SoFunction
Updated on 2025-03-05

Detailed steps for Java to parse complex SQL statements using JSqlParser

1. What is JSqlParser

JSqlParser is a Java library for parsing SQL statements. It parses SQL statements into a Java object tree, allowing you to analyze, modify and operate SQL statements programmatically. It supports a variety of SQL statement types, including but not limited toSELECT、INSERT、UPDATE、DELETE、CREATE、ALTERwait.

For example, for SQL statements"SELECT column1, column2 FROM table1 WHERE column1 = 'value'", JSqlParser can parse it into a Java object, you can easily access various parts of the object, such asSELECTcolumn names in clauses (column1andcolumn2), table name (table1)as well asWHEREConditions in clauses (column1 = 'value')wait.

Here are the steps to install JSqlParser:

1. Use Maven for installation

  • Open your projectdocument.
  • exist<dependencies>Add the following dependencies in the tag:
<dependency>
    <groupId></groupId>
    <artifactId>jsqlparser</artifactId>
    <version>4.4</version>
</dependency>
  • savedocument. Maven will automatically download JSqlParser and its dependencies and add them to your project.

2. Manual download and install (not recommended, omitted)

3. Use Gradle for installation

  • Open your projectdocument.
  • existdependenciesThe following is added in the section:
implementation ':jsqlparser:4.4'
  • Savedocument. Gradle automatically downloads JSqlParser and its dependencies and adds them to your project.

No matter which method you use, once the installation is complete, you can import and use JSqlParser in your Java code. For example:

import ;
import ;

public class JSqlParserExample {
    public static void main(String[] args) throws Exception {
        String sql = "SELECT * FROM users WHERE id = 1";
        Statement statement = (sql);
        (statement);
    }
}

The above code is explained as follows:

  • First, we importedCCJSqlParserUtilandStatementclasses, they are part of JSqlParser.
  • existmainIn the method, we define a SQL statement stringsql。
  • Then, we use(sql)Method parses SQL statement into oneStatementObject.
  • Finally, we will parse theStatementThe object is printed out.

Please note that using different build tools (Maven, Gradle, etc.) can make it easier to manage project dependencies. It is recommended to use Maven or Gradle for dependency management, as they can automatically handle issues such as dependency version conflicts. Manually downloading JAR files may lead to version conflicts or management difficulties, especially when the project is large or has a large dependency. Also, when using JSqlParser, make sure your Java runtime version meets its requirements to avoid compatibility issues.

2. Use scenarios

  • SQL statement analysis：
  • You can use JSqlParser to parse SQL statements to extract the key information therein. For example, if you want to know oneSELECTWhich columns are selected by the statement, which table is queryed, which conditions are used, etc. can be parsed through JSqlParser. Here is a simple example:
import ;
import ;
import ;
import ;
import ;
import ;


public class JSqlParserExample {
    public static void main(String[] args) {
        String sql = "SELECT column1, column2 FROM table1 WHERE column1 = 'value'";
        try {
            Statement statement = (sql);
            if (statement instanceof Select) {
                Select selectStatement = (Select) statement;
                SelectBody selectBody = ();
                if (selectBody instanceof ) {
                     plainSelect = () selectBody;
                    List<SelectItem> selectItems = ();
                    for (SelectItem item : selectItems) {
                        ("Selected column: " + item);
                    }
                    ("Table: " + ());
                    ("Where clause: " + ());
                }
            }
        } catch (JSQLParserException e) {
            ();
        }
    }
}

Code explanation:

  • First, we use(sql)Parses SQL statements into oneStatementObject.
  • Then, we willStatementObject conversion toSelectType, because we know this is aSELECTStatement.
  • Then we passgetSelectBody()GetSelectBodyand convert it toPlainSelectType, because most simpleSELECTThe statement isPlainSelecttype.
  • Finally, we can usegetSelectItems()Get the selected column,getTable()Get the table name,getWhere()GetWHEREclause.
  • SQL statement conversion：
  • You can modify certain parts of SQL statements. For example, you might want to put oneSELECTReplace some columns in the statement with other columns, or modifyWHEREcondition. Here is an example:
import ;
import ;
import ;
import ;
import ;
import ;


public class JSqlParserModifyExample {
    public static void main(String[] args) {
        String sql = "SELECT column1, column2 FROM table1 WHERE column1 = 'value'";
        try {
            Statement statement = (sql);
            if (statement instanceof Select) {
                Select selectStatement = (Select) statement;
                SelectBody selectBody = ();
                if (selectBody instanceof ) {
                     plainSelect = () selectBody;
                    // Modify the column name                    ().clear();
                    (("column3, column4"));
                    // Modify WHERE conditions                    (("column3 &gt; 10"));
                }
                ("Modified SQL: " + statement);
            }
        } catch (JSQLParserException e) {
            ();
        }
    }
}

Code explanation:

  • First, we follow the above parse steps to parse the SQL statement toPlainSelecttype.
  • Then, we usegetSelectItems().clear()Clear the original selection and useaddSelectItems()Add new selection.
  • Finally, we usesetWhere()ReviseWHEREcondition.
  • SQL statement generation：
  • You can use JSqlParser to build new SQL statements. For example, you can use its API to create aSELECTstatements, rather than writing SQL strings manually. Here is a simple example:
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;


public class JSqlParserCreateExample {
    public static void main(String[] args) {
        // Create table object        Table table = new Table("table1");
        // Create column object        Column column1 = new Column("column1");
        Column column2 = new Column("column2");


        // Create expression column1 = 'value'        Expression equalsTo = new EqualsTo(column1, ("'value'"));
        // Create expression column2 > 10        Expression greaterThan = new GreaterThan(column2, ("10"));


        // Create AND expression column1 = 'value' AND column2 > 10        Expression where = new AndExpression(equalsTo, greaterThan);


        // Create SELECT statement        SelectExpressionItem selectItem1 = new SelectExpressionItem(column1);
        SelectExpressionItem selectItem2 = new SelectExpressionItem(column2);


        PlainSelect plainSelect = new PlainSelect();
        ((selectItem1, selectItem2));
        (table);
        (where);


        Select select = new Select();
        (plainSelect);


        ("Generated SQL: " + select);
    }
}

Code explanation:

  • First, we create table objects and column objects.

  • Then we create various expressions likeEqualsToIt means equal to the condition,GreaterThanIndicates greater than the condition and useAndExpressionCombine them intoWHEREcondition.

  • Next, we createSelectExpressionItemAs an option.

  • Finally, we combine these elements intoPlainSelectObject, then use it asSelectStatementSelectBody。

  • SQL statement verification：
  • You can use JSqlParser to verify the syntax and structure of SQL statements. For example, in a SQL editing tool, you can use JSqlParser to check whether the SQL entered by the user is legal. Here is a simple example:
import ;
import ;


public class JSqlParserValidationExample {
    public static void main(String[] args) {
        String sql = "SELECT column1, column2 FROM table1 WHERE column1 = 'value'";
        try {
            (sql);
            ("SQL is valid");
        } catch (JSQLParserException e) {
            ("SQL is invalid: " + ());
        }
    }
}

Code explanation:

  • We use(sql)Try to parse the SQL statement. If the parsing is successful, it means that the SQL statement is legal, otherwise it will be thrown.JSQLParserException, indicating that there is a problem with the SQL statement.

To summarize, JSqlParser has a wide range of applications in many aspects such as parsing, modifying, generating and verifying SQL statements, especially suitable for scenarios where dynamic operations and processing of SQL statements are required, such as SQL query optimization tools, SQL audit tools, database migration tools, etc. It provides a powerful programming method that allows you to handle SQL statements more flexibly, avoiding the errors and complexity that can be caused by manual processing of SQL strings.

3. How to deal with SQL injection attacks when using JSqlParser?

Here are some ways to handle SQL injection attacks when using JSqlParser:

1. Use prepared statements

In Java, using precompiled statements of JDBC is an important means to prevent SQL injection, and JSqlParser can be used in combination with precompiled statements. Here is a simple example:

import ;
import ;
import ;
import ;
import ;


public class JSqlParserWithPreparedStatement {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/your_database";
        String user = "username";
        String password = "password";


        try (Connection connection = (url, user, password)) {
            // Suppose the parsed SQL statement is a SELECT statement            String parsedSql = "SELECT * FROM users WHERE username =?";


            try (PreparedStatement preparedStatement = (parsedSql)) {
                // Set parameters, here assuming that user input comes from the user interface or other sources                String userInput = "admin"; 
                (1, userInput);


                try (ResultSet resultSet = ()) {
                    while (()) {
                        // Process the result set                        (("username"));
                    }
                }
            }
        } catch (SQLException e) {
            ();
        }
    }
}

explain:

  • First, we use()Establish a database connection.
  • Then, we define a placeholder containing?SQL statements, here?is a placeholder for precompiled statements.
  • use()Create a precompiled statement object.
  • pass()Set parameters such as the method, the parameters here will be escaped correctly, avoiding the risk of SQL injection.

2. Use JSqlParser to verify and normalize SQL statements

JSqlParser can be used to check whether SQL statements meet expectations, for example, to check whether SQL statements contain only allowed keywords and structures. Here is a simple example:

import ;
import ;
import ;


public class JSqlParserValidation {
    public static void main(String[] args) {
        String sql = "SELECT * FROM users WHERE username = 'admin' AND 1=1; DROP TABLE users;";


        try {
            Statement statement = (sql);
            // More verification logic can be added here            // For example, check whether there are unauthorized keywords, such as DROP, TRUNCATE, etc.            ("Parsed SQL: " + statement);
        } catch (JSQLParserException e) {
            ();
        }
    }
}

explain:

  • We use()Parses SQL statements.
  • After parsing, you can add additional verification logic, such as checking if SQL statements are includedDROP、TRUNCATEand other dangerous keywords to prevent malicious users from deleting or modifying the database structure.

3. Whitelist mechanism

Use whitelists to limit table names, column names, and operations in SQL statements. Here is a simple example:

import ;
import ;
import ;
import ;


public class JSqlParserWhiteList {
    public static final String[] ALLOWED_TABLES = {"users", "products"};


    public static void main(String[] args) {
        String sql = "SELECT * FROM users WHERE username = 'admin'";


        try {
            Statement statement = (sql);


            if (statement instanceof Select) {
                Select select = (Select) statement;
                // Suppose we only allow querying users or products tables                String tableName = ().toString().split("FROM")[1].trim().split(" ")[0];
                if (!isAllowedTable(tableName)) {
                    throw new RuntimeException("Table not allowed");
                }
                ("Parsed SQL: " + statement);
            }
        } catch (JSQLParserException e) {
            ();
        }
    }


    private static boolean isAllowedTable(String tableName) {
        for (String allowedTable : ALLOWED_TABLES) {
            if ((tableName)) {
                return true;
            }
        }
        return false;
    }
}

explain:

  • We define an array of allowed table namesALLOWED_TABLES。
  • After parsing the SQL statement,SELECTStatement, we extract the table name and check if it is in the whitelist.

4. Use parameterized query objects

JSqlParser can help you convert SQL statements into parameterized query objects, which can then be used in conjunction with precompiled statements. Here is a simple example:

import ;
import ;
import ;
import ;
import ;


public class JSqlParserParameterized {
    public static void main(String[] args) {
        String sql = "SELECT * FROM users WHERE username = 'admin' AND age &gt; 20";


        try {
            Statement statement = (sql);


            if (statement instanceof Select) {
                Select select = (Select) statement;
                // Suppose here you can extract expressions, such as username = 'admin' and age > 20                Expression whereExpression = ((Select) statement).getSelectBody().toString().split("WHERE")[1].trim();
                // Here you can further process the expression and convert it into a parameterized query object                ("Parsed Expression: " + whereExpression);
            }
        } catch (JSQLParserException e) {
            ();
        }
    }
}

explain:

  • We use()Parses SQL statements.
  • forSELECTstatements, we can extractWHEREThe expression of the clause, used as a parameterized query object, and then used in conjunction with precompiled statements, further avoiding the risk of SQL injection.

SQL injection attacks can be effectively prevented by combining JSqlParser and precompiled statements, using the whitelisting mechanism and validating SQL statements. Depending on the specific application scenario, you can flexibly select and combine these methods to ensure the security of your application.

4. Use JSqlParser to parse complex SQL statements?

The following are the steps and example codes for parsing complex SQL statements using JSqlParser in Java code:

Solution:

  • Import the related classes of JSqlParser.
  • Creates a string for SQL statements.
  • use()Method parses SQL statements intoStatementObject.
  • Depending on the type of SQL statement (for exampleSelect、Insert、Update、Delete),WillStatementThe object is type-converted.
  • Perform further operations on the converted object to extract the required information.

Sample code:

import ;
import ;
import ;
import ;
import ;
import ;

import ;


public class JSqlParserComplexExample {
    public static void main(String[] args) {
        String complexSql = "SELECT column1, column2, SUM(column3) AS total FROM table1 WHERE column1 &gt; 10 GROUP BY column1, column2 HAVING SUM(column3) &gt; 100 ORDER BY column1 ASC, column2 DESC";

        try {
            // parse SQL statements into Statement objects            Statement statement = (complexSql);

            // Determine whether the Statement object is a Select statement            if (statement instanceof Select) {
                Select selectStatement = (Select) statement;
                SelectBody selectBody = ();

                // Extract SelectItems in the Select statement                if (selectBody instanceof ) {
                     plainSelect = () selectBody;
                    List&lt;SelectItem&gt; selectItems = ();
                    for (SelectItem item : selectItems) {
                        ("Select Item: " + item);
                    }

                    // Extract Where conditions                    if (()!= null) {
                        ("Where Clause: " + ());
                    }

                    // Extract Group By clause                    if (()!= null) {
                        ("Group By Clause: " + ());
                    }

                    // Extract the Having clause                    if (()!= null) {
                        ("Having Clause: " + ());
                    }

                    // Extract Order By clause                    if (()!= null) {
                        ("Order By Clause: " + ());
                    }
                }
            }
        } catch (JSQLParserException e) {
            ();
        }
    }
}

Code explanation:

  • First, we imported the required classes of JSqlParser, including exception handling classesJSQLParserException, parsing tool classCCJSqlParserUtil, and various classes used to represent SQL statements, such asStatement、Select、SelectBodyandSelectItemwait.
  • existmainIn the method, we define a complex SQL statement stringcomplexSql。
  • Then, we use(complexSql)Method parses this complex SQL statement into aStatementObject.
  • Next, we check thisStatementIs the object aSelectstatement (because our example is aSELECTstatement), if so, we convert it toSelecttype.
  • forSelectWe further extract the statementSelectBodyand determine if it isPlainSelectType, because most simpleSELECTThe statement will be usedPlainSelectstructure.
  • We can usegetSelectItems()Method GettingSELECTAll selections in the clause and iterate over and print them.
  • forWHEREclauses, we can usegetWhere()Method gets conditional expression, if present.
  • forGROUP BYclauses, we can usegetGroupBy()Methods obtain grouping information, if present.
  • forHAVINGclauses, we can usegetHaving()Method gets filter conditions, if present.
  • forORDER BYclauses, we can usegetOrderByElements()Method gets sorting information, if present.

If the SQL statement you want to parse isINSERT、UPDATEorDELETEType, you can similarlyStatementThe object is converted to the corresponding type, and then the required information is extracted using the corresponding type method. For example:

import ;
import ;
import ;
import ;
import ;
import ;


public class JSqlParserOtherExamples {
    public static void main(String[] args) {
        String insertSql = "INSERT INTO table1 (column1, column2) VALUES (1, 'value')";
        String updateSql = "UPDATE table1 SET column1 = 2 WHERE column2 = 'value'";
        String deleteSql = "DELETE FROM table1 WHERE column1 = 3";


        try {
            // parse INSERT statement            Statement insertStatement = (insertSql);
            if (insertStatement instanceof Insert) {
                Insert insert = (Insert) insertStatement;
                ("Insert Table: " + ());
                ("Insert Columns: " + ());
                ("Insert Values: " + ());
            }


            // parse UPDATE statement            Statement updateStatement = (updateSql);
            if (updateStatement instanceof Update) {
                Update update = (Update) updateStatement;
                ("Update Table: " + ());
                ("Update Set Items: " + ());
                ("Update Where Clause: " + ());
            }


            // parse DELETE statement            Statement deleteStatement = (deleteSql);
            if (deleteStatement instanceof Delete) {
                Delete delete = (Delete) deleteStatement;
                ("Delete Table: " + ());
                ("Delete Where Clause: " + ());
            }
        } catch (JSQLParserException e) {
            ();
        }
    }
}

Code explanation:

  • forINSERTStatement, we willStatementConvert toInsertType, then can be usedgetTable()Method to get the inserted table name,getColumns()Method to get the inserted column name list,getItemsList()Method gets the inserted value list.
  • forUPDATEStatement, we willStatementConvert toUpdateType, then can be usedgetTable()Method to get the updated table name,getSets()Method gets the updated column and value mapping,getWhere()Method to get the updated conditions.
  • forDELETEStatement, we willStatementConvert toDeleteType, then can be usedgetTable()Method to get the deleted table name,getWhere()Method to get the conditions for deletion.

Through the above method, you can flexibly use JSqlParser to parse different types of complex SQL statements and extract various information to meet your specific needs. Follow Wei Ge Ai Programming, full-stack development will definitely be successful.

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