Introduction to Spring Use (iv)--spel

I. Introduction of SPEL

The spring expression language is all called "Spring expression Language" and is abbreviated as "Spel" to build complex expressions at run-time

Steps to use:

1) Create parser: ExpressionParser interface represents parser, Spelexpressionparser provides default implementation

2) Parse expression: Use the Expressionparser.parseexpression () method to parse an expression into an expressions object

3) Construct context: Used to define variables, represented by Evaluationcontext interfaces, Standardevaluationcontext provides default implementations

4) Evaluation: Use the Expression.getvalue () method to evaluate the value of an expression based on the context

@Test Public voidTestspel () {//Spel ParserExpressionParser parser =NewSpelexpressionparser (); //spel StatementsExpression expression1 = parser.parseexpression ("895"); Assert.asserttrue (895 = = Expression1.getvalue (int.class)); //spel StatementsExpression expression2 = parser.parseexpression ("' Hello '"); Assert.asserttrue (Stringutils.equals ("Hello", Expression2.getvalue (String.class))); //Spel ContextEvaluationcontext context =NewStandardevaluationcontext (); Context.setvariable ("End", "ZZ"); Expression Expression3= Parser.parseexpression (' yy ' + ' pp '). Concat (#end) "); Assert.asserttrue (Stringutils.equals ("Yyppzz", expression3.getvalue (context, String.class)));}

Second, use spel in the bean definition

ApplicationContext implements the default support for Spel, which is injected with the bean definition, using the "#{spel expression}" representation

1) XML mode

<BeanID= "STR1"class= "Java.lang.String">    <Constructor-argIndex= "0"value= "Uouu"/>  </Bean><BeanID= "Propbean"class= "Java.lang.String">    <Constructor-argIndex= "0"value= "#{str1}"/></Bean>

@Test  Public void TestSpel2 () {    new classpathxmlapplicationcontext ("Spring-context.xml");     = Context.getbean ("Propbean", String.  Class);    Assert.asserttrue (Stringutils.equals ("Uouu", prop));}

2) Annotation Method

 public  class   Hello {@Value ( "#{str1}"  private   String password;   public   String GetPassword () { return   password; }}

 <!--  define bean  -->  <  bean  class  = "Cn.matt.spel.Hello"  ></ bean  >  <!--  opening annotations  -->  <  context:annotation-config  />  

@Test  Public void TestSpel3 () {    new classpathxmlapplicationcontext ("Spring-context.xml");     = Context.getbean (Hello.  Class);    Assert.asserttrue (Stringutils.equals ("Uouu", Hello.getpassword ()));

Third, the use of property files

How the Spring properties file is configured:

<!--Full write mode -<BeanID= "Propertyplaceholderconfigurer"class= "Org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">    < Propertyname= "Locations">        <List>            <value>Jdbc1.properties</value>            <value>Jdbc2.properties</value>        </List>    </ Property></Bean>

Shorthand for the above configuration:

<!---<location= "Classpath:jdbc1.properties, Classpath:jdbc2.properties "/>

Examples of usage are as follows:

# jdbc1.properties File username=rootpassword=root

# jdbc2.properties File username=adminpassword=admin

 <  bean  id  = "Propbean"   class  = "java.lang.String"     >  <  constructor-arg  index  = "0"   value  = "${password}"   />  </ bean  >  

@Test  Public void TestSpel2 () {    new classpathxmlapplicationcontext ("Spring-context.xml");     = Context.getbean ("Propbean", String.  Class);    Assert.asserttrue (Stringutils.equals ("admin", prop));}

Note:

1) Spring uses "${property name}" to represent property values, unlike spel using "#{spel expression}"

2) When the same attribute value exists in multiple property files, the latter overrides the former

3) Support annotation mode, using the same way as spel annotation, such as: @Value ("${password}")

Reference:

Fifth 5.1 Overview of Spring Expression Language 5.2 spel Foundation--Follow me to learn Spring3

The fifth Chapter 5.3 Spel Grammar of Spring Expression language--learn from me Spring3

Fifth Spring expression Language 5.4 using el-in the bean definition learn from me spring3

Spring <context:property-placeholder> Instructions for use

Import multiple properties files using <context:property-placeholder> tags

Introduction to Spring Use (iv)--spel