apache-commons 工具包学习

Commons是apache下属的开源子项目，专门提供一些通用的工具类。

这些方法用起来后，程序看起来更加简单，专业。

Commons的主要类结构：

 

Attributes	Runtime API to metadata attributes such as doclet tags.
BeanUtils	Easy-to-use wrappers around the Java reflection and introspection APIs.
Betwixt	Services for mapping JavaBeans to XML documents, and vice versa.
Chain	Chain of Responsibility pattern implemention.
CLI	Command Line arguments parser.
Codec	General encoding/decoding algorithms (for example phonetic, base64, URL).
Collections	Extends or augments the Java Collections Framework.
Compress	Defines an API for working with tar, zip and bzip2 files.
Configuration	Reading of configuration/preferences files in various formats.
Daemon	Alternative invocation mechanism for unix-daemon-like java code.
DBCP	Database connection pooling services.
DbUtils	JDBC helper library.
Digester	XML-to-Java-object mapping utility.
Discovery	Tools for locating resources by mapping service/reference names to resource names.
EL	Interpreter for the Expression Language defined by the JSP 2.0 specification.
Email	Library for sending e-mail from Java.
Exec	API for dealing with external process execution and environment management in Java.
FileUpload	File upload capability for your servlets and web applications.
IO	Collection of I/O utilities.
JCI	Java Compiler Interface
Jelly	XML based scripting and processing engine.
Jexl	Expression language which extends the Expression Language of the JSTL.
JXPath	Utilities for manipulating Java Beans using the XPath syntax.
Lang	Provides extra functionality for classes in java.lang.
Launcher	Cross platform Java application launcher.
Logging	Wrapper around a variety of logging API implementations.
Math	Lightweight, self-contained mathematics and statistics components.
Modeler	Mechanisms to create Model MBeans compatible with JMX specification.
Net	Collection of network utilities and protocol implementations.
Pool	Generic object pooling component.
Primitives	Smaller, faster and easier to work with types supporting Java primitive types.
Proxy	Library for creating dynamic proxies.
Sanselan	A pure-Java image library.
SCXML	An implementation of the State Chart XML specification aimed at creating and maintaining a Java SCXML engine. It is capable of executing a state machine defined using a SCXML document, and abstracts out the environment interfaces.
Transaction	Implementations for multi level locks, transactional collections and transactional file access.
Validator	Framework to define validators and validation rules in an xml file.
VFS	Virtual File System component for treating files, FTP, SMB, ZIP and such like as a single logical file system.

Lang

Lang Provides extra functionality for classes in java.lang.

 

org.apache.commons.lang.builder. ToStringBuilder:

提供object重写toString()的工具类.

ApplicationToStringStyle.APP_TO_STRING_STYLE提供toString的style。

Fruit中重写了toString方法。

 

public abstract class ApplicationToStringStyle extends ToStringStyle {

    private static final long serialVersionUID = 1L;
    
    public static final ApplicationToStringStyle APP_TO_STRING_STYLE = new CustomToStringStyle();

    /**
     * Constructor
     *
     * Use the static constant rather than instantiating
     */
	private static final class CustomToStringStyle extends ApplicationToStringStyle {

		private static final long serialVersionUID = -4289672936337739486L;

		public CustomToStringStyle() {
	        super();
	        this.setUseClassName(true);
	        this.setUseIdentityHashCode(false);
	        this.setContentStart(SystemUtils.LINE_SEPARATOR + "[");
	        this.setFieldSeparator(SystemUtils.LINE_SEPARATOR + "  ");
	        this.setFieldSeparatorAtStart(true);
	        this.setContentEnd(SystemUtils.LINE_SEPARATOR + "]");
	        
	        this.setUseShortClassName(true);
	    }

	    /**
	     * Override the append() method to skip fields that start with "_".  In this
	     * application, Axis generates some fields using this prefix that we don't want to include
	     * in the log files.  
	     */
		@Override
	    public void append(StringBuffer buffer, String fieldName, Object value, Boolean fullDetail) {
	    	if (fieldName != null && !fieldName.startsWith("_")) {
	    		super.append(buffer, fieldName, value, fullDetail);
	    	}
	    }
	
	    /**
	     * Ensure Singleton after serialization
	     *
	     * @return the singleton
	     */
	    private Object readResolve() {
	        return ApplicationToStringStyle.APP_TO_STRING_STYLE;
	    }
	}   
}

 

public class Fruit {
    private String name = "apple";
    private String size = "3";
    private String price = "$40";

    public String toString() {
        return ReflectionToStringBuilder.toString(this, ApplicationToStringStyle.APP_TO_STRING_STYLE);
    }
}

 

HttpClient

The Commons HttpClient project used to be a part of Commons, but is now part of Apache HttpComponents - see Jakarta Commons HttpClient

 

用于http有关的连接，包括ssl等。

 

Notice that we go through the entire process regardless of whether the server returned an error or not. This is important because HTTP 1.1 allows multiple requests to use the same connection by simply sending the requests one after the other. Obviously, if we don't read the entire response to the first request, the left over data will get in the way of the second response. HttpClient tries to handle this but to avoid problems it is important to always release the connection.

 

基本http get访问 ：

package commons.httpclient;

import java.io.IOException;

import org.apache.commons.httpclient.DefaultHttpMethodRetryHandler;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.HttpException;
import org.apache.commons.httpclient.HttpStatus;
import org.apache.commons.httpclient.methods.GetMethod;
import org.apache.commons.httpclient.params.HttpMethodParams;

public class Test {
    
    public static void main(String[] args) throws HttpException, IOException {
        //1. Create an instance of HttpClient. 
        HttpClient client = new HttpClient();
        
        //2.
        //Create an instance of one of the methods (GetMethod in this case). 
        //The URL to connect to is passed in to the the method constructor.
        GetMethod method = new GetMethod("http://www.baidu.com/");
        
        method.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, 
                new DefaultHttpMethodRetryHandler(3, false));
        
        //3.Tell HttpClient to execute the method.
        int statusCode = client.executeMethod(method);

        if (statusCode != HttpStatus.SC_OK) {
            System.err.println("Method failed: " + method.getStatusLine());
          }
        
        //4.Read the response. 
        String reponse = method.getResponseBodyAsString();
        
        //5.Release the connection. 
        method.releaseConnection();
        
        //6.Deal with the response. 
        System.out.println(reponse);
    }
    
}