The technical principle of the postcss framework in the Java library
PostCSS is a JavaScript tool that helps developers to use modern CSS syntax in CSS and automatically handle browser compatibility issues.It is a framework that can be extended through the plug -in mechanism. It can automatically process CSS code and generate CSS code that the target browser can understand.
The technical principles of postcss are as follows:
1. Plug -in system: PostCSS uses plug -in to process CSS code.It allows developers to choose and configure various plug -in according to their needs, so as to achieve custom processing CSS.
2. AST (abstract grammar tree): PostCSS uses AST to analyze and convert CSS code.It analyzes the CSS code into an abstract syntax tree, and then operates this syntax tree through the plug -in to modify, operate, and add nodes.
3. The execution order of the plug -in: Postcss plug -in is called according to a certain execution order. You can specify the execution order of the plug -in by configuration.Each plug -in is specific to the CSS code, and then pass the result to the next plug -in to continue processing until all the plug -in is executed.
4. CSS code conversion: PostCSS plug -in can perform various conversion operations on the CSS code, such as adding browser prefix, compressed CSS code, optimizing the CSS structure, etc.Developers can choose the appropriate plug -in according to the requirements of the project, and flexibly configure the plug -in option to realize the conversion of the CSS code.
5. Caches and analysis: POSTCSS improves processing speed by caching and parsing.When a CSS file is modified, PostCSS will resume the file and cache the result.When processed next time, postcss will check the cache first. If there is no change, use the cache result to improve the processing speed.
Below is a sample code and related configuration files using the Java library of PostCSS:
1. Introduce the Java library of postcss in the project. You can use Maven to manage dependencies:
<dependency>
<groupId>org.postcss</groupId>
<artifactId>postcss</artifactId>
<version>version_number</version>
</dependency>
2. Create a postcss configuration file (postcss.config.js), configure plug -in and its options:
script
module.exports = {
plugins: [
Require ('Autoprefixer') ({BrowSers: [Last 2 Versions']}), // Add the browser prefix
Require ('cssnano') () // Compressed CSS code
]
}
3. Use PostCSS to process CSS code in Java code:
import org.postcss.PostCss;
import org.postcss.ProcessingException;
import org.postcss.Result;
import org.postcss.parser.Parser;
import org.postcss.processor.Processor;
import org.postcss.processor.ProcessorOptions;
import java.io.File;
import java.io.IOException;
public class PostCSSExample {
public static void main(String[] args) {
String inputFile = "path_to_input_file";
String outputFile = "path_to_output_file";
try {
File input = new File(inputFile);
File output = new File(outputFile);
// Read the input file and parse it into AST
Parser parser = new Parser();
Result result = parser.parse(input);
// Create a processor and load the configuration file
Processor processor = PostCss.postcss();
ProcessorOptions options = new ProcessorOptions();
options.setConfigPath ("PATH_TO_POSTCSS.CONFIG.JS"); // Configure the file path
processor.setOptions(options);
// Treat the CSS code
Result processed = processor.process(result);
// Write the processing CSS code into the output file
processed.save(output);
System.out.println ("CSS processing is complete!");
} catch (IOException | ProcessingException e) {
e.printStackTrace();
}
}
}
In the above examples, we first parsed the CSS file into AST through PASTCSS's Parser.Then, create a processor (processor) and load the configuration file.The configuration file specifies two plug -in: AutoPREFIXER and CSSNANO.Finally, process the CSS code through the processor and write the results into the output file.
