Learn OGNL grammar

Original link: http://www.yiidian.com/struts2/struts2-ognl.html

1 Introduction to OGNL

OGNLThe full name of is Object-Graph Navigation Language (Object-Graph Navigation Language), which is a powerful open source expression language. Using this expression language, you can store any attributes of Java objects through a certain expression syntax and call The methods of Java objects can also automatically implement the necessary type conversion. If the expression is regarded as a string with semantics, then OGNL has undoubtedly become the communication bridge between this semantic string and Java objects.

2 OGNL data structure

OGNL expressions operate on an OgnlContextobject called . This object contains two properties:

• root: root object, any object can be stored as a Root object
• context: Context object, this is a Map structure, any key-value key-value pair can be stored in this Map

Both of the above two attributes of the OgnlContext object, we can use the OGNL expression for data access.

3 OGNL expression syntax

Ognl expression basic rules:

• To take the value of the root object, just pass the root object properties directly

• To get the value of the context object, you must take it through the #key. Attribute in the specified context container

3.1 Environmental preparation

First import the ognl package to the project

Design a User class for storing data

package com.yiidian.ognl;
/**
 * @author 一点教程(yiidian.com)
 */
public class User {
	private String name;
	private Integer age;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getAge() {
		return age;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
	public User() {
		super();
	}
	public User(String name, Integer age) {
		super();
		this.name = name;
		this.age = age;
	}
	
}

3.2 Basic values

/**
 * 基本取值
 */
@Test
// 取出root中的属性值
public void test1() throws Exception {
	// 准备ONGLContext
	// 准备Root
	User rootUser = new User("tom", 18);
	// 准备Context
	Map<String, User> context = new HashMap<String, User>();
	context.put("user1", new User("jack", 18));
	context.put("user2", new User("rose", 22));
	OgnlContext oc = new OgnlContext();
	oc.setRoot(rootUser);
	oc.setValues(context);
	
	// ====使用OGNL表达式取出属性====
	// 取出root中user对象的name属性
	String name = (String) Ognl.getValue("name", oc, oc.getRoot());
	Integer age = (Integer) Ognl.getValue("age", oc, oc.getRoot());
	System.out.println(name);
	System.out.println(age);

	// ---------------------------------------------------
	// 取出context中键为user1对象的name属性
	String name1 = (String) Ognl.getValue("#user1.name", oc, oc.getRoot());
	String name2 = (String) Ognl.getValue("#user2.name", oc, oc.getRoot());
	Integer age1 = (Integer) Ognl.getValue("#user2.age", oc, oc.getRoot());
	System.out.println(name1);
	System.out.println(name2);
	System.out.println(age1);
}

The result is:

3.3 Assignment

/**
 * 赋值
 */
@Test
public void test2() throws Exception {
	// 准备ONGLContext
	// 准备Root
	User rootUser = new User("tom", 18);
	// 准备Context
	Map<String, User> context = new HashMap<String, User>();
	context.put("user1", new User("jack", 18));
	context.put("user2", new User("rose", 22));
	OgnlContext oc = new OgnlContext();
	oc.setRoot(rootUser);
	oc.setValues(context);
	
	// 编写OGNL表达式
	// 将root中的user对象的name属性赋值
	Ognl.getValue("name='jerry'", oc, oc.getRoot());
	String name = (String) Ognl.getValue("name", oc, oc.getRoot());

	String name2 = (String) Ognl.getValue("#user1.name='张三',#user1.name",oc, oc.getRoot());
	System.out.println(name);
	System.out.println(name2);
}

The result is:

3.4 Calling methods

/**
 * 调用方法
 */
@Test
public void test3() throws Exception  {
	// 准备ONGLContext
	// 准备Root
	User rootUser = new User("tom", 18);
	// 准备Context
	Map<String, User> context = new HashMap<String, User>();
	context.put("user1", new User("jack", 18));
	context.put("user2", new User("rose", 22));
	OgnlContext oc = new OgnlContext();
	oc.setRoot(rootUser);
	oc.setValues(context);
	
	// 编写OGNL表达式
	// 调用root中user对象的setName方法
	Ognl.getValue("setName('lilei')", oc, oc.getRoot());
	String name = (String) Ognl.getValue("getName()", oc, oc.getRoot());

	String name2 = (String) Ognl.getValue("#user1.setName('lucy'),#user1.getName()", oc, oc.getRoot());

	System.out.println(name);
	System.out.println(name2);
}

The result is:

3.5 Calling a static method

1) Design an OgnlUtil class with a static method sayHello

package com.yiidian.ognl;
/**
 * @author 一点教程(yiidian.com)
 */
public class OgnlUtil {

	public static String sayHello(String name){
		return "你好，"+name;
	}
}
使用Ognl表达式调用sayHello静态方法

/**
 * 调用静态方法
 */
@Test
public void test4() throws Exception {
	// 准备ONGLContext
	// 准备Root
	User rootUser = new User("tom", 18);
	// 准备Context
	Map<String, User> context = new HashMap<String, User>();
	context.put("user1", new User("jack", 18));
	context.put("user2", new User("rose", 22));
	OgnlContext oc = new OgnlContext();
	oc.setRoot(rootUser);
	oc.setValues(context);
	
	// 编写OGNL表达式
	String name = (String) Ognl.getValue("@com.yiidian.ognl.OgnlUtil@sayHello('张三')", oc,oc.getRoot());
	Double pi = (Double) Ognl.getValue("@@PI", oc, oc.getRoot());
	System.out.println(name);
	System.out.println(pi);
}

3.6 Create objects (List, Map)

/**
 * 创建对象(List、Map)
 */
@Test
public void test5() throws Exception {
	// 准备ONGLContext
	// 准备Root
	User rootUser = new User("tom", 18);
	// 准备Context
	Map<String, User> context = new HashMap<String, User>();
	context.put("user1", new User("jack", 18));
	context.put("user2", new User("rose", 22));
	OgnlContext oc = new OgnlContext();
	oc.setRoot(rootUser);
	oc.setValues(context);
	
	// 编写OGNL表达式
	// 创建list对象
	Integer size = (Integer) Ognl.getValue("{'tom','jerry','jack','rose'}.size()", oc, oc.getRoot());
	String name = (String) Ognl.getValue("{'tom','jerry','jack','rose'}[0]", oc, oc.getRoot());
	String name2 = (String) Ognl.getValue("{'tom','jerry','jack','rose'}.get(1)", oc, oc.getRoot());
	
	System.out.println(size); 
	System.out.println(name);
	System.out.println(name2);
	 
	// 创建Map对象
	Integer size2 = (Integer) Ognl.getValue("#{'name':'tom','age':18}.size()", oc, oc.getRoot());
	String name3 = (String) Ognl.getValue("#{'name':'tom','age':18}['name']", oc, oc.getRoot());
	Integer age = (Integer) Ognl.getValue("#{'name':'tom','age':18}.get('age')", oc, oc.getRoot());
	System.out.println(size2);
	System.out.println(name3);
	System.out.println(age);
}

The result is:

Source code download: https://pan.baidu.com/s/1lD59FmfQLsG1h1Yvx55WUg

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