Common problems and solutions of the UNDERSCORE framework in the Java library
Common problems and solutions of the UNDERSCORE framework in the Java library
The UNDERSCORE framework is a JavaScript tool library. In order to facilitate the use of the UNDERSCORE framework in the Java library, we can use the Rhino engine to perform the JavaScript script in the Java code.However, some common problems are often encountered in using the UNDERSCORE framework. This article will introduce these problems and its solutions and provide corresponding Java code examples.
Question 1: How to install the Underscore framework in the Java library?
Solution: First, we need to introduce Rhino dependencies in the project.Then, we can download and install the UNDERSCORE framework through the following Java code:
import org.mozilla.javascript.Context;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;
public class UnderscoreInstaller {
public static void main(String[] args) throws Exception {
Context context = Context.enter();
ScriptableObject scope = context.initStandardObjects();
String underscoreSource = "https://cdn.jsdelivr.net/underscorejs/1.12.0/underscore-min.js";
context.evaluateString(scope, "var scriptURL = new java.net.URL('" + underscoreSource + "');
" +
"var conn = scriptURL.openConnection();
" +
"var reader = new java.io.InputStreamReader(conn.getInputStream());
" +
"var doc = new java.io.BufferedReader(reader);
" +
"var line;
" +
"var script = '';
" +
"while ((line = doc.readLine()) != null) {
" +
" script += line + '\
';
" +
"}
" +
"reader.close();
" +
"context.evaluateString(scope, script, '<underscore>');", "<underscore>", 1, null);
Context.exit();
}
}
Question 2: How to use the UNDERSCORE framework function in the Java library?
Solution: Once the UNDERSCORE framework is installed, we can use its functions in the Java code.The following is an example code that shows how to use the UNDERSCORE framework `Filter` function:
import org.mozilla.javascript.Context;
import org.mozilla.javascript.NativeArray;
import org.mozilla.javascript.ScriptableObject;
public class UnderscoreExample {
public static void main(String[] args) throws Exception {
Context context = Context.enter();
ScriptableObject scope = context.initStandardObjects();
// Assume that the UNDERSCORE framework has been installed
// Create a JavaScript array
NativeArray array = (NativeArray) context.evaluateString(scope, "var array = [1, 2, 3, 4, 5]; array;", "<array>", 1, null);
// Use the Filter function to filter the even number in the array
String script = "var filtered = _.filter(array, function(num) {
" +
" return num % 2 === 0;
" +
"});
" +
"filtered;";
Object filteredArray = context.evaluateString(scope, script, "<filteredArray>", 1, null);
// Traversing the array after filtering and output results
for (int i = 0; i < array.getLength(); i++) {
System.out.println(filteredArray.get(i, null));
}
Context.exit();
}
}
Question 3: How to use the Underscore framework chain grammar in the Java library?
Solution: By using Rhino's `Continuationpending` exception, we can simulate the chain syntax of the UNDERSCORE framework.The following is a sample code that shows how to use the Underscore framework chain syntax in the Java code:
import org.mozilla.javascript.Context;
import org.mozilla.javascript.EcmaError;
import org.mozilla.javascript.Scriptable;
import org.mozilla.javascript.ScriptableObject;
public class UnderscoreChaining {
public static void main(String[] args) throws Exception {
Context context = Context.enter();
ScriptableObject scope = context.initStandardObjects();
// Assume that the UNDERSCORE framework has been installed
// Create a JavaScript array
context.evaluateString(scope, "var array = [1, 2, 3, 4, 5];", "<array>", 1, null);
String script = "var result;
" +
"try {
" +
" result = _.chain(array)
" +
" .filter(function(num) { return num % 2 === 0; })
" +
" .map(function(num) { return num * 2; })
" +
" .value();
" +
"} catch (e) {
" +
" if (e instanceof ContinuationPending) {
" +
" result = e.getContinuation().toString();
" +
" } else {
" +
" throw e;
" +
" }
" +
"}
" +
"result;";
try {
Object result = context.evaluateString(scope, script, "<result>", 1, null);
System.out.println(result);
} catch (EcmaError e) {
if (e.getMessage().equals("ContinuationPending")) {
throw new RuntimeException("Missing ContinuationPending class. Make sure Rhino runtime is properly configured with Continuations enabled.");
} else {
throw e;
}
}
Context.exit();
}
}
In this article, we introduced the common problems and solutions of the UNDERSCORE framework in the Java library and provided the corresponding Java code example.By understanding these problems and solutions, you can better use the Underscore framework in the Java project and speed up development efficiency.
