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• Apache Http Java Example
• Apache Http Java Maven

To build a RESTful client using apache httpclient, follow below instruction. Apache HttpClient maven dependency org.apache.httpcomponents httpclient 4.1.1 2. Apache HttpClient GET API Example. Java program for how to send json data using http get request. Java 11 - Standard HTTP Client VS Apache HttpClient In Java 11, the incubated HTTP APIs from Java 9 are now officially incorporated into the Java SE API (as stated in JEP 321 ). The API has seen a few changes, one of them is the API is now fully asynchronous.

• Out of the box, the HttpClient doesn't do preemptive authentication. Instead, this has to be an explicit decision made by the client. First, we need to create the HttpContext – pre-populating it with an authentication cache with the right type of authentication scheme pre-selected.
• The Apache HttpComponents project is responsible for creating and maintaining a toolset of low level Java components focused on HTTP and associated protocols. This project functions under the Apache Software Foundation (and is part of a larger community of developers and users.
• Welcome to the Apache OpenJPA project¶. Apache OpenJPA is a Java persistence project at The Apache Software Foundation that can be used as a stand-alone POJO persistence layer or integrated into any Java EE compliant container and many other lightweight frameworks, such as Tomcat and Spring.

javax.servlet.http
Class HttpServlet

All Implemented Interfaces:

java.io.Serializable, Servlet, ServletConfig

public abstract class HttpServlet

extends GenericServlet

implements java.io.Serializable

Provides an abstract class to be subclassed to create an HTTP servlet suitable for a Web site. A subclass of HttpServlet must override at least one method, usually one of these:

• doGet, if the servlet supports HTTP GET requests
• doPost, for HTTP POST requests
• doPut, for HTTP PUT requests
• doDelete, for HTTP DELETE requests
• init and destroy, to manage resources that are held for the life of the servlet
• getServletInfo, which the servlet uses to provide information about itself

There's almost no reason to override the service method. service handles standard HTTP requests by dispatching them to the handler methods for each HTTP request type (the doXXX methods listed above).

Likewise, there's almost no reason to override the doOptions and doTrace methods.

Servlets typically run on multithreaded servers, so be aware that a servlet must handle concurrent requests and be careful to synchronize access to shared resources. Shared resources include in-memory data such as instance or class variables and external objects such as files, database connections, and network connections. See the Java Tutorial on Multithreaded Programming for more information on handling multiple threads in a Java program.

Version:

$Version$

Author:

Various

See Also:

Serialized Form

Constructor Summary

HttpServlet() Does nothing, because this is an abstract class.

Method Summary
protected void	doDelete(HttpServletRequest req, HttpServletResponse resp) Called by the server (via the service method) to allow a servlet to handle a DELETE request.
protected void	doGet(HttpServletRequest req, HttpServletResponse resp) Called by the server (via the service method) to allow a servlet to handle a GET request.
protected void	doHead(HttpServletRequest req, HttpServletResponse resp) Receives an HTTP HEAD request from the protected service method and handles the request.
protected void	doOptions(HttpServletRequest req, HttpServletResponse resp) Called by the server (via the service method) to allow a servlet to handle a OPTIONS request.
protected void	doPost(HttpServletRequest req, HttpServletResponse resp) Called by the server (via the service method) to allow a servlet to handle a POST request.
protected void	doPut(HttpServletRequest req, HttpServletResponse resp) Called by the server (via the service method) to allow a servlet to handle a PUT request.
protected void	doTrace(HttpServletRequest req, HttpServletResponse resp) Called by the server (via the service method) to allow a servlet to handle a TRACE request.
protected long	getLastModified(HttpServletRequest req) Returns the time the HttpServletRequest object was last modified, in milliseconds since midnight January 1, 1970 GMT.
protected void	service(HttpServletRequest req, HttpServletResponse resp) Receives standard HTTP requests from the public service method and dispatches them to the doXXX methods defined in this class.
void	service(ServletRequest req, ServletResponse res) Dispatches client requests to the protected service method.

Methods inherited from class javax.servlet.GenericServlet

destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, init, log, log

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

HttpServlet

Does nothing, because this is an abstract class.

Method Detail

doGet

Called by the server (via the service method) to allow a servlet to handle a GET request.

Overriding this method to support a GET request also automatically supports an HTTP HEAD request. A HEAD request is a GET request that returns no body in the response, only the request header fields.

When overriding this method, read the request data, write the response headers, get the response's writer or output stream object, and finally, write the response data. It's best to include content type and encoding. When using a PrintWriter object to return the response, set the content type before accessing the PrintWriter object.

The servlet container must write the headers before committing the response, because in HTTP the headers must be sent before the response body.

Where possible, set the Content-Length header (with the ServletResponse.setContentLength(int) method), to allow the servlet container to use a persistent connection to return its response to the client, improving performance. The content length is automatically set if the entire response fits inside the response buffer.

When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set the Content-Length header.

The GET method should be safe, that is, without any side effects for which users are held responsible. For example, most form queries have no side effects. If a client request is intended to change stored data, the request should use some other HTTP method.

The GET method should also be idempotent, meaning that it can be safely repeated. Sometimes making a method safe also makes it idempotent. For example, repeating queries is both safe and idempotent, but buying a product online or modifying data is neither safe nor idempotent.

If the request is incorrectly formatted, doGet returns an HTTP 'Bad Request' message.

Parameters:

req - an HttpServletRequest object that contains the request the client has made of the servlet

resp - an HttpServletResponse object that contains the response the servlet sends to the client

Throws:

java.io.IOException - if an input or output error is detected when the servlet handles the GET request

ServletException - if the request for the GET could not be handled

See Also:

ServletResponse.setContentType(java.lang.String)

getLastModified

Returns the time the HttpServletRequest object was last modified, in milliseconds since midnight January 1, 1970 GMT. If the time is unknown, this method returns a negative number (the default).

Servlets that support HTTP GET requests and can quickly determine their last modification time should override this method. This makes browser and proxy caches work more effectively, reducing the load on server and network resources.

Parameters:

req - the HttpServletRequest object that is sent to the servlet

Returns:

a long integer specifying the time the HttpServletRequest object was last modified, in milliseconds since midnight, January 1, 1970 GMT, or -1 if the time is not known

doHead

Receives an HTTP HEAD request from the protected service method and handles the request. The client sends a HEAD request when it wants to see only the headers of a response, such as Content-Type or Content-Length. The HTTP HEAD method counts the output bytes in the response to set the Content-Length header accurately.

If you override this method, you can avoid computing the response body and just set the response headers directly to improve performance. Make sure that the doHead method you write is both safe and idempotent (that is, protects itself from being called multiple times for one HTTP HEAD request).

If the HTTP HEAD request is incorrectly formatted, doHead returns an HTTP 'Bad Request' message.

Parameters:

req - the request object that is passed to the servlet

resp - the response object that the servlet uses to return the headers to the clien

Throws:

java.io.IOException - if an input or output error occurs

ServletException - if the request for the HEAD could not be handled

doPost

Called by the server (via the service method) to allow a servlet to handle a POST request. The HTTP POST method allows the client to send data of unlimited length to the Web server a single time and is useful when posting information such as credit card numbers.

When overriding this method, read the request data, write the response headers, get the response's writer or output stream object, and finally, write the response data. It's best to include content type and encoding. When using a PrintWriter object to return the response, set the content type before accessing the PrintWriter object.

The servlet container must write the headers before committing the response, because in HTTP the headers must be sent before the response body.

Where possible, set the Content-Length header (with the ServletResponse.setContentLength(int) method), to allow the servlet container to use a persistent connection to return its response to the client, improving performance. The content length is automatically set if the entire response fits inside the response buffer.

When using HTTP 1.1 chunked encoding (which means that the response has a Transfer-Encoding header), do not set the Content-Length header.

This method does not need to be either safe or idempotent. Operations requested through POST can have side effects for which the user can be held accountable, for example, updating stored data or buying items online.

If the HTTP POST request is incorrectly formatted, doPost returns an HTTP 'Bad Request' message.

Parameters:

req - an HttpServletRequest object that contains the request the client has made of the servlet

resp - an HttpServletResponse object that contains the response the servlet sends to the client

Throws:

java.io.IOException - if an input or output error is detected when the servlet handles the request

ServletException - if the request for the POST could not be handled

See Also:

ServletOutputStream, ServletResponse.setContentType(java.lang.String)

doPut

Called by the server (via the service method) to allow a servlet to handle a PUT request. The PUT operation allows a client to place a file on the server and is similar to sending a file by FTP.

When overriding this method, leave intact any content headers sent with the request (including Content-Length, Content-Type, Content-Transfer-Encoding, Content-Encoding, Content-Base, Content-Language, Content-Location, Content-MD5, and Content-Range). If your method cannot handle a content header, it must issue an error message (HTTP 501 - Not Implemented) and discard the request. For more information on HTTP 1.1, see RFC 2616 .

This method does not need to be either safe or idempotent. Operations that doPut performs can have side effects for which the user can be held accountable. When using this method, it may be useful to save a copy of the affected URL in temporary storage.

If the HTTP PUT request is incorrectly formatted, doPut returns an HTTP 'Bad Request' message.

Parameters:

req - the HttpServletRequest object that contains the request the client made of the servlet

resp - the HttpServletResponse object that contains the response the servlet returns to the client

Throws:

java.io.IOException - if an input or output error occurs while the servlet is handling the PUT request

ServletException - if the request for the PUT cannot be handled

doDelete

Called by the server (via the service method) to allow a servlet to handle a DELETE request. The DELETE operation allows a client to remove a document or Web page from the server.

This method does not need to be either safe or idempotent. Operations requested through DELETE can have side effects for which users can be held accountable. When using this method, it may be useful to save a copy of the affected URL in temporary storage.

If the HTTP DELETE request is incorrectly formatted, doDelete returns an HTTP 'Bad Request' message.

Parameters:

req - the HttpServletRequest object that contains the request the client made of the servlet

resp - the HttpServletResponse object that contains the response the servlet returns to the client

Throws:

java.io.IOException - if an input or output error occurs while the servlet is handling the DELETE request

ServletException - if the request for the DELETE cannot be handled

doOptions

Called by the server (via the service method) to allow a servlet to handle a OPTIONS request. The OPTIONS request determines which HTTP methods the server supports and returns an appropriate header. For example, if a servlet overrides doGet, this method returns the following header:

Allow: GET, HEAD, TRACE, OPTIONS

There's no need to override this method unless the servlet implements new HTTP methods, beyond those implemented by HTTP 1.1.

Parameters:

req - the HttpServletRequest object that contains the request the client made of the servlet

resp - the HttpServletResponse object that contains the response the servlet returns to the client

Throws:

java.io.IOException - if an input or output error occurs while the servlet is handling the OPTIONS request

ServletException - if the request for the OPTIONS cannot be handled

doTrace

Called by the server (via the service method) to allow a servlet to handle a TRACE request. A TRACE returns the headers sent with the TRACE request to the client, so that they can be used in debugging. There's no need to override this method.

Parameters:

req - the HttpServletRequest object that contains the request the client made of the servlet

resp - the HttpServletResponse object that contains the response the servlet returns to the client

Throws:

java.io.IOException - if an input or output error occurs while the servlet is handling the TRACE request

ServletException - if the request for the TRACE cannot be handled

service

Receives standard HTTP requests from the public service method and dispatches them to the doXXX methods defined in this class. This method is an HTTP-specific version of the Servlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse) method. There's no need to override this method.

Parameters:

req - the HttpServletRequest object that contains the request the client made of the servlet

resp - the HttpServletResponse object that contains the response the servlet returns to the client

Throws:

java.io.IOException - if an input or output error occurs while the servlet is handling the HTTP request

ServletException - if the HTTP request cannot be handled

See Also:

Servlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)

service

Dispatches client requests to the protected service method. There's no need to override this method.

Specified by:

service in interface Servlet

Specified by:

service in class GenericServlet

Parameters:

req - the HttpServletRequest object that contains the request the client made of the servlet

res - the HttpServletResponse object that contains the response the servlet returns to the client

Throws:

java.io.IOException - if an input or output error occurs while the servlet is handling the HTTP request

ServletException - if the HTTP request cannot be handled

See Also:

Servlet.service(javax.servlet.ServletRequest, javax.servlet.ServletResponse)

Overview

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FRAMESNO FRAMESAll Classes SUMMARY: NESTED | FIELD | CONSTR | METHODDETAIL: FIELD | CONSTR | METHODCopyright © 1999-2012 The Apache Software Foundation. All Rights Reserved.

Apache Log4j 2 is an upgrade to Log4j that provides significant improvements over its predecessor, Log4j 1.x, and provides many of the improvements available in Logback while fixing some inherent problems in Logback’s architecture.

Features

API Separation

The API for Log4j is separate from the implementation making it clear for application developers which classes and methods they can use while ensuring forward compatibility. This allows the Log4j team to improve the implementation safely and in a compatible manner.

The Log4j API is a logging facade that may, of course, be used with the Log4j implementation, but may also be used in front of other logging implementations such as Logback. The Log4j API has several advantages over SLF4J: 1. The Log4j API supports logging Messages instead of just Strings. 2. The Log4j API supports lambda expressions. 3. The Log4j API provides many more logging methods than SLF4J. 4. In addition to the “parameterized logging” format supported by SLF4J, the Log4j API also supports events using the java.text.MessageFormat syntax as well printf-style messages. 5. The Log4j API provides a LogManager.shutdown() method. The underlying logging implementation must implement the Terminable interface for the method to have effect. 6. Other constructs such as Markers, log Levels, and ThreadContext (aka MDC) are fully supported.

Improved Performance

Log4j 2 contains next-generation Asynchronous Loggers based on the LMAX Disruptor library. In multi-threaded scenarios Asynchronous Loggers have 18 times higher throughput and orders of magnitude lower latency than Log4j 1.x and Logback. See Asynchronous Logging Performance for details. Otherwise, Log4j 2 significantly outperforms Log4j 1.x, Logback and java.util.logging, especially in multi-threaded applications. See Performance for more information.

Support for multiple APIs

While the Log4j 2 API will provide the best performance, Log4j 2 provides support for the Log4j 1.2, SLF4J, Commons Logging and java.util.logging (JUL) APIs.

Avoid lock-in

Applications coded to the Log4j 2 API always have the option to use any SLF4J-compliant library as their logger implementation with the log4j-to-slf4j adapter.

Automatic Reloading of Configurations

Like Logback, Log4j 2 can automatically reload its configuration upon modification. Unlike Logback, it will do so without losing log events while reconfiguration is taking place.

Advanced Filtering

Like Logback, Log4j 2 supports filtering based on context data, markers, regular expressions, and other components in the Log event. Filtering can be specified to apply to all events before being passed to Loggers or as they pass through Appenders. In addition, filters can also be associated with Loggers. Unlike Logback, you can use a common Filter class in any of these circumstances.

Plugin Architecture

Log4j uses the plugin pattern to configure components. As such, you do not need to write code to create and configure an Appender, Layout, Pattern Converter, and so on. Log4j automatically recognizes plugins and uses them when a configuration references them.

Property Support

You can reference properties in a configuration, Log4j will directly replace them, or Log4j will pass them to an underlying component that will dynamically resolve them. Properties come from values defined in the configuration file, system properties, environment variables, the ThreadContext Map, and data present in the event. Users can further customize the property providers by adding their own Lookup Plugin.

Java 8 Lambda Support

Previously, if a log message was expensive to construct, you would often explicitly check if the requested log level is enabled before constructing the message. Client code running on Java 8 can benefit from Log4j’s lambda support. Since Log4j will not evaluate a lambda expression if the requested log level is not enabled, the same effect can be achieved with less code.

Custom Log Levels

In Log4j 2, custom log levels can easily be defined in code or in configuration. No subclassing is required.

Log Builder API

Apache Http Java Example

In addition to using one of the many log methods in the Log4j API, log events can be constructed using a builder. See [Log Builder][manual/logbuilder.html] for more information.

Garbage-free

During steady state logging, Log4j 2 is garbage-free in stand-alone applications, and low garbage in web applications. This reduces pressure on the garbage collector and can give better response time performance.

Integrating with Application Servers

Version 2.10.0 added the module log4j-appserver to improve integration with Apache Tomcat and Eclipse Jetty.

Cloud Enabled

Version 2.12.0 introduced support for accessing Docker container information via a Lookup and for accessing and updating the Log4j configuration through Spring Cloud Configuration. This support was enhanced in version 2.13.0 to add support for accessing Spring Boot properties as well as Kubernetes information. See Logging in the Cloud for details.

Compatible with Log4j 1.x

The Log4j-1.2-api module of Log4j 2 provides compatiblity for applications using the Log4j 1 logging methods. As of Log4j 2.13.0 Log4j 2 also provides experimental support for Log4j 1.x configuration files. See Log4j 2 Compatiblity with Log4j 1 for more information.

Documentation

The Log4j 2 User’s Guide is available on this site or as a downloadable PDF.

Requirements

Log4j 2.13.0 and greater require Java 8. Version 2.4 through 2.12.1 required Java 7. Some features require optional dependencies; the documentation for these features will specify the required dependencies.

News

Log4j 2.14.1 is now available for production. The API for Log4j 2 is not compatible with Log4j 1.x, however an adapter is available to allow applications to continue to use the Log4j 1.x API. Adapters are also available for Apache Commons Logging, SLF4J, and java.util.logging.

Log4j 2.14.1 is the latest release of Log4j. As of Log4j 2.13.0 Log4j 2 requires Java 8 or greater at runtime. This release contains new features and fixes which can be found in the latest changes report.

Log4j 2.14.0 contains a new Layout, JsonTemplateLayout, that is intended to ultimately replace JsonLayout. As its name suggests it uses a template to define the elements to include in the JSON. This Layout was contributed by the author of the log4j2-logstash-layout at GitHub, and who is now a member of the Log4j community.

Log4j 2.14.0 adds support for MongoDB 4 and removes support for MongoDB 2.

Apache Http Java Maven

Log4j 2.14.1 maintains binary compatibility with previous releases.