DWR introduction and usage

introduce

It consists of two main parts: allowing JavaScript to obtain data from a Servlet on a WEB server that follows the AJAX principle. On the other hand, a JavaScript library can help website developers easily use the obtained data to dynamically change the content of the web page.

DWR takes a new approach similar to AJAX to dynamically generate JavaScript code based on JAVA classes. In this way, WEB developers can use Java code in JavaScript as if they were local code (client-side code) of the browser; but Java code runs on the WEB server and can freely access the resources of the WEB server. For security reasons, WEB developers must properly configure which Java classes can be safely used externally. This Java-to-JavaScript approach to remote functionality gives DWR users an interface that looks very much like traditional RPC mechanisms, like RMI or SOAP, but with the benefit of running on the web without the need for browser plugins. DWR does not consider browser/web server protocols important, but is more interested in ensuring a simple and natural programming interface. The biggest challenge is to combine the asynchronous nature of AJAX with the synchronous nature of normal JAVA method calls. In asynchronous mode, the result data can only be obtained by asynchronous access some time after the call is started. DWR allows web developers to pass a callback function to asynchronously handle the Java function call process. In addition, .dwr is also a file format: For example, in Dreamweaver software, there is a search and replace function, and the frequently used search and replace content can be saved, and the saved file ends with .dwr. This kind of file can be opened with Notepad to see its content.

How to use

1.1、Configuration of dwr.xml

The tag contains things that can be exposed to JavaScript.

The tag specifies the Java class that can be accessed in JavaScript and defines how DWR should obtain an instance of the class to be remoted. The creator="new" attribute specifies how the Java class instance is generated. New means that DWR should call the default constructor of the class to obtain the instance. There are other spring methods, such as obtaining the instance by integrating with the IOC container Spring, etc. The javascript=" testClass " attribute specifies the name used by the JavaScript code to access the object.

The tag specifies the Java class name to be exposed to JavaScript.

The tag specifies the methods to be exposed to JavaScript. If not specified, all methods will be exposed.

The tag specifies methods to prevent access.

1.2、Calling in javascript

First, import the javascript script

Among them, TestClass.js is automatically generated by dwr according to the configuration file, and engine.js and util.js are script files that come with dwr.

Second, write a javascript function that calls the java method

Function callTestMethod1(){

testClass.testMethod1();

}

2. Calling a Java method with a simple return value

2.1、Configuration of dwr.xml

Same configuration as 1.1

2.2、Calling in javascript

First, import the javascript script

Secondly, write a javascript function that calls the java method and a callback function that receives the return value

Function callTestMethod2(){

testClass.testMethod2(callBackFortestMethod2);

}

Function callBackFortestMethod2(data){

//The return value of the data receiving method

//You can process and display the return value here, etc.

alert("the return value is " + data);

}

Where callBackFortestMethod2 is the callback function that receives the return value

3. Calling Java methods with simple parameters

3.1、Configuration of dwr.xml

Same configuration as 1.1

3.2、Calling in javascript

First, import the javascript script

Second, write a javascript function that calls the java method

Function callTestMethod3(){

//Define the parameters to be passed to the java method

var data;

//Construction parameters

data = "test String";

testClass.testMethod3(data);

}

4. Call the Java method that returns the JavaBean

4.1、Configuration of dwr.xml

The tag is responsible for exposing classes and class methods for Web remoting, while the tag is responsible for the parameters and return types of these methods. The function of the convert element is to tell DWR how to convert data types between server-side Java object representation and serialized JavaScript. DWR automatically adjusts simple data types between Java and JavaScript representation. These types include Java native types and their respective encapsulated class representations, as well as String, Date, array, and collection types. DWR can also convert JavaBeans into JavaScript representations, but for security reasons, explicit configuration is required. The tag completes this function. The converter="bean" attribute specifies that the conversion method uses the JavaBean naming specification, the match=""com.dwr.TestBean" attribute specifies the javabean name to be converted, and the tag specifies the JavaBean property to be converted.

4.2、Calling in javascript

First, import the javascript script

Secondly, write a javascript function that calls the java method and a callback function that receives the return value

Function callTestMethod4(){

testClass.testMethod4(callBackFortestMethod4);

}

Function callBackFortestMethod4(data){

//The return value of the data receiving method

//There are two ways to handle the JavaBean return value

//When you don't know the attribute name, use the following method

for(var property in data){

alert("property:"+property);

alert(property+":"+data[property]);

}

//When you know the attribute name, use the following method

alert(data.username);

alert(data.password);

}

Where callBackFortestMethod4 is the callback function that receives the return value

5. Calling Java methods with JavaBean parameters

5.1、Configuration of dwr.xml

Same configuration as 4.1

5.2、Calling in javascript

First, import the javascript script

Second, write a javascript function that calls the java method

Function callTestMethod5(){

//Define the parameters to be passed to the java method

var data;

//Construction parameters, data is actually an object

data = { username:"user", password:"password" }

testClass.testMethod5(data);

}

6. Call a Java method that returns a List, Set, or Map

6.1、Configuration of dwr.xml

Same configuration as 4.1

Note: If the elements in List, Set, or Map are simple types (including their encapsulated classes) or String, Date, array, and collection types, the tag is not required.

6.2、Call in javascript (taking returning List as an example, the element of List is TestBean)

First, import the javascript script

Secondly, write a javascript function that calls the java method and a callback function that receives the return value

Function callTestMethod6(){

testClass.testMethod6(callBackFortestMethod6);

}

Function callBackFortestMethod6(data){

//The return value of the data receiving method

//There are two ways to handle the JavaBean return value

//When you don't know the attribute name, use the following method

for(var i=0;i