humen = new Humen();
		humen.setName("qiuyi");
		humen.setSex("n");
		humen.setAge(22);
		humen.getFriends().add(new Humen("zhangsan", "n", 22));
		humen.getFriends().add(new Humen("lisi", "f", 21));
		humen.getFriends().add(new Humen("wangwu", "n", 23));
		humen.getFriends().add(new Humen("zhaoliu", "n", 22));
		humen.getFriends().add(new Humen("qianqi", "n", 22));
		humen.getFriends().add(new Humen("sunba", "f", 20));
		humen.getFriends().add(new Humen("yangqiu", "f", 25));
		context.put("humen", humen);
		context.setRoot(humen);
		/** OGNL过滤集合的语法为：collection.{? expression} **/
		Object filterCollection = Ognl.getValue("friends.{? #this.name.length() > 7}", context, context.getRoot());
		System.out.println("filterCollection is :" + filterCollection);
		System.out.println("--------------------------飘逸的分割线--------------------------");
		/** OGNL投影集合的语法为：collection.{expression} **/
		Object projectionCollection = Ognl.getValue("friends.{name}", context, context.getRoot());
		System.out.println("projectionCollection is :" + projectionCollection);
	}
}

class Humen {
	private String name;
	private String sex;
	private int age;
	private List<Humen> friends = new ArrayList<Humen>();

	public Humen() {
	}

	public Humen(String name, String sex, int age) {
		this.name = name;
		this.sex = sex;
		this.age = age;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public List<Humen> getFriends() {
		return friends;
	}

	public void setFriends(List<Humen> friends) {
		this.friends = friends;
	}

	@Override
	public String toString() {
		return "Humen [name=" + name + ", sex=" + sex + ", age=" + age + "]";
	}
}

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转载自【宝宝巴士SuperDo团队】原文链接: http://www.cnblogs.com/superdo/p/5080281.html