Java Web Learning Chapter 10 - Filter

catalogue

Filter filter

1,Filter Filter it is JavaWeb One of the three components of. The three components are: Servlet Procedures Listener Listener Filter filter

2,Filter Filter it is JavaEE Specifications. That is, the interface

3,Filter Filter is used to: Intercept request , filter the response.

Common application scenarios for intercepting requests include:

1. Permission check

2. Journal operation

3. Transaction management

... wait

Filter instance

Requirement: in your web Under the project, there is one admin catalogue this admin All resources in the directory( html Page jpg Pictures jsp Files, etc.) must be Access is not allowed until the user logs in .

Thinking: according to what we have learned before, we know that after a user logs in, the user's login information will be saved to the Session Domain. Therefore, to check whether the user logs in, you can judge whether the Session contains the user login information!!!

<%
    Object user = session.getAttribute("user");
    // If it is equal to null, it indicates that you have not logged in
    if (user == null) {
        request.getRequestDispatcher("/login.jsp").forward(request,response);
        return;
    }
%>

The above method is only suitable for JSP, so it has limitations

Filter Workflow diagram of:

The Filter filter will intercept the address to be accessed and judge whether it has access permission.

Use steps of Filter:

1. Write a class to implement Filter Interface

2. Implement the filtering method doFilter()

3. To web.xml De configuration in Filter Interception path

Filter Code of:

public class AdminFilter implements Filter {
    /**
    * doFilter Method, which is specially used to intercept requests. Permission checks can be performed
    */
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
        HttpSession session = httpServletRequest.getSession();
        Object user = session.getAttribute("user");
        // If it is equal to null, it indicates that you have not logged in
        if (user == null) {     servletRequest.getRequestDispatcher("/login.jsp").forward(servletRequest,servletResponse);
        return;
        } else {
        // Let the program continue to access the user's target resources
        filterChain.doFilter(servletRequest,servletResponse);
        }
    }
}

filterChain.doFilter(servletRequest,servletResponse);

web.xml Configuration in:

<!--filter Label is used to configure a Filter filter-->
<filter>
    <!--to filter Create an alias-->
    <filter-name>AdminFilter</filter-name>
    <!--to configure filter Full class name of-->
    <filter-class>com.atguigu.filter.AdminFilter</filter-class>
</filter>
<!--filter-mapping to configure Filter Intercepting path of filter-->
<filter-mapping>
    <!--filter-name Indicates to which of the current interception paths filter use-->
    <filter-name>AdminFilter</filter-name>
    <!--url-pattern Configure interception path
    / Indicates that the request address is: http://ip:port / Project path / web Directory mapped to IDEA
    /admin/* Indicates that the request address is: http://ip:port / Project path / admin/*
    -->
<url-pattern>/admin/*</url-pattern>
</filter-mapping>

Complete user login

This is the login page. login.jsp page <br>
    <form action="http://localhost:8080/15_filter/loginServlet" method="get">    
        user name:<input type="text" name="username"/> <br>
        password:<input type="password" name="password"/> <br>
    <input type="submit" />
</form>

LoginServlet program

public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException,IOException {
        resp.setContentType("text/html; charset=UTF-8");
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        if ("wzg168".equals(username) && "123456".equals(password)) {
            req.getSession().setAttribute("user",username);
            resp.getWriter().write("Login succeeded!!!");
        } else {
        req.getRequestDispatcher("/login.jsp").forward(req,resp);
        }
    }
}

Filter lifecycle

Filter The lifecycle of contains several methods

1. Constructor method

2,init Initialization method

Chapter 1, 2 Step, in web Execute when the project starts( Filter (already created)

3,doFilter Filtering method

Step 3: every time a request is intercepted, it will be executed

4,destroy Destroy

Step 4, stop the web When the project is completed, it will be executed (stopped) web The project will also be destroyed Filter Filter)

FilterConfig class

FilterConfig Class sees the name and knows the meaning. It is Filter The profile class for the filter.

Every time Tomcat creates a Filter At the same time, one will be created FilterConfig Class, which contains Filter Configuration information for the configuration file.

The role of the FilterConfig class is to obtain the filter Configuration content of filter

1. Gets the name of the Filter filter-name Content of

2. Gets the value configured in the Filter init-param Initialization parameters

3. Get ServletContext object

java code:

@Override
public void init(FilterConfig filterConfig) throws ServletException {
    System.out.println("2.Filter of init(FilterConfig filterConfig)initialization");
    //1. Get the name of Filter and the content of Filter name 
    System.out.println("filter-name The values are:" + filterConfig.getFilterName());

    //2. Get the init param initialization parameters configured in web.xml 
    System.out.println("username The values are:" + filterConfig.getInitParameter("username"))
    System.out.println("url The values are:" + filterConfig.getInitParameter("url"));

    //3. Get ServletContext object 
    System.out.println(filterConfig.getServletContext());
}

web.xml to configure:

<!--filter Label is used to configure a Filter filter-->
<filter>
    <!--to filter Create an alias-->
    <filter-name>AdminFilter</filter-name>
    <!--to configure filter Full class name of-->
    <filter-class>com.atguigu.filter.AdminFilter</filter-class>

    <init-param>
        <param-name>username</param-name>
        <param-value>root</param-value>
    </init-param>
    <init-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost3306/test</param-value>
    </init-param>
</filter>

FilterChain filter chain

Intercepting path of Filter

-- Exact match

< url-pattern >/target.jsp</url-pattern>

The path configured above indicates that the request address must be: http://ip:port/ Engineering path /target.jsp

-- Directory matching

< url-pattern >/admin/*</url-pattern>

The path configured above indicates that the request address must be: http://ip:port/ Engineering path /admin/*

-- Suffix matches (don't / before the address at this time)

< url-pattern >*.html</url-pattern>

The path configured above indicates that the request address must end in. html to be intercepted

< url-pattern >*.do</url-pattern>

The path configured above indicates that the request address must end with. do before it can be intercepted

< url-pattern >*.action</url-pattern>

The path configured above indicates that the request address must end with. action before it can be intercepted

Filter filter only cares about whether the requested address matches, not whether the requested resource exists!!!

Keywords: Java

Added by mac25 on Fri, 22 Oct 2021 14:18:34 +0300

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